A universal ratiometric photoelectrochemical (PEC) bioassay, which could be readily expanded for ultrasensitive determination of various targets in complex biological matrixes, was established by coupling a target-nucleotide transduction-amplification with DNA nanomachine mediated electron-transfer tunneling distance regulation strategies. With the help of target-nucleotide transduction-amplification strategy, the one input target signal could be transducted to corresponding multiple output DNA signals by nucleotide specific recognition technology, simultaneously leading to an efficient signal amplification for target. Then the output DNA could initiate the formation of four-way junction DNA nanomachine through binding-induced combination, by which the electron-transfer tunneling distance between photoactive materials and sensing interface could be regulated, simultaneously resulting an enhanced photocurrent signal from SiO2@methylene blue (SiO2@MB) as wavelength-selective photoactive material in close proximity to sensing interface and a reduced photocurrent signal from another wavelength-selective photoactive material CdS quantum dots (CdS QDs) away from sensing interface for photocurrent signal ratio calculation. Using microRNA-141 (miRNA-141) as target model, the constructed biosensor demonstrated favorable accuracy and excellent sensitivity down to the femtomolar level. Impressively, the proposed assay overcame the heavy dependence of target on photoactive materials in current ratiometric PEC assay and demonstrated admirably universal applicability for determination of various targets such as metal ions, miRNAs, DNAs, and proteins by merely two different photoactive materials (SiO2@MB and CdS QDs), paving the way to application of universal ratiometric PEC assay in environmental tests, clinical diagnosis, and other related subjects.

In this work, an improved target-triggering nicking enzyme signaling amplification (NESA) strategy as signal enhancer has been fabricated to obtain a sensitive electrochemical thrombin (TB) biosensor combined with PtPd NPs decorated electroactive Co-based metal–organic frameworks (Co-MOFs/PtPdNPs) as a redox mediator. Traditionally, in the NESA strategy, only one of the output double strands DNA is available in the next cycle. However, in this work, all of the output DNA involved in the improved NESA strategies could be further employed, resulting in high utilization of output DNA, which further enhanced signal amplification and sensitivity of the biosensor. In addition, the electroactive Co-MOFs were not only used as nanocarriers but also acted as signal labels, avoiding adding extra redox media. Simultaneously, in the presence of H2O2, PtPd NPs decorated on the Co-MOFs act the same as horseradish peroxidase to promote the oxidation of H2O2, further promoting the conversion of Co2+ to Co3+, leading to electrochemical signal amplification. With such design, the TB biosensor exhibited good sensitivity from 1 pM to 30 nM with a detection limit of 0.32 pM. This new NESA strategy with high utilization of output DNA can supply one efficient approach to improve signal amplification, which also open an avenue for sensitivity enhancement in detection of analytes.

Herein, an ultrasensitive electrochemiluminescent (ECL) strategy was designed based on the fabrication of a multi-interface DNA micronet-carrier via layer by layer hybridization of double-stranded DNAzyme-substrate to immobilize large amounts of ECL indicator, [Ru(dcbpy)2dppz]2+, in double-strand DNA on the electrode surface, generating enhanced ECL signals. When the double-stranded structures were cleaved circularly via Pb2+ in the detection sample, the ECL indicator was released, which resulted in a decreased ECL signal associated with the concentration of Pb2+, that had higher sensitivity and wider linear range. As a result, the developed ECL strategy exhibited a linear range from 50 pM to 500 μM with a detection limit of 4.73 pM, providing an alternative analytical strategy with excellent properties, including a high sensitivity and a wide linear range. Importantly, the ECL strategy could be readily expanded for various metal ions, proteins, nucleotide sequences, and cells, offering a simple and efficient technology for both environmentally safe assays and clinical diagnostics.Keywords: circular etching; DNA micronet; DNAzyme; electrochemiluminescent assay; metal ion; nucleotide sequences;

Electrochemiluminescence (ECL) with high sensitivity and excellent controllability provides a promising approach for ultrasensitive detection of multiple biomarkers. However, the detection for multiple types of biomarkers on a single interface remains a considerable challenge owing to the functional differentiation of different types of biomarkers. Herein, we utilized “on–off–on” switching, target-induced cleavage of peptide, and TdT (terminal deoxynucleoside transferase)-mediated extension successfully constructing a novel ECL biosensor for the ultrasensitive detection of microRNA-141 (miRNA-141) and matrix metalloproteinase-2 (MMP-2). Importantly, the dual biomarkers are related with several identical cancers, which endow the biosensor with diagnostic accuracy and efficiency. In this protocol, target 1 (miRNA-141) first hybridized with probe DNA (pDNA) assembled on CdS QDs modified sensing surface. Afterward, miRNA-141 captured trigger DNA (tDNA) to generate a long ssDNA nanotail via TdT-mediated DNA polymerization. Then the forming ssDNA could capture abundant Fc-peptide-ssDNA conjugates through the hybridization reaction, the ECL intensity quenched significantly due to the efficient quenching effect of Fc to CdS QDs, realizing the ultrasensitive detection of miRNA-141 with a detection limit of 33 aM (S/N = 3). After incubated with target 2 (MMP-2) which specifically cleaved the Fc-peptide-ssDNA conjugates causing the releasing of Fc from the sensing surface, the ECL intensity had an obvious enhancement, achieving the ultrasensitive analysis of MMP-2 with a detection limit of 33 fg·mL–1 (S/N = 3). More importantly, this biosensor also realized the monitoring of biomarkers in different cancer cells and human serum, which indicated that the biosensing system could serve as applicable tools in clinical analysis.

Nanomaterials themselves as redox probes and nanocatalysts have many advantages for electrochemical biosensors. However, most nanomaterials with excellent catalytic activity cannot be directly used as redox probe to construct electrochemical biosensor because the redox signal of these nanomaterials can only be obtained in strong acid or alkali solution at high positive or negative potential, which greatly limits their applications in biologic assay. In this study, Cu/Mn double-doped CeO2 nanocomposite (CuMn-CeO2) was synthesized to use as signal tags and signal amplifiers for the construction of electrochemical immunosensor for sensitive assay of procalcitonin (PCT). Herein, CuMn-CeO2 not only possesses excellent catalytic activity toward H2O2 for signal amplification, but also can be directly used as redox probe for electrochemical signal readout achieved in neutral mild buffer solution at low positive potential. Importantly, since doping Cu, Mn into CeO2 lattice structure can generate extra oxygen vacancies, the redox and catalytic performance of obtained CuMn-CeO2 was much better than that of pure CeO2, which improves the performance of proposed immunosensor. Furthermore, CuMn-CeO2 can be implemented as a matrix for immobilizing amounts of secondary antibody anti-PCT by forming ester-like bridging between carboxylic groups of Ab2 and CeO2 without extra chemical modifications, which greatly simplifies the preparative steps. The prepared immunosensor exhibited a wide linear range of 0.1 pg mL–1 to 36.0 ng mL–1 with a low detection limit of 0.03 pg mL–1. This study implements nanomaterial themselves as redox probes and signal amplifiers and paves a new way for constructing electrochemical immunosensor.

Herein, we fabricated a novel electrochemiluminescence (ECL) biosensor for ultrasensitive detection of mucin 1 (MUC1) based on a three-dimensional (3-D) DNA nanomachine signal probe powered by protein-aptamer binding complex. The assembly of 3-D DNA nanomachine signal probe achieved the cyclic reuse of target protein based on the protein-aptamer binding complex induced catalyzed hairpin assembly (CHA), which overcame the shortcoming of protein conversion with enzyme cleavage or polymerization in the traditional examination of protein. In addition, CoFe2O4, a mimic peroxidase, was used as the nanocarrier of the 3-D DNA nanomachine signal probe to catalyze the decomposition of coreactant H2O2 to generate numerous reactive hydroxyl radical OH• as the efficient accelerator of N-(aminobutyl)-N-(ethylisoluminol) (ABEI) ECL reaction to amplify the luminescence signal. Simultaneously, the assembly of 3-D DNA nanomachine signal probe was executed in solution, which led to abundant luminophore ABEI be immobilized around the CoFe2O4 surface with amplified ECL signal output since the CHA reaction was occurred unencumberedly in all directions under homogeneous environment. The prepared ECL biosensor showed a favorable linear response for MUC1 detection with a relatively low detection limit of 0.62 fg mL–1. With excellent sensitivity, the strategy may provide an efficient method for clinical application, especially in trace protein determination.

An ultrasensitive fluorescence assay for intracellular Pb2+ determination was proposed through target–intermediate recycling amplification based on metal-assisted DNAzyme catalysis and strand displacement reactions. Compared with only target recycling-based fluorescence assay with an M amplification ratio, the proposed assay could achieve an M × N amplification ratio to obtain an improved sensitivity by more than 10 times, in which M and N are the amplification ratios of target recycling and intermediate recycling, respectively. Remarkably, this proposed ultrasensitive fluorescence assay could be applied to the determination of various analytes with the well-designed detection probe, especially in intracellular assay, providing a promising tool for clinical diagnosis and biomedical detection.

Herein, a novel electrochemical impedimetric biosensor for the heparanase (HPA) assay was developed based on target protein-induced DNA hydrogel formation, followed by pH-stimulation of the hydrogel density to increase the signal amplification. The method involved the synthesis of two different copolymer chains, consisting of two cooperatively functioning cross-linking elements, where one element was associated with the HPA-response and the other one with the pH-response. Initially, single-strand DNA as a capture probe was modified on the electrode surface. In the presence of HPA, the HPA-responsive element binding to HPA-induced DNA hybridization between the two copolymer chains and captured DNA, giving rise to the formation of a low-density polymer hydrogel film on the electrode surface and it obtaining an obvious impedimetric response. A significant signal enhancement was observed when changing the pH of the hydrogel film to 5.0, which could be ascribed to the fact that the pH-responsive element can fold into four-stranded i-motif structures at pH 5.0, leading to the increase in density of the hydrogel film. By implementing the DNA hydrogel to induce an impedimetric response change, this impedimetric biosensor exhibited an excellent analytical performance towards the HPA quantitative assay, with a low detection limit of 0.003 pg mL−1. This new method provides a versatile signal amplification method and paves a new way to construct impedimetric sensors for bioassays.

•PtNPs@Co(II)MOFs@PtNPs could act as electroactive materials, redox probe and signal enhancer.•PtNPs modified on the suface of MOFs and encapsulated in the MOFs exhibit high catalytic activity.•PtNPs@Co(II)MOFs@PtNPs with large surface area were used as nanocarriers.In this work, a Pt nanoparticles-functionalized Co-based metal organic frameworks (PtNPs@Co(II)MOFs@PtNPs) was synthesized and applied in electrochemical aptasensor for thrombin (TB) detection. First, the Co(II)MOFs@PtNPs were prepared via the mixed solvothermal method, which consists of inner Pt nanoparticles (PtNPs) encapsulated by aminofunctionalized Co(II)MOFs materials. Following that, additional PtNPs were adsorbed on the surface of Co(II)MOFs@PtNPs, resulting in the formation of PtNPs@Co(II)MOFs@PtNPs nanocomposite. The PtNPs@Co(II)MOFs@PtNPs nanocomposites with a large surface area were implimented as nanocarriers to immobilize a mass of TBA II for the formation of the TBA II bioconjugates that could be captured onto the electrode surface by sandwich-type format. Moreover, the PtNPs@Co(II)MOFs@PtNPs nanocomposites could directly use as redox tags for charge-generating and electron-transporting with the electron transfer from Co(II) to Co(III). Furthermore, in the presence of H2O2, the PtNPs@Co(II)MOF@PtNPs could effectively catalyze H2O2 oxidation with improvement electron transfer of redox probe, resulting in electrochemical signal amplification. Based on the above superior advantages, TB was determined in the concentration range from 0.1 pM to 50 nM with a detection limit of 0.33 fM. Furthermore, the excellent sensitivity and selectivity can be easily established for quantitative analysis of other analytes.A novel electrochemical aptasensor has been developed using Pt nanoparticles-functionalized Co-based metal organic frameworks (PtNPs@Co-MOFs@PtNPs) as redox probe and signal enhancer for sensitive thrombin (TB) detection.Download high-res image (186KB)Download full-size image

The construction of DNA nanomachines holds great significance in the development of DNA nanostructures; however, the real application of nanomachines is still in its early stage. Moreover, one-step regenerated sensing platforms for the detection of biomarkers in the current research remain a practical challenge. Herein, a novel electrochemiluminescence resonance energy transfer (ERET) strategy between Alexa Flour 488 (AF 488), which is a type of small molecule dye, as the donor and CdSe@ZnS quantum dots (QDs) as the acceptor, which easily enter the cells, has been reported and was applied for the construction of a DNA nanomachine-based regenerated biosensor for the ultra-high sensitive determination of cancer cells without any enzyme. First, a dual amplification strategy, including target recycling and signal transformation, was employed to achieve the conversion of a small number of miRNAs into a large amount of universal DNA reporters. Initially, the DNA tweezer was kept in the “off” state with two arms labeled with QDs and AF488, respectively. Second, in the presence of DNA reporters, the tweezer transformed to the “on” state through the hybridization of the reporter DNA and exposed the arms of the tweezer. Simultaneously, QDs and AF488 on the two arms were close enough to generate ERET, which remarkably increased the ECL intensity of the QDs. Impressively, the sensor could be regenerated by a one-step strand displacement and could be cycled for more than seven times. Owing to the dual amplification strategy and the high efficiency of the ERET between the QDs and AF488, the proposed biosensor performs in the linear range from 10 pM to 0.1 fM with a detection limit of 0.03 fM for miRNA determination, and the monitoring of different cancer cells was also achieved. Moreover, the elaborated biosensor can also realize the sensitive detection of Pb2+, which indicates that it can be potentially used for field environmental analysis and monitoring, thus offering a new modular platform for the construction of functional DNA nanomachines in the ultra-high sensitive analysis of promising biomarkers and toxic metals.

Herein, a high-efficiency electrochemiluminescence (ECL) indicator of an abundant N-(aminobutyl)-N-(ethylisoluminol) functionalized metal–organic framework (ABEI@Fe-MIL-101) was synthesized to construct a biosensor for the ultrasensitive assay of mucin1 on MCF-7 cancer cells with a coreactant H2O2-free strategy.

Based on the novel designed K-junction structure, an economic and efficient exponential signal amplification strategy with simple protocol combining hemin/G-quadruplex, a mimetic peroxidase, as a catalyzer was proposed and utilized in an electrochemiluminescence biosensor for sensitive microRNA detection. It was noteworthy that the K-junction structure was formed with guanine-rich reporter DNA and substrate DNA modified by phosphate at the 5′-terminus. Thus, the activity of the reporter DNA could be inhibited and the recognition domain for the target microRNA constructed through the K-junction structure formed. When the target microRNA was sensed, the paired domains of the substrate DNA was completely digested from the 5′-terminus, accompanied by the release of the target microRNA and unpaired DNA fragment of the substrate DNA called the trigger DNA. Afterwards, the released microRNA and trigger DNA were recycled over and over causing the linear and exponential digestion of the K-junction structure, respectively. As a result, numerous uninhibited reporter DNAs were left on the electrode to capture hemin with the yielded hemin/G-quadruplex, which could enhance the ECL emission significantly due to its catalysis for the luminol–H2O2. As expected, this method exhibited excellent specificity and high sensitivity for microRNA detection from 0.033 fM. What's more, the application in human lung cancer cell lines achieved good sensitivity for 10 tumor cells.

In this work, an “off” to “on” surface-enhanced Raman spectroscopy (SERS) platform was constructed for ultrasensitive detection of microRNA (miRNA) by using a magnetic SERS substrate (Co@C/PEI/Ag) and padlock probe-based exponential rolling circle amplification (P-ERCA) strategy. Herein, miRNA 155 could act as primers to initiate rolling circle amplification (RCA) for producing a long repeat sequence, and then the obtained DNA would be cleaved into two kinds of single-stranded DNAs in the presence of nickase. One of the DNAs can be a new primer to initiate new cycle reactions for obtaining large numbers of the other one (trigger DNA), consequently leading to an exponential amplification. On the other hand, the hairpin DNA (H1), with a Raman label (Cy5) at one end, would form a hairpin structure to make the Cy5 closer to the SERS substrates, which could produce a strong SERS signal (“on” status). Then placeholder DNA (P2) partly hybridized with H1 to open the hairpin structure making Cy5 far away from substrates with a decreased signal (“off” status). Next, the obtained trigger DNA can complement with P2 to make the Raman label reclosed to the SERS substrates with a strong SERS signal (“on” status). From this principle, the strategy could achieve the change from “off” to “on” status. This SERS strategy exhibited a wide linear range of 100 aM to 100 pM with a low detection limit of 70.2 aM, which indicated the proposed SERS platform has potential application value for ultrasensitive bioassay of miRNA.

The determination of multiple biomarkers from cancer cells features a considerable step toward early diagnosis of cancers. However, realizing different biomarkers detection with single electrochemiluminescence (ECL) luminophore and regenerating the sensing platform remain a compelling goal. Herein, dual miRNAs-fueled DNA nanogears were designed for an enzyme-free ECL biosensor construction to perform the multiple sensitive detection of the microRNA (miRNA) biomarkers with single luminophore. The nanogears were assembled on CdS quantum dots (QDs) modified sensing surface. Using miRNA-21 as motive power, Au nanoparticles (AuNPs)-labeled nanogears B could be activated to roll against nanogear A, increasing the distance between AuNPs and CdS QDs. Thus, the significant ECL enhancement of CdS QDs was obtained owing to the ECL energy transfer between AuNPs and CdS QDs, simultaneously realizing the detection of miRNA-21. After the incubation of miRNA-155, nanogear B revolved against nanogear A continuously and realized the close-range of AuNPs and CdS QDs, resulting in the quenching of ECL intensity due to the Förster energy transfer and realizing the analysis of miRNA-155. The successive locomotion of the nanogears led to a significant ECL increasing for analysis of miRNA-21 down to 0.16 fM and a remarkable ECL suppression for determination of miRNA-155 down to 0.33 fM. Impressively, the proposed biosensor was able to be regenerated along with the gears roll against each other. In general, this enzyme-free strategy initiates a new thought to realize the multiple ECL detection with single luminophore, paving the way for applications of nanomachines in biosensing and clinical diagnosis.

Here, an ultrasensitive “off–on” electrochemiluminescence (ECL) biosensor was proposed for the determination of telomerase activity by using a self-enhanced ruthenium polyethylenimine (Ru–PEI) complex doped zeolitic imidazolate framework-8 (Ru–PEI@ZIF-8) with high ECL efficiency as an ECL indicator and an enzyme-assisted DNA cycle amplification strategy. The Ru–PEI@ZIF-8 nanocomposites were synthesized by self-enhanced Ru–PEI complex doping during the growth of zeolitic imidazolate framework-8 (ZIF-8), which presented high ECL efficiency and excellent stability. Furthermore, owing to the porosity of Ru–PEI@ZIF-8, the self-enhanced Ru–PEI complex in the outer layer and inner layer of self-enhanced Ru–PEI@ZIF-8 could be excited by electrons causing the utilization ratio of the self-enhanced ECL materials to be remarkably increased. To further improve the sensitivity of the proposed biosensor, the telomerase activity signal was converted into the trigger DNA signal which was further amplified by an enzyme-assisted DNA recycle–amplification strategy. The proposed ECL biosensor presented great performance for telomerase activity detection from 5 × 101 to 106 Hela cells with a detection limit of 11 cells. Moreover, this method was applied in the detection of telomerase activity from cancer cells treated with an anticancer drug, which indicated the proposed method held potential application value as an evaluation tool in anticancer drug screening.

•The Ir(ppy)3 doped silica nanoparticles (SiO2@Ir) performed improved ECL emissions.•The ECL emission of SiO2@Ir could be quenched via H2O2 from enzymatic reaction.•A ECL sandwich immunosensor was proposed with improved performances.•The ECL strategy revealed a new avenue for early diagnosis of various diseases.A sensitive electrochemiluminescent (ECL) sandwich immunosensor was proposed herein based on the tris (2-phenylpyridine) iridium [Ir(ppy)3] doped silica nanoparticles (SiO2@Ir) with improved ECL emission as signal probes and glucose oxidase (GOD)-based in situ enzymatic reaction to generate H2O2 for efficiently quenching the ECL emission of SiO2@Ir. Typically, the SiO2@Ir not only increased the loading amount of Ir(ppy)3 as ECL indicators with high ECL emission, but also improved their water-solubility, which efficiently enhanced the ECL emission. Furthermore, by the efficient quench effect of H2O2 from in situ glucose oxidase (GOD)-based enzymatic reaction on the ECL emission of SiO2@Ir, a signal-off ECL immunsensor could be established for sensitive assay. With N-terminal of the prohormone brain natriuretic peptide (BNPT) as a model, the proposed ECL assay performed high sensitivity and low detection limit. Importantly, the proposed sensitive ECL strategy was not only suitable for the detection of BNPT for acute myocardial infarction, but also revealed a new avenue for early diagnosis of various diseases via proteins, nucleotide sequence, microRNA and cells.

Herein, a self-enhanced N-(aminobutyl)-N-(ethylisoluminol) (ABEI) derivative-based electrochemiluminescence (ECL) immunosensor was constructed for the determination of laminin (LN) using PdIr cubes as a mimic peroxidase for signal amplification. Initially, PdIr cubes with efficient peroxidase mimicking properties, large specific surface areas, and good stability and uniformity were synthesized. Then, L-cysteine (L-Cys) and ABEI were immobilized on the PdIr cubes to form the self-enhanced ECL nanocomplex (PdIr-L-Cys-ABEI). In this nanocomplex, PdIr cubes, whose catalytic constant is higher than that of horseradish peroxidase (HRP), could effectively catalyze H2O2 decomposition and thus enhance the ECL intensity of ABEI. Moreover, PdIr cubes can be easily modified with functional groups, which make them adaptable to desired supported platforms. On the other hand, L-Cys as a coreactant of ABEI could effectively enhance the luminous efficiency due to the intramolecular ECL reaction which could reduce the energy loss between L-Cys and ABEI by giving a shorter electron transfer distance. The developed strategy combined an ABEI derivative as a self-enhanced ECL luminophore and PdIr cubes as a mimic peroxidase, resulting in a significantly enhanced ECL signal output. Also, the strategy showed high sensitivity and selectivity for LN, which suggested that our new approach could be potentially applied in monitoring different proteins.

In this work, a series of novel multifunctionalized peryleneteracarboxylic supramolecules were synthesized based on hydrogen bonding interactions between 3,4,9,10-perylenetetracarboxylic acid (PTCA) and amines, which possess large specific surface area, good membrane-forming properties and high stability. Importantly, an interesting phenomenon was found in that these series of supramolecules could conciliate disorderly redox peaks of PTCA and result in a pair of well-defined redox peaks, which were able to act as redox carriers for charge-generation and electron-transportion. And the probable mechanism for this phenomenon was discussed for the first time in detail through the integration of theoretical with practical research. To further reveal the advantages of these novel multifunctionalized supramolecule nanomaterials, PTCA/triethylamine (PTCA/TEA) was chosen as the best candidate for a redox carrier to participate in a “signal-on” aptasensor for thrombin (TB) detection by employing Fe3O4 magnetic beads (MBs) as a good enzyme mimic to catalyze the PTCA/TEA for signal amplification. As a result, a wide linear detection range of 0.0001–50 nM is acquired with a relatively low detection limit of 0.05 pM. And the proposed aptasensor exhibited good specificity and acceptable reproducibility and stability. After all, the explorations between PTCA and amines would set up a meaningful basis in seeking multifunctionalized supramolecule nanomaterials based on PTCA for extending the application of PTCA in a wider range of fields, and exploring the essential reason for the referred peculiar phenomenon for PTCA.

N-terminal pro-brain natriuretic peptide (NT-proBNP) has been demonstrated to be a sensitive and specific biomarker for heart failure (HF). Surface-enhanced Raman spectroscopy (SERS) technology can be used to accurately detect NT-proBNP at an early stage for its advantages of high sensitivity, less wastage and time consumption. In this work, we have demonstrated a new SERS-based immunosensor for ultrasensitive analysis of NT-proBNP by using metal–organic frameworks (MOFs)@Au tetrapods (AuTPs) immobilized toluidine blue as SERS tag. Here, MOFs@AuTPs complexes were utilized to immobilize antibody and Raman probe for their excellent characteristics of high porosity, large surface area, and good biocompatibility which can obviously enhance the fixing amount of biomolecule. To simplify the experimental operation and improve the uniformity of the substrate, Au nanoparticles functionalized CoFe2O4 magnetic nanospheres (CoFe2O4@AuNPs) were further prepared to assemble primary antibody. Through sandwiched antibody–antigen interactions, the immunosensor can produce a strong SERS signal to detect NT-proBNP fast and effectively. With such design, the proposed immunosensor can achieve a large dynamic range of 6 orders of magnitude from 1 fg mL–1 to 1 ng mL–1 with a detection limit of 0.75 fg mL–1. And this newly designed amplification strategy holds high probability for ultrasensitive immunoassay of NT-proBNP.Keywords: CoFe2O4 nanoparticles; immunoassay; metal−organic frameworks; N-terminal pro-brain natriuretic peptide; SERS

In this work, ceria doped ZnO nanomaterials with flower-structure (Ce:ZONFs) were prepared to construct a luminol-based electrochemiluminescence (ECL) immunosensor for amyloid-β protein (Aβ) detection. Herein, carboxyl groups (−COOH) covered Ce:ZONFs were synthesized by a green method with lysine as reductant. After that, Ce:ZONFs-based ECL nanocomposite was prepared by combining the luminophore of luminol and Ce:ZONFs via amidation and physical absorption. Luminol modified on Ce:ZONFs surface could generate a strong ECL signal under the assistance of reactive oxygen species (ROSs) (such as OH• and O2•–), which were produced by a catalytic reaction between Ce:ZONFs and H2O2. It was worth noticing that a quick Ce4+ ↔ Ce3+ reaction in this doped material could increase the rate of electron transfer to realize the signal amplification. Subsequently, the luminol functionalized Ce:ZONFs (Ce:ZONFs-Lum) were covered by secondary antibody (Ab2) and glucose oxidase (GOD), respectively, to construct a novel Ab2 bioconjugate (Ab2-GOD@Ce:ZONFs-Lum). The wire-structured silver–cysteine complex (AgCys NWs) with a large number of −COOH, which was synthesized by AgNO3 and l-cysteine, was used as substrate of the immunosensor to capture the primary antibody (Ab1). Under the optimal conditions, this proposed ECL immunosensor had exhibited high sensitivity for Aβ detection with a wide linear range from 80 fg/mL to 100 ng/mL and an ultralow detection limit of 52 fg/mL. Meanwhile, this biosensor had good specificity for Aβ, indicating that the provided strategy had a promising potential in the detection of Aβ.

In this work, an ultrasensitive “on–off–on” photoelectrochemical (PEC) aptasensor was proposed based on the signal amplification of a fullerene/CdTe quantum dot (nano-C60/CdTe QDs) sensitized structure and efficient signal quenching of nano-C60/CdTe QDs by a manganese porphyrin (MnPP).

In this work, an electrochemical peptide biosensor was developed for matrix metalloproteinase-2 (MMP-2) detection by conversion of a peptide cleavage event into DNA detection with exonuclease III (Exo III)-assisted cycling signal amplification.

Here, a novel sensitive electrochemiluminescence (ECL) biosensor using N doped carbon dots (N-CDs) in situ electro-polymerized onto a glassy carbon electrode (GCE) as luminophores, and Pd–Au hexoctahedrons (Pd@Au HOHs) as enhancers, was developed for the detection of intracellular lead ions (Pb2+).

A self-enhanced electrochemiluminescence (ECL) reagent, synthesized by covalently linking bis(2,2′-bipyridyl)(4′-methyl-[2,2′]bipyridinyl-4-carboxylicacid) ruthenium(II) (Ru(bpy)2(mcbpy)2+) with tris(3-aminopropyl)amine (TAPA), has been chosen as precursor to prepare nanorods ([Ru(bpy)2(mcbpy)2+-TAPA]NRs) with high luminous efficiency via a solvent-evaporation-induced self-assembly procedure. Due to the shorter electron-transfer path and less energy loss, the intramolecular reaction between the luminescent Ru(bpy)2(mcbpy)2+ and coreactive tertiary amine group in TAPA has shown improved luminous efficiency compared with the common intermolecular ECL reactions. Moreover, using the electrochemiluminescent Ru(II)-based complex as precursor to directly prepare a nanostructure with high electro-active surface area is a more effective and convenient method for enhancing the immobilized amount of Ru(II)-based complex in the construction of biosensors compared with the traditional immobilized methods. Meanwhile, the obtained nanorods could be further functionalized easily, owing to their positive electrical property and the amino group on the surface. Here, Pt nanoparticles functionalized [Ru(bpy)2(mcbpy)2+-TAPA]NRs are used to load the detection antibody (Ab2). In addition, the Au/Pd dendrimers (DRs) with hierarchically branched structures are synthesized to immobilize capture antibody (Ab1) with increased amount. Based on sandwiched immunoreactions, a simple and sensitive “signal-on” immunosensor is constructed for the detection of N-acetyl-β-d-glucosaminidase (NAG), a biomarker of diabetic nephropathy, with excellent linearity in concentrations from 1 ng mL–1 to 0.5 pg mL–1 and a detection limit of 0.17 pg mL–1.

Electrochemiluminescent (ECL) assay with high sensitivity has been considered as one of the potential strategies to simultaneously detect multiple biomarker proteins. However, it was essential, but full of challenges, to overcome the limitation caused by cross reactions among different ECL indicators. Herein, the multiparameter analysis of ECL-potential signals demonstrated by multivariate linear algebraic equations was first employed in the simultaneous ECL assay to realize multiple detection of biomarker proteins on a single interface. Additionally, owing to the exponential amplification of self-synthesized nucleotide dendrimer by hybridization chain reaction (HCR) and rolling circle amplification (RCA), the developed simultaneous ECL assay showed improved sensitivity and satisfactory accuracy for the detection of N-terminal of the prohormone brain natriuretic peptide (BNPT) and cardiac troponin I (cTnI). Furthermore, a self-designed magnetic beads-based flow system was also employed to improve the feasibility and analysis speed of the simultaneous ECL assay. Importantly, the proposed strategy enabled simultaneous detection of multiple biomarker proteins simply, which could be readily expanded for the multiplexed estimation of various kinds of proteins and nucleotide sequence also, revealing a new avenue for early disease diagnosis with higher efficiency.

The preparation of self-assembled DNA nanostructure with different sizes and shapes has been one of the most promising research areas in recent years, while the application of these DNA nanostructures in biosensors is far from fully developed. Here, we presented a novel carrier system to construct an electrochemiluminescence (ECL) aptasensor for ultrasensitive determination of lipopolysaccharides (LPS) on the basis of self-assembled tetrahedron DNA dendrimers. Doxorubicin (Dox), a well-known intercalator of double stranded DNA (dsDNA), was conjugated with the ECL luminophore of N-(aminobutyl)-N-(ethylisoluminol) (ABEI) to form a new type of ECL indicators (Dox-ABEI), which could noncovalently attach to dsDNA through intercalation. Based on this property, self-assembled tetrahedron DNA dendrimers were employed as an efficient nanocarrier to achieve a high loading efficiency for Dox-ABEI with significantly amplified ECL signal output. Streptavidin (SA) and biotin, a typical ligand–receptor pair, has been chosen to anchor the tetrahedron DNA dendrimers on the electrode surface. Moreover, by converting LPS content into DNA output, catalyzed hairpin assembly (CHA) target recycling signal amplification strategy was also adopted to enhance the sensitivity of the ECL aptasensor. With combining the loading power of the tetrahedron DNA dendrimers for ECL indicators, the inherent high sensitivity of ECL technique and target recycling for signal amplification, the proposed strategy showed a detection limit of 0.18 fg/mL for LPS.

Here, a novel “light-switch” molecule of Ru (II) complex ([Ru(dcbpy)2dppz]2+-DPEA) with self-enhanced electrochemiluminescence (ECL) property is proposed, which is almost nonemissive in aqueous solution but is brightly luminescent when it intercalates into DNA duplex. Owing to less energy loss and shorter electron-transfer distance, the intramolecular ECL reaction between the luminescent [Ru(dcbpy)2dppz]2+ and coreactive tertiary amine group in N,N-diisopropylethylenediamine (DPEA) makes the obtained “light-switch” molecule possess much higher light-switch efficiency compared with the traditional “light-switch” molecule. For increasing the loading amount and further enhancing the luminous efficiency of the “light-switch” molecule, biotin labeled DNA dendrimer (the fourth generation, G4) is prepared from Y-shape DNA by a step-by-step assembly strategy, which provides abundant intercalated sites for [Ru(dcbpy)2dppz]2+-DPEA. Meanwhile, the obtained nanocomposite (G4-[Ru(dcbpy)2dppz]2+-DPEA) could well bind with streptavidin labeled detection antibody (SA-Ab2) due to the existence of abundant biotin. Through sandwiched immunoreaction, an ECL immunosensor was fabricated for sensitive determination of N-acetyl-β-d-glucosaminidase (NAG), a typical biomarker for diabetic nephropathy (DN). The detemination linear range was 0.1 pg mL–1 to 1 ng mL–1, and the detection limit was 0.028 pg mL–1. The developed strategy combining the ECL self-enhanced “light-switch” molecular and DNA nanotechnology offers an effective signal amplification mean and provides ample potential for further bioanalysis and clinical study.

In this work, a self-enhanced ultrasensitive photoelectrochemical (PEC) biosensor was established based on a functionalized nanocapsule packaging both donor–acceptor-type photoactive material and its sensitizer. The functionalized nanocapsule with self-enhanced PEC responses was achieved first by packaging both the donor–acceptor-type photoactive material (poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl}, PTB7-Th) and its sensitizer (nano-C60, fullerene) in poly(ethylene glycol) (PEG) to form a nanocapsule, which significantly enhanced PEC signal and stability of the PEC biosensor. Moreover, a quadratic enzymes-assisted target recycling amplification strategy was introduced to the system for ultrasensitive determination. Compared with other established PEC biosensors, our proposed self-enhanced approach showed higher effectivity, accuracy, sensitivity, and convenience without any addition of coreactant or sensitizers into the testing electrolyte for photocurrent amplification and performed excellent analytical properties for microRNA estimation down to femtomole level with microRNA-141 as a model. Additionally, the proposed PEC biosensor was employed for estimation of microRNA in different cancer cells and pharmacodynamic evaluation in cancer cells. This self-enhanced PEC strategy has laid the foundation for fabrication of simple, effective, and ultrasensitive PEC diagnostic devices, leading to the possibility for early diagnosis, timely stage estimation, and accurate prognosis judgment of disease.

In the present work, we first found that mercury ion (Hg2+) has an efficient quenching effect on the electrochemiluminescence (ECL) of N-(aminobutyl)-N-(ethylisoluminol) (ABEI). Since we were inspired by this discovery, an aptamer-based ECL sensor was fabricated based on a Hg2+ triggered signal switch coupled with an exonuclease I (Exo I)-stimulated target recycling amplification strategy for ultrasensitive determination of Hg2+ and mucin 1 (MUC1). Concretely, the ECL intensity of ABEI-functionalized silver nanoparticles decorated graphene oxide nanocomposite (GO-AgNPs-ABEI) was initially enhanced by ferrocene labeled ssDNA (Fc-S1) (first signal switch “on” state) in the existence of H2O2. With the aid of aptamer, assistant ssDNA (S2) and full thymine (T) bases ssDNA (S3) modified Au nanoparticles (AuNPs-S2-S3) were immobilized on the sensing surface through the hybridization reaction. Then, via the strong and stable T-Hg2+-T interaction, an abundance of Hg2+ was successfully captured on the AuNPs-S2-S3 and effectively inhibited the ECL reaction of ABEI (signal switch “off” state). Finally, the signal switch “on” state was executed by utilizing MUC1 as an aptamer-specific target to bind aptamer, leading to the large decrease of the captured Hg2+. To further improve the sensitivity of the aptasensor, Exo I was implemented to digest the binded aptamer, which resulted in the release of MUC1 for achieving target recycling with strong detectable ECL signal even in a low level of MUC1. By integrating the quenching effect of Hg2+ to reduce the background signal and target recycling for signal amplification, this proposed ECL aptasensor was successfully used to detect Hg2+ and MUC1 sensitively with a wide linear response.

In this work, a highly effective protein converting strategy based on immunoreaction-induced DNA strand displacement and T7 Exonuclease (T7 Exo)-assisted protein cyclic enzymatic amplification for ultrasensitive detection of cystatin C was described. Herein, Au@Fe3O4 as magnetic separator was labeled by antibody 1-conjungated DNA (DNA1) and the DNA substrate of T7 Exo (DNA3) which initially hybridized with output DNA (S1) to form a stable S1/DNA1 duplex (S1/DNA3). Antibody 2 was labeled by competing DNA (DNA 2). In the presence of cystatin C, sandwich immunoreaction would induce proximity hybridization between DNA2 and DNA3 and thus displace S1 from the S1/DNA3 duplex with formation of a stable DNA2/DNA3 duplex, realizing the conversion of input target cystatin C into output S1. To enhance the conversion ratio, the DNA2/DNA3 duplex was then digested by T7 Exo with release of DNA2 which could act as competing DNA again to displace S1 from the S1/DNA3 duplex in adjacent locations and initiate another cleavage reaction. Through such a cyclic process, each input cystatin C could induce more than one output S1, enhancing detection sensitivity. A hairpin DNA modified electrode was used to capture the output S1, and then, a hybridization chain reaction is triggered on the biosensor surface. Then, thionine as electron mediator was embedded into the dsDNA polymers to produce a detection signal. The electrochemical biosensor exhibited a much wider linear range of 0.01 pg mL–1 to 30 ng mL–1 with low detection limit of 3 fg mL–1. Moreover, this method introduced protein unrelated to nucleic acids into the realm of potential inputs for translation, which might create a new immunoassay method for sensitive detection of protein.

In this work, an electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of mucin-1 (MUC1) was designed with N-(aminobutyl)-N-(ethylisoluminol) (ABEI) and host-guest inclusion functionalized Platinum@Copperhierarchicaltrigonalbipyramidnanoframes(Pt@Cu HNFs) as signal label. At First, Pt@Cu HNFs were prepared to load abundant amine-modified β-cyclodextrin (β-CD) and luminophore ABEI via Pt-N bond. Based on the effect of host-guest recognition, ferrocenecarboxylic acid (FCA) as a catalyst of ABEI-H2O2 system was linked on the cavity of amine-modified β-CD to form nanocomposite of Pt@Cu HNFs-ABEI-(β-CD-FCA). Both Pt@Cu HNFs and FCA could catalyze H2O2 decomposition, which significantly enhanced the ECL intensity of ABEI-H2O2 system. Forthermore, simultaneously immobilizing ABEI and its catalyst FCA on Pt@Cu HNFs with good electrical conductivity could greatly increase the electron transfer efficiency in the ECL reaction, leading to a further signal amplification. Then, due to its good biocompatibility, large specific surface area and high luminous efficiency, the obtained Pt@Cu HNFs-ABEI-(β-CD-FCA) could act as an ideal nanocarrier of detection antibody (Ab2). As a result, a desirable “signal-on” ECL immunosensor was proposed for the detection of MUC1 with a wide linear range from 1 × 10−5 ng mL−1 to 10 ng mL−1 and a relatively low detection limit of 3.3 fg mL−1 (S N−1 = 3), making this approach hold great potential for protein analysis.

Herein, we report a moderate and simple approach to synthesize nickel phosphide nanorods on nickel foam (Ni2P/NF), which was employed as anode material for lithium ion batteries (LIBs). In this paper, interconnected Ni2P nanorods were fabricated through hydrothermal treatment of NF and subsequently by high temperature phosphating. NF is not only regarded as nickel source and metal current collector, but also as a support to grow electro-active material (Ni2P). Therefore, Ni2P/NF could act as a self-supported working electrode for LIBs without any extra addition of cohesive binders. Moreover, benefiting from the conductive capacity of Ni2P/NF, the active compound behaved superior lithium storage performance and cycling reversibility during electrochemical cycling process. The Ni2P/NF delivered excellent reversibility of 507 mAh g−1 at the current density of 50 mA g−1 after 100 cycles. This work may provide a potential method for preparation of metal phosphides as promising materials for LIBs, hydrogen evolution reaction (HER) or other fields.

•A nanohybrid of platinum nanoparticles-porous ZnO spheres-hemin was synthesized.•Hemin was adsorbed onto Pt–pZnO by ester-like binding between hemin and ZnO.•Alkaline phosphatase catalyzed 1-naphthyl phosphate and in situ produce electroactive substance 1-naphthol.•Pt–pZnO–hemin exhibited electrocatalytic activity toward 1-naphthol.In this work, a nanohybrid of platinum nanoparticles-porous ZnO spheres-hemin (Pt–pZnO–hemin) was synthesized for construction of alkaline phosphatase-based immunosensor for detection of influenza. Briefly, porous ZnO spheres (pZnO) were prepared using soluble starches as the capping agent, followed by surface functionalization of platinum nanoparticles via a hydrothermal method (Pt–pZnO). Then, hemin with carboxylic functionality was spontaneously adsorbed onto Pt–pZnO by ester-like binding between carboxylic group of hemin and ZnO. Compared with platinum nanoparticles and hemin, the resulting Pt–pZnO–hemin nanohybrid showed more excellent electrocatalysis activity toward 1-naphthol (1-NP). Taking advantage of the Pt–pZnO–hemin, we have developed an amplified electrochemical immunosensor based on in situ generation of redox probe by alkaline phosphatase (ALP) and Pt–pZnO–hemin as signal enhancer. Herein, electrochemically active 1-NP was generated by enzymatic hydrolysis of inactive 1-naphthyl phosphate by ALP, then Pt–pZnO–hemin was used as catalyst to catalytically oxidize 1-NP, resulting in electrochemical signal amplification. Furthermore, in comparison with other nanomaterials including Au–pZnO, Pt–pZnO and Au–pZnO–hemin, the excellent catalytical property of Pt–pZnO–hemin make it a promising nanohybrid material for ALP-based immunosensor for signal amplification.

•Synthesis of ABEI-Pd@AuNPs realized immobilization of ABEI without post-modification.•Grafting Fc on the surface of ABEI-Pd@AuNPs achieved effective signal amplification.•Simultaneously immobilizing ABEI and Fc contributed to good catalytic efficiency.•Pd@AuNPs could further enhance the ECL intensity due to their catalytic properties.In this work, N-(aminobutyl)-N-(ethylisoluminol) (ABEI), an analogue of luminol, is served as both the reductant and luminescence reagent to synthesize ABEI capped Pd@Au core-shell nanoparticles (ABEI-Pd@AuNPs). The nanoparticles not only exhibit inherent electrochemiluminescence (ECL) property, but also possess advantages of noble-metal nanomaterials such as outstanding electronic property, high specific surface area and good biocompatibility. In order to enhance the luminescence efficiency, ferrocene monocarboxylic acid (Fc) as catalyzer is grafted on the surface of ABEI-Pd@AuNPs with the aid of l-cysteine (l-Cys). When the Fc is electrochemically oxidized to ferricinium cation species (Fc+), the decomposition of H2O2 which existed in detection solution can be catalyzed by Fc+ to generate oxygen-related free radicals, resulting effective signal amplification for ABEI-H2O2 system. For potential applications, the Pd@Au core-shell nanoparticles bifunctionalized by ABEI and catalyzer are employed as nano-carriers to immobilize detection antibody (Ab2). Based on sandwiched immunoreactions, a “signal-on” ECL immunosensor is developed for detection of human collagen type IV (Col IV), a potential biomarker associated with diabetic nephropathy. Consequently, the proposed immunosensor provides a wide linear detection ranging from 1 pg mL−1 to 10 ng mL−1 with a relatively low detection limit of 0.3 pg mL−1 (S/N=3).

•NanoCoPC decorated MWCNTs was synthesized.•Detection signal is based on the redox property nanoCoPc without introduction other redox mediator.•A pseudobienzyme amplified strategy was based on electrocatalytic of nanoCoPc and catalytic activity of choline oxidase.In this work, cobalt phthalocyanine nanoparticles (nanoCoPc) functionalized multi-wall carbon nanotubes (MWCNTs) (nanoCoPc-MWCNTs) were synthesized to construct a sandwich-type electrochemical immunosensor for sensitive detection of procalcitonin (PCT). Herein, the electrochemical signal could directly originate from nanoCoPc-MWCNTs without the addition or labeling of other redox mediators. Moreover, a pseudobienzyme system based on catalytic activity of nanoCoPc and choline oxidase (ChOx) was constructed to enhance sensitivity. In the presence of choline, ChOx catalyzed the oxidation of choline with the production of H2O2, which was then oxidized by nanoCoPc-MWCNT with the improved electron transfer from Co (II) to Co (I), resulting in electrochemical signal amplification. In addition, MWCNTs with a large area surface and excellent electric conductivity were used as matrix for loading nanoCoPc and immobilizing bimolecular, which also amplified electrochemical signal. With above amplification strategy, the proposed immunosensor exhibited desirable performance for PCT with a wide linearity in the range from 0.01 to 100 ng mL−1 and a low detection limit of 1.23 pg mL−1.

A novel electrochemiluminescent (ECL) signal tag of Au nanoparticles capped by 3,4,9,10-perylene tetracarboxylic acid-thiosemicarbazide functionalized C60 nanocomposites (AuNPs/TSC-PTC/C60NPs) was developed for thrombin (TB) aptasensor construction based on the peroxydisulfate/oxygen (S2O82−/O2) system. For signal tag fabrication, the C60 nanoparticles (C60NPs) were prepared and then coated with 3,4,9,10-perylene tetracarboxylic acid (PTCA) by π–π stacking interactions. Afterwards, thiosemicarbazide (TSC) was linked with PTCA functionalized C60NPs via amidation for further assembling Au nanoparticles (AuNPs). Finally, detection aptamer of thrombin (TBA 2) was labeled on the ECL signal amplification tag of AuNPs/TSC-PTC/C60NPs. Herein, TSC, with the active groups of –NH2 and –SH, was selected and introduced into the ECL S2O82−/O2 system for the first time, which could not only offer the active groups of –SH to absorb AuNPs for TBA 2 anchoring but also remarkably enhance the ECL signal of the S2O82−/O2 system by the formation of TSC-PTC/C60NPs for signal amplification. Meanwhile, the sensing interface of a glassy carbon electrode (GCE) was modified by AuNPs/graphene (AuNPs/GR) nanocomposites with the large specific surface area and the active sites, followed by immobilization of thiol-terminated thrombin capture aptamer (TBA 1). With the formation of the sandwich-type structure of TBA 1, TB, and TBA 2 signal probes, a desirable enhanced ECL signal was measured in the testing buffer of an S2O82−/O2 solution for detecting TB. The aptasensor exhibited a good linear relationship for TB detection in the range of 1 × 10−5–10 nM with a detection limit of 3.3 fM.

A new type of multifunctional metal–organic framework (MOF) has been synthesized by encapsulating hemin into the nano-sized Fe-MIL-88 MOFs (hemin@MOFs) and first applied in an electrochemical aptasensor to detect thrombin (TB) with the aid of an enzyme for signal amplification. The gold nanoparticle functionalized hemin@MOFs (Au/hemin@MOFs) have not only simultaneously served as redox mediators and solid electrocatalysts, but have also been utilized as an ideal loading platform to immobilize a large number of biomolecules. In this aptasensor, Au/hemin@MOFs conjugated with glucose oxidase (GOD) and thrombin binding aptamer (TBA II) were used as the secondary aptamer bioconjugates (Au/hemin@MOF–TBA II–GOD bioconjugates), and TB was sandwiched between Au/hemin@MOF–TBA II–GOD bioconjugates and the amino-terminated TBA I which was self-assembled on the gold nanoparticle (AuNP) modified electrode. The GOD could oxidize glucose into gluconic acid accompanied by the generation of H2O2. The generated H2O2 on the electrode surface was further electrocatalyzed by hemin@MOFs to amplify the electrochemical signal of hemin contained in hemin@MOFs. Therefore, the synthesized hemin@MOFs represented a new paradigm for multifunctional materials since it combined three different functions including serving as catalysts, redox mediators and loading platforms within a single material. With such an ingenious design, a wide linear range of 0.0001 nM to 30 nM was acquired with a relatively low detection limit of 0.068 pM for TB detection.

A novel redox probe 3,4,9,10-perylenetetracarboxylic acid/o-phenylenediamine (PTCA/OPD) with well-defined redox peaks caused by the synergistic action between them was demonstrated via theoretical and practical research, and applied in an electrochemical aptasensor to detect thrombin (TB) based on an Fe3O4 magnetic bead (MB) as a nonenzymatic catalyst.

In this work, a new electrochemical biosensor based on catalyzed hairpin assembly target recycling and cascade electrocatalysis (cytochrome c (Cyt c) and alcohol oxidase (AOx)) for signal amplification was constructed for highly sensitive detection of microRNA (miRNA). It is worth pointing out that target recycling was achieved only based on strand displacement process without the help of nuclease. Moreover, porous TiO2 nanosphere was synthesized, which could offer more surface area for Pt nanoparticles (PtNPs) enwrapping and enhance the amount of immobilized DNA strand 1 (S1) and Cyt c accordingly. With the mimicking sandwich-type reaction, the cascade catalysis amplification strategy was carried out by AOx catalyzing ethanol to acetaldehyde with the concomitant formation of high concentration of H2O2, which was further electrocatalyzed by PtNPs and Cyt c. This newly designed biosensor provided a sensitive detection of miRNA-155 from 0.8 fM to 1 nM with a relatively low detection limit of 0.35 fM.Keywords: cascade catalysis; dual signal amplification; microRNA; target catalyzed hairpin assembly

An alkaline phosphatase (ALP)-based biosensor can in situ generate an electroactive product by enzymatic hydrolysis of inactive substrates. To obtain a higher signal-to-background ratio, a chemical redox cycling signal-amplified strategy based on the addition of a strong reducing agent has often be applied in the construction of ALP-based biosensors. However, the strong reducing agent not only affects the activity of ALP but also readily reacts with dissolved oxygen, leading to inaccurate results. In this work, a new signal-amplified strategy for a thrombin (TB) aptasensor based on the catalytic oxidation of ALP-generated products, 1-naphthol (NP), using hemin/G-quadruplex DNAzymes was reported. We implemented gold-nanoparticle-decorated zinc oxide nanoflowers (Au-ZnO) as the matrix for immobilizing ALP and TB aptamer (TBA) and then labeled it with hemin to form hemin/G-quadruplex/ALP/Au-ZnO bioconjugates (TBA II bioconjugates). Through a “sandwich” reaction, TBA II bioconjugates were captured on the electrode surface. The amplified signal was carried out in two steps: (i) an ALP-catalyzed inactive substrate, 1-naphthyl phosphate (NPP), in situ produces NP on the surface of the electrode; (ii) on the one hand, NP as a new reactant could be directly electrooxidized and generated an electrochemical signal, but, on the other hand, NP could be oxidized by hemin/G-quadruplex in the presence of H2O2, resulting in amplification of the electrochemical signal. The proposed TB aptasensor achieved a linear range of 1 pM to 30 nM with a detection limit of 0.37 pM (defined as S/N = 3).Keywords: alkaline phosphatase; catalytic oxidation of 1-naphthol; hemin/G-quadruplex; signal-amplified aptasensor;

In this work, we have demonstrated a novel electrochemical method based on target-induced cleavage of a specific peptide for sensitive analysis of prostate specific antigen (PSA) by using silver enhancement. First, multiwalled carbon nanotubes/poly(amidoamine) dendrimers (MWCNTs–PAMAM) nanohybrids were assembled on the electrode to bind the peptide. Subsequently, dithiobis(succinimidylpropionate) (DSP)@Au@SiO2 was prepared as a tracing tag and covalent bond with the peptides via the inherent interaction between DSP and the amino of peptide. In the presence of PSA, the peptide was specifically recognized and cleaved, resulting in the loss of the tracing tag in electrode surface. Thereafter, silver enhancement was performed on the left DSP@Au@SiO2 nanohybrids. The electrochemical stripping signal of the deposited silver was used to monitor this process. Under optimal conditions, the proposed biosensor achieved a wide line from 0.001 to 30 ng mL–1 with a detection limit of 0.7 pg mL–1. This work demonstrated the combination of the direct transduction of peptide cleavage events with the highly sensitive silver enhancement method, providing a promising effective strategy for PSA detection.Keywords: Ag deposition; dithiobis(succinimidylpropionate) (DSP)@Au@SiO2; electrochemical biosensor; multiwalled carbon nanotubes/poly(amidoamine) dendrimers; peptide; prostate specific antigen;

In this study, an off–on switching of a dual amplified electrochemiluminescence (ECL) biosensor based on Pb2+-induced DNAzyme-assisted target recycling and rolling circle amplification (RCA) was constructed for microRNA (miRNA) detection. First, the primer probe with assistant probe and miRNA formed Y junction which was cleaved with the addition of Pb2+ to release miRNA. Subsequently, the released miRNA could initiate the next recycling process, leading to the generation of numerous intermediate DNA sequences (S2). Afterward, bare glassy carbon electrode (GCE) was immersed into HAuCl4 solution to electrodeposit a Au nanoparticle layer (depAu), followed by the assembly of a hairpin probe (HP). Then, dopamine (DA)-modified DNA sequence (S1) was employed to hybridize with HP, which switching off the sensing system. This is the first work that employs DA to quench luminol ECL signal, possessing the biosensor ultralow background signal. Afterward, S2 produced by the target recycling process was loaded onto the prepared electrode to displace S1 and served as an initiator for RCA. With rational design, numerous repeated DNA sequences coupling with hemin to form hemin/G-quadruplex were generated, which could exhibit strongly catalytic toward H2O2, thus amplified the ECL signal and switched the ON state of the sensing system. The liner range for miRNA detection was from 1.0 fM to 100 pM with a low detection limit down to 0.3 fM. Moreover, with the high sensitivity and specificity induced by the dual signal amplification, the proposed miRNA biosensor holds great potential for analysis of other interesting tumor markers.

Graphene quantum dots (GQDs) with an average diameter as small as 2.3 nm were synthesized to fabricate an electrochemiluminescence (ECL) biosensor based on T7 exonuclease-assisted cyclic amplification and three-dimensional (3D) DNA-mediated silver enhancement for microRNA (miRNA) analysis. Herein, to overcome the barrier in immobilizing GQDs, aminated 3,4,9,10-perylenetetracarboxylic acid (PTCA–NH2) was introduced to load GQDs through π–π stacking (GQDs/PTCA–NH2), realizing the solid-state GQDs application. Furthermore, Fe3O4–Au core–shell nanocomposite (Au@Fe3O4) was adopted as a probe anchor to form a novel electrochemiluminescent signal tag of GQDs/PTCA–NH2/Au@Fe3O4. The prepared ECL signal tag was decorated on the electrode surface, exhibiting excellent film-forming performance, good electronic conductivity, and favorable stability, all of which overcame the obstacle for applying GQDs in ECL biosensing and showed a satisfactory ECL response under the coreactant of S2O82– (peroxydisulfate). Afterward, hairpin probe modified on the electrode was opened by helper DNA, followed by assembling target to hybridize with the exposed stem of the helper DNA. Significantly, T7 exonuclease was employed to digest the DNA/RNA duplex and trigger the target recycling without asking for a specific recognition site in the target sequence, realizing a series of RNA/DNA detections by changing the sequence of the complementary DNA. At last, the ECL signal was further enhanced by silver nanoparticles (AgNPs)-based 3D DNA networks. After the two amplifications, the ECL signal of GQDs was extraordinarily increased and the prepared biosensor achieved a high sensitivity with the detection limit of 0.83 fM. The biosensor was also explored in real samples, and the result was in good accordance with the performance of quantitative real-time polymerase chain reaction (qRT-PCR). Considering the excellent sensitivity and applicability, we believe that the proposed biosensor is a potential candidate for nucleic acid biosensing.

The self-enhanced electrochemiluminescence (ECL) with high sensitivity could be an effective method for anticancer drug screening with cell apoptosis monitoring. Here we reported an ultrasensitive ECL cytosensor for cell apoptosis monitoring by using self-enhanced electrochemiluminescent ruthenium–silica composite nanoparticles (Ru–N–SiNPs) labeled annexin V as signal probes. The Ru–N–SiNPs were first synthesized through simple hydrolysis of a novel precursor containing luminescent and intracoreactant groups in one molecule, which presented higher emission efficiency and enhanced ECL intensity due to the shorter electron-transfer path and less energy loss. Moreover, the as-proposed ECL cytosensor was successfully used to investigate efficiency of paclitaxel toward MDA-MB-231 breast cancer cell in the range from 1 nM to 200 nM with a detection limit of 0.3 nM and a correlation coefficient of 0.9917. The improved accuracy and excellent dynamic range revealed the potential applications in biomolecules diagnostics and cells detections, especially in living and complex systems.

A highly sensitive electrochemiluminescent (ECL) aptasensor was constructed using semicarbazide (Sem) as co-reaction accelerator to promote the ECL reaction rate of CdTe quantum dots (CdTe QDs) and the co-reactant of peroxydisulfate (S2O82–) for boosting signal amplification. The co-reaction accelerator is a species that when it is introduced into the ECL system containing luminophore and co-reactant, it can interact with co-reactant rather than luminophore to promote the ECL reaction rate of luminophore and co-reactant; thus the ECL signal is significantly amplified in comparison with that in which only luminophore and co-reactant are present. In this work, the ECL signal probes were first fabricated by alternately assembling the Sem and Au nanoparticles (AuNPs) onto the surfaces of hollow Au nanocages (AuNCs) via Au–N bond to obtain the multilayered nanomaterials of (AuNPs-Sem)n-AuNCs for immobilizing amino-terminated detection aptamer of thrombin (TBA2). Notably, the Sem with two -NH2 terminal groups could not only serve as cross-linking reagent to assemble AuNPs and AuNCs but also act as co-reaction accelerator to enhance the ECL reaction rate of CdTe QDs and S2O82– for signal amplification. With the sandwich-type format, TBA2 signal probes could be trapped on the CdTe QD-based sensing interface in the presence of thrombin (TB) to achieve a considerably enhanced ECL signal in S2O82– solution. As a result, the Sem in the TBA2 signal probes could accelerate the reduction of S2O82– to produce the more oxidant mediators of SO4•–, which further boosted the production of excited states of CdTe QDs to emit light. With the employment of the novel co-reaction accelerator Sem, the proposed ECL biosensor exhibited ultrahigh sensitivity to quantify the concentration of TB from 1 × 10–7 to 1 nM with a detection limit of 0.03 fM, which demonstrated that the co-reaction accelerator could provide a simple, efficient, and low-cost approach for signal amplification and hold great potential for other ECL biosensors construction.

Traditionally, amplified DNA detection in a loop-mediated isothermal amplification (LAMP) was carried out in a complicated gel electrophoresis or with expensive fluorescence-based methods. Here, instead of direct detection that relies on amplified DNA, the indirect detection based on tracing phosphate ions (Pi) generated during LAMP by using an electrochemical method has been proposed for sensitive nucleic acid detection. Pyrophosphate (PPi) as the byproduct of nucleic acid polymerization reaction in LAMP was hydrolyzed into Pi by the preaddition of thermostable inorganic pyrophosphatase (PPase). Thus, the total amount of Pi in the LAMP-amplified sample was proportional to the amount of starting DNA templates. The obtained Pi could then react with acidic molybdate to form the molybdophosphate precipitates on the electrode surface, which serve as redox mediators to give a readily measurable electrochemical signal. The practicality of this strategy has been further demonstrated by employing it for sensitive and accurate quantification of Nosema bombycis genomic DNA PTP1. The electrochemical method allowed the quantitative analysis for target genomic DNA with a detection limit of 17 fg/μL. Thus, we suppose that the novel method proposed in this work with superior sensitivity and specificity, as well as the simple feature, can be easily established for quantitative analysis of many other kinds of nucleic acids in the assistance of LAMP.

To remedy the problems caused by the introduction of an additional electron mediator and realize signal amplification, a new strategy has been presented to construct an electrochemical aptasensor for thrombin detection based on the cascade electrocatalysis of alkaline phosphatase (ALP) and Pt nanoparticle (PtNP)-functionalized ZnO nanoflowers.

A simple electrochemical immunosensor for determination of Streptococcus suis serotype 2 (SS2) is presented. Nickel hexacyanoferrate nanoparticles (NiHCFNPs) and gold nanocages (AuNCs) were combined together through complexation between the cyanide (CN−) and gold ions, and acted as a carrier for immobilization of the detection antibody (Ab2). The capture antibody (Ab1) was combined by a protein A (PA) and gold nanoparticle (AuNP) modified electrode. In a sandwich-type immunoassay mode, ascorbic acid (AA) was added to the base solution and its oxidation was catalyzed by the AuNCs–NiHCFNPs complex to greatly amplify the response signal. The resulting immunosensor exhibited excellent selectivity and sensitivity, with a linear concentration range of 0.0005–80 ng mL−1 and a detection limit of 0.15 pg mL−1.

A nanohybrid based on reduced graphene oxide functionalized by poly(amido-amine), multi-walled carbon nanotubes and Au nanoparticles (RGO–PAMAM–MWCNT–AuNPs) for simultaneous electrochemical determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) was reported in this paper. The RGO–PAMAM–MWCNT–AuNP-modified electrode showed a high selectivity towards the oxidation of AA, DA, and UA, and resolved their overlapped oxidation peaks into three well-defined peaks. The RGO–PAMAM–MWCNT–AuNP nanohybrids were characterized by scanning electron microscopy (SEM). Several important parameters that control the performance of the electrochemical sensor were investigated and optimized. Under optimal conditions by a differential pulse voltammetry (DPV) method, the linear response ranges for the determination of AA, DA, and UA are 20 μM to 1.8 mM, 10 μM to 0.32 mM, and 1 μM to 0.114 mM in the co-existence systems, respectively. The corresponding detection limits are 6.7 μM, 3.3 μM and 0.33 μM (S/N = 3), respectively.

•ZNs-PAMAM nanocomposites could be used to immobilize numerous luminol molecules.•ECL efficiency of luminol could be improved by immobilizing luminol on the electrode.•Using ECL technique to detect CA15-3 shows promise in high sensitivity and rapid detection.In this study, we constructed a novel electrochemiluminescence (ECL) immunosensor for sensitive and selective detection of carbohydrate antigen 15-3 (CA15-3) by using polyamidoamine (PAMAM)-functionalized ZnO nanorods (ZNs-PAMAM) as carriers. PAMAM dendrimers with hyper-branched and three-dimensional structure were used as linked reagents for co-immobilization of luminol and CA15-3 detection antibody on the ZNs to prepare the signal probe. In addition, ZNs could hasten the decomposition of H2O2 to generate various reactive oxygen species (ROSs) which accelerated the ECL reaction of luminol with amplified ECL intensity. Compared with luminol in the detection solution, the ECL efficiencies of luminol could be improved by immobilizing luminol on the electrode due to the smaller distance between luminescence reagent and the electrode surface. Moreover, the electrodepositing gold nanoparticles (AuNPs) on the bare glass carbon electrode (GCE) with enhanced surface area could capture a large amount of primary anti-CA15-3 to improve the sensitivity of the immunosensor. Under the optimized experimental conditions, a wide linear range of 0.1–120 U mL−1 was acquired with a relatively low detection limit of 0.033 U mL−1 (S/N=3) for CA15-3.

•Au nanoparticles functionalized porous graphene oxide (Au-PGO) was prepared and introduced as a sensing platform.•Au@Pd core/shell bimetallic functionalized graphene nanoparticles (Au@Pd-Gra) as signal label application for immunosensor was first reported.•A sandwich electrochemical immunosensor for Carbohydrate antigen 19-9 detection was developed.A facile and feasible sandwich-type electrochemical immunosensor for ultrasensitive determination of Carbohydrate antigen 19-9 (CA19-9) was designed by using Au nanoparticles functionalized porous graphene (Au-PGO) as sensing platform and Au@Pd core/shell bimetallic functionalized graphene nanocomposites (Au@Pd-Gra) as signal enhancers. Herein, Au@Pd-Gra with a large surface area was prepared for immobilizing plentiful of redox probe-thionine (Thi), horseradish peroxidase (HRP) and secondary antibodies (Ab2), leading to the formation of Au@Pd-Gra/Thi-Ab2/HRP bioconjugate which exhibited satisfying electrochemical redox activity, high electrocatalytic activity and friendly biocompatibility. With the synergistic effect between Au@Pd-Gra and HRP, almost triple amplified detection signal was achieved in the presence of H2O2, so as to improve the detection limit of the proposed immunosensor effectively. Furthermore, Au-PGO was utilized as the biosensor platform which could greatly enhance the surface area to immobilize a large amount of captured primary antibodies (Ab1) leading a further enhancement in the sensitivity of immunosensor. Under optimal conditions, the electrochemical immunosensor exhibited desirable performance for determination of CA19-9 with a wide linearity in the range from 0.015 to 150 U mL–1 and a relatively low detection limit of 0.006 U mL–1. Importantly, the resulted immunosensor displayed good specificity and high sensitivity, implying potential applications in clinical research.

•PEI-rGO acts as co-reactant and immobilized platform in the same time, which simplifies the preparation of the sensor.•AuNPs-PAMAM can effectively immobilize a large number of the antibody and dramatically enhance the ECL signal.•The immunosensor for AFP detection exhibits high sensitivity, good stability and satisfying selectivity.In this study, a novel solid-state Ru(bpy)32+ electrochemiluminescence (ECL) sandwiched immunosensor for sensitive detection of α-fetoprotein (AFP) was constructed based on poly(ethylenimine) (PEI) functionalized reduced graphene oxide (PEI-rGO) and Au nanoparticles (AuNPs) decorated polyamidoamine (PAMAM) dendrimers. Both PEI and PAMAM are polymers with a lot of amino groups, which are able to serve as good co-reactant to remarkably enhance the ECL signal of Ru(bpy)32+. For improving the poor conductivity of PAMAM, the AuNPs were decorated on the amino groups of PAMAM. Through Au-N bonds, the formed AuNPs-PAMAM was decorated on the PEI-rGO. The obtained AuNPs-PAMAM/PEI-rGO was introduced to immobilize the detection antibody (Ab2). Then, the Ab2 labeled AuNPs-PAMAM/PEI-rGO was modified onto the glass carbon electrode surface via sandwiched immunoreactions. The ECL substrate was prepared by mixing nafion and the complex (Ru-PtNPs) of Pt nanoparticles (PtNPs) and Ru(bpy)32+, which could reduce the consumption of Ru complex, simplify the operation and enhance the ECL efficiency. The experimental results demonstrated that the proposed immunosensor had good response to AFP. The linear range was from 0.01 pg mL−1 to 10 ng mL−1 with a low detection limit of 3.3 fg mL−1. Meanwhile, with satisfying stability, selectivity and reproducibility, the proposed sandwiched immunosensor was presented to possess good potential in clinical detection.

•PAMAM−NFLX, a novel co-reactant, could efficiently amplify ECL signal of S2O82--O2.•Pd−Au core−shell HOHs were used to assemble Ab2 and PAMAM-NFLX.•Pd−Au core−shell HOHs could further amplify the ECL signal.In this work, a novel polyamidoamine-norfloxacin (PAMAM-NFLX) complex and core–shell Pd–Au hexoctahedrons (Pd@Au HOHs) as enhancers are employed for development of a sensitive sandwich-type electrochemiluminescence (ECL) immunosensor to detect thyroid stimulating hormone (TSH). Here, norfloxacin (NFLX) is decorated abundantly on the surface of polyamidoamine (PAMAM) dendrimer via amide linkage to form PAMAM-NFLX complex. Thus, the resultant PAMAM-NFLX can serve as a novel co-reactant to efficiently amplify the ECL signal of peroxydisulfate-oxygen (S2O82−-O2) system. Pd@Au HOHs were used as nano-carriers to assemble detection antibody (Ab2) and the PAMAM-NFLX complex. Besides, it can further enhance the ECL signal by promoting the generation of intermediate free radical HO• during the ECL reaction of S2O82−-O2 system. The proposed immunosensor shows high sensitivity and specificity, and responds linearly to the concentration of TSH from 0.05 to 20 μIU mL−1 with a low detection limit of 0.02 μIU mL−1 (S/N=3). Moreover, the immunosensor successfully achieves the detection of TSH in practical human blood serum with desirable results.

•A simple and time-saving method of Lu–AuNPs@Fe3O4 preparation is developed.•Lu–AuNPs@Fe3O4 is used as ECL signal label and enhancer.•A sandwiched MUC1 immunosensor is constructed with a detection limit of 4.5 fg/mL.In this work, a novel and multifunctional nanocomposite of luminol capped gold modified Fe3O4 (Lu–AuNPs@Fe3O4) was utilized as the carrier of secondary antibody (Ab2) to fabricate a sandwiched electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of mucin-1 (MUC1). Herein, the luminol capped gold nanoparticles (Lu–AuNPs) were synthesized with HAuCl4 and luminol by the help of NaBH4 at room temperature, and then Lu–AuNPs were adsorbed on the Fe3O4 magnetic nanoparticles (MNPs) to form the nanocomposite of Lu–AuNPs@Fe3O4 via electrostatic interaction. Fe3O4 MNPs in Lu–AuNPs@Fe3O4 exhibited excellent conductivity and admirable catalytic activity in H2O2 decomposition, which could enhance the ECL efficiency of luminol–H2O2 system. In addition, the substrates of gold coated ZnO nanoparticles (AuNPs@ZnO), providing large specific surface areas for primary antibody (Ab1) capturing, were modified on the electrode. As a result, a wide linear range of 7 orders of magnitude from 10 fg/mL to 10 ng/mL was obtained with an ultralow detection limit of 4.5 fg/mL for MUC1.

•ALP catalyzed p-NPP hydrolysis and in situ produce electroactive substance.•Pt/CeO2/GO were used to oxide 1-naphthol, resulting in signal amplification.•GO and Pt were used to functionalized CeO2 to improveits properties.•Pt/CeO2/GO with a large of area increased the immobilized amount of ALP and Ab2.In this work, an amplified electrochemical immunosensor based on 1-naphthol as electroactive substance and Pt/CeO2/GO composites as catalytic amplifier was constructed for sensitive detection influenza. Through “sandwich” reaction, the Pt/CeO2/GO functionalized bioconjugates were captured on electrode surface and the electrochemical signal directly originated from 1-naphthol, which was in situ produced with high local concentration though the hydrolysis of 1-naphthyl phosphate catalyzed by ALP. Then, 1-naphthol as new reactant was oxidized by Pt/CeO2/GO composites with outstanding catalytic performance, resulting in detection signal amplification. In addition, as compared to label electroactive substance to antibodies, a simplified preparative step of immunosensor could be achieved because the signal probe get rid of introducation other electroactive substances. The proposed immunosensor achieved a linear range of 1.0×10−3–1.0 ng mL−1 and 5.0 to 1.0×102 ng mL−1 with a detection limit of 0.43 pg mL−1 (defined as S/N=3).

•LNT is used as a green stabilizer and reducing agent to synthesize PdNWs.•PAMAM–Ru, a self-enhanced ECL derivative, is prepared.•The self-enhanced ECL derivative has high luminous stability and efficiency.•The immunosensor has good sensitivity, stability, selectivity and reproducibility.Co-reactant electrochemiluminescence (ECL) is a simple and effective method for sensitive detection with amplified ECL signals. However, the intermolecular interaction between the luminescent reagents and their corresponding co-reactants, which is widely applied, has disadvantages in poor stability, low efficiency of electron transfer and relatively high loss of energy. In this work, an intramolecular self-enhanced ECL is proposed to settle this problem. Firstly, palladium nanowires (PdNWs) are synthesized with a green procedure in which Lentinan (LNT), one of β-glucans with a triple helical conformation (t-LNT) in aqueous solution and single chains (s-LNT) at a temperature higher than 130 °C, is used as stabilizer and reducing agent. The abtined PdNWs are applied to immobilize polyamidoamine (PAMAM) dendrimer which further reacts with tris (4, 4′-dicarboxylicacid-2, 2′-bipyridyl) ruthenium (II) dichloride to form a new electrochemiluminescent derivative (PdNWs–PAMAM–Ru). In this way, the Ru (II) luminophore and its co-reactive groups (amine groups in PAMAM) exist in the same complex, by which the electronic transmission distance is shortened and the luminous properties including stability and efficiency are enhanced. Moreover, due to the high specific surface areas and good electro-catalytic ability of PdNWs, the obtained PdNWs–PAMAM–Ru can be also applied to immobilize detection antibody (Ab2). Then, a sandwiched and sensitive ECL immunosensor is fabricated for the detection of carcinoembryonic antigen (CEA) with a wide linear ranged from 0.001 ng mL−1 to 80 ng mL−1 and a low detection limit of 0.3 pg mL−1.

•Simultaneous detection of four biomarkers in one electrode surface.•One-step codeposition of graphene/gold as the base substrate.•Using HCR, B/SA and AuNPs based nanomaterials for signal amplification.•Using four kinds of redox probes as identification tags.•The immunosensor was very simple, quick and highly sensitive.A sandwich-type electrochemical immunosensor based on redox probe tags identification technology for ultrasensitive simultaneous detection of four antigens was proposed. In this project, well-distributed graphene/gold (GR–Au) hybrid film was acquired through one-step codeposition in an electrode surface and served as the base substrate for immobilizing capture antibodies (Ab1). Hybridization chain reaction (HCR) and biotin/streptavidin (B/SA), combining with gold magnetic nanoparticles were applied to increase the immobilization amount of signal tags in detection antibody (Ab2) bioconjugates. To verify this strategy, four representative biomarkers, a-fetoprotein (AFP), carcinoembryonic antigen (CEA), carbohydrate antigen (CA)125 and prostate special antigen (PSA), were used as model analytes. The resulting immunosensor could simultaneously detect four antigens in single-pass differential pulse voltammetry (DPV) scan, and exhibited obviously improved senstivity compared to previous similar immunosensors, displayed good linear relationships in the ranges from 0.2 to 800 pg/mL for AFP, 0.2 to 600 pg/mL for CEA, 0.2 to 1000 pg/mL for CA125, 0.2 to 800 pg/mL for PSA and with detection limits of 62, 48, 77 and 60 fg/mL, respectively.

An intramolecular self-enhanced electrochemiluminescent derivative is prepared by grafting polystyrene (PS)-based polymer chains with pendant Ru(II) luminophore from poly(ethylenimine) (PEI) on the surface of palladium nanocages (PdNCs). In this way, the Ru(II) luminophore and its co-reactive group (amine groups in PEI) exist in the same polymer molecule, which shortens the electronic transmission distance between them and enhances the luminous stability. Meanwhile, through atom transfer radical polymerization (ATRP), the loading amount of Ru(II) luminophore is greatly increased. Therefore, the obtained electrochemiluminescent derivative (PdNC–PEI–PSRu) has high luminous efficiency and stability. Furthermore, due to their special nanostructures of porous walls and hollow interiors, PdNCs have great advantages in high specific surface areas and good electrocatalytic ability, which make them act as an excellent immobilized platform for PEI and detection antibody. Based on the sandwiched immunoreactions, a sensitive “signal on” electrochemiluminescence immunosensor is constructed for the detection of carbohydrate antigen 15-3 (CA 15-3). As a result, a wide linear range from 0.01 U mL−1 to 120 U mL−1 is acquired with a relatively low detection limit of 0.003 U mL−1.

Endotoxin, also known as lipopolysaccharide (LPS), is able to induce a strong immune response on its internalization into mammalian cells. To date, aptamer-based biosensors for LPS detection have been rarely reported. This work describes a new signal-on electrochemical aptasensor for the ultrasensitive detection of LPS by combining the three-way DNA hybridization process and nanotechnology-based amplification. With the help of DNA1 (associated with the concentration of target LPS), the capture probe hybridizes with DNA1 and the assistant probe to open its hairpin structure and form a ternary “Y” junction structure. The DNA1 can be released from the structure in the presence of nicking endonuclease to initiate the next hybridization process. Then a great deal of cleaved capture probe produced in the cyclic process can bind with DNA2–nanocomposite, which contains the electroactive toluidine blue (Tb) with the amplification materials graphene (Gra) and gold nanoparticles (AuNPs). Thus, an enhanced electrochemical signal can be easily read out. With the cascade signal amplification, this newly designed protocol provides an ultrasensitive electrochemical detection of LPS down to the femtogram level (8.7 fg mL−1) with a linear range of 6 orders of magnitude (from 10 fg mL−1 to 50 ng mL−1). Moreover, the high sensitivity and specificity make this method versatile for the detection of other biomolecules by changing the corresponding sequences of the capture probe and the assistant probe.

Here we show an amplification-coupled detection method for directly measuring released hydrogen ions during the loop mediated isothermal amplification (LAMP) procedure by using a pH meter. The genomic DNA of Nosema bombycis (N. bombycis) was amplified and detected by employing this LAMP-pH meter platform for the first time.

A multi-functional luminol-reduced Pt@Au hybrid flower-like nanocomposite (luminol–Pt@AuNF) which not only acts as an efficient signal probe but also constitutes a pseudobienzyme amplifying system with choline oxidase (ChOx) was firstly synthesized and applied to the construction of a solid-state luminol electrochemiluminescence (ECL) immunosensor for cardiac troponin I (cTnI) detection.

•A novel ECL acetylcholine biosensor was constructed based on AMs-AChE-ChO and dpGR-AuNPs-CS nanocomposites.•The biofunctional AMs-AChE-ChO biocomposite was unprecedentedly prepared.•By the catalysis of these nanocomposites, amplified ECL signal was obtained.•Biosensor response was linear from 6.7 nM to 0.92 mM ATCl with detection limit of 2.2 nM.•The biosensor exhibited excellent reproducibility, satisfying stability and good selectivity.A novel electrochemiluminescence (ECL) biosensing system was designed for the detection of acetylthiocholine chloride (ATCl) in this work. First, graphene-AuNPs-chitosan (GR-AuNPs-CS) nanocomposite, which possesses the property of intensification effect on the ECL of luminol, was electrochemically deposited on the bare GCE. Then, a biofunctional Fe3O4-TiO2-AChE-ChO biocomposite was unprecedentedly prepared which exhibited the mimic peroxidase activity of Fe3O4 and the enhancement effect of TiO2 on the ECL intensity of luminol. Subsequently, the substrate ATCl was hydrolyzed by AChE of AChE-ChO multiple enzymes to generate thiocholine, which was then catalyzed by ChO to produce H2O2in situ. H2O2, as the coreactant of luminol-ECL system can enhance the ECL intensity of luminol. On the basis of this principle and smart integration of the above nanocomposites under the optimal conditions, the resulting ECL biosensor for ATCl showed wide linear range from 6.7 nM to 0.92 mM with detection limit (signal-to-noise ratio of 3) of 2.2 nM. The excellent performance of the biosensor makes this biosensing system suitable and promising in the practical application of choline type of biomass.

•Pt–Pd nanowires were combined with pseudo triple-enzyme electrochemical aptasensor.•Pt–Pd nanowires served as signal enhancer.•Labeling process, deactivation and spatial distribution of enzymes were solved.Our present work aimed at developing a pseudo triple-enzyme cascade electrocatalytic electrochemical aptasensor for determination of thrombin with the amplification of alcohol dehydrogenase (ADH)-Pt–Pd nanowires bionanocomposite and hemin/G-quadruplex structure that simultaneously acted as NADH oxidase and HRP-mimicking DNAzyme. With the addition of ethanol to the electrolyte, the ADH immobilized on the Pt–Pd nanowires catalyzed ethanol to acetaldehyde accompanied by NAD+ being converted to NADH. Then the hemin/G-quadruplex firstly served as NADH oxidase, converting the produced NADH to NAD+ with the concomitant local formation of high concentration of H2O2. Subsequently, the hemin/G-quadruplex acted as HRP-mimicking DNAzyme, bioelectrocatalyzing the produced H2O2. At the same time, the Pt–Pd nanowires employed in our strategy not only provided a large surface area for immobilizing thrombin binding aptamer (TBA) and ADH, but also served as HRP-mimicking DNAzyme which rapidly bioelectrocatalyzed the reduction of the produced H2O2. Thus, such a pseudo triple-enzyme cascade electrochemical aptasensor could greatly promote the electron transfer of hemin and resulted in the dramatic enhancement of electrochemical signal. As a result, a wide dynamic concentration linear range from 0.2 pM to 20 nM with a low detection limit of 0.067 pM for thrombin (TB) determination was obtained. The excellent performance indicated that our strategy was a promising way for ultrasensitive assays in electrochemical aptasensors.

•We firstly inducted the hydrolysis reaction between SAHH and SAH into ECL system.•In situ generating l-Hcys greatly amplified the ECL signal.•In situ generated l-Hcys could gradually accumulate on the surface of the immunosensor.•The strategy has the advantages of sensitivity, good selectivity and reproducibility.In this work, an ultrasensitive peroxydisulfate electrochemiluminescence (ECL) immunosensor using in situ generation of l-homocysteine (l-Hcys) for signal amplification was successfully constructed for detection of carcinoembryonic antigen (CEA). In the reaction of biological methylation, S-adenosyl-l-homocysteine hydrolase (SAHH) catalyzed the reversible hydrolysis of S-adenosyl-l-homocysteine (SAH) to produce l-Hcys, which was inducted into ECL system to construct the immunosensor for signal amplification in this work. Simultaneously, Gold and palladium nanoparticles functionalized multi-walled carbon nanotubes (Au-PdNPs@MWCNTs) were prepared, which were introduced to immobilize the secondary antibody (Ab2) and SAHH with high loading amount and good biological activity due to their improved surface area and excellent biocompatibility. Then the proposed ECL immunosensor was developed by a sandwich-type format using Au-PdNPs@MWCNTs-SAHH-Ab2 as tracer and graphene together with AuNPs as substrate. Besides the enhancement of Au-PdNPs, the enzymatic catalysis reaction also amplified the ECL signal dramatically, which was achieved by efficient catalysis of the SAHH towards the hydrolysis of SAH to generate improved amount of l-Hcys in situ. Furthermore, due to the special interaction between Au-PdNPs and -SH or -NH2 in l-Hcys, l-Hcys would gradually accumulate on the surface of the immunosensor, which greatly enhanced the concentration of l-Hcys on the immunosensor surface and further improved the ECL intensity. With the amplification factors above, a wide linear ranged from 0.1 pg mL−1 to 80 ng mL−1 was acquired with a relatively low detection limit of 33 fg mL−1 for CEA.

•We presented an ultrasensitive detection system for small molecule ochratoxin A.•The loop-mediated isothermal amplification (LAMP) was employed here.•The LAMP amplicons were readout by an electrochemiluminescence detection system.•The quantitative analysis of OTA depended on the increase of ECL intensity.In this study, we for the first time presented an efficient, accurate, rapid, simple and ultrasensitive detection system for small molecule ochratoxin A (OTA) by using the integration of loop-mediated isothermal amplification (LAMP) technique and subsequently direct readout of LAMP amplicons with a signal-on electrochemiluminescent (ECL) system. Firstly, the dsDNA composed by OTA aptamer and its capture DNA were immobilized on the electrode. After the target recognition, the OTA aptamer bond with target OTA and subsequently left off the electrode, which effectively decreased the immobilization amount of OTA aptamer on electrode. Then, the remaining OTA aptamers on the electrode served as inner primer to initiate the LAMP reaction. Interestingly, the LAMP amplification was detected by monitoring the intercalation of DNA-binding Ru(phen)32+ ECL indictors into newly formed amplicons with a set of integrated electrodes. The ECL indictor Ru(phen)32+ binding to amplicons caused the reduction of the ECL intensity due to the slow diffusion of Ru(phen)32+–amplicons complex to the electrode surface. Therefore, the presence of more OTA was expected to lead to the release of more OTA aptamer, which meant less OTA aptamer remained on electrode for producing LAMP amplicons, resulting in less Ru(phen)32+ interlaced into the formed amplicons within a fixed Ru(phen)32+ amount with an obviously increased ECL signal input. As a result, a detection limit as low as 10 fM for OTA was achieved. The aptasensor also has good reproducibility and stability.

In this work, a novel pseudo triple-enzyme cascade catalysis amplification strategy was employed to fabricate a highly sensitive electrochemiluminescence (ECL) aptasensor for thrombin (TB) detection. The signal amplification of the proposed aptasensor was based on the synergistic catalysis of glucose dehydrogenase (GDH) and hemin/G-quadruplex to generate a co-reactant in situ for the ECL of peroxydisulfate. Gold nanorods (AuNRs) conjugated with GDH and hemin/G-quadruplex were used as the secondary aptamer bioconjugate (TBA II) in this aptasensor. TB was sandwiched between TBA II and a thiol-terminated TB aptamer which self-assembled on the AuNRs-modified electrode. The pseudo triple-enzyme cascade catalysis was completed as follows: firstly, GDH could effectively catalyze the oxidation of glucose to gluconolactone, coupling with the reduction of β-nicotinamide adenine dinucleotide hydrate (NAD+) into β-nicotinamide adenine dinucleotide hydrogen (NADH). Then, the hemin/G-quadruplex acted as NADH oxidase, could rapidly oxidize NADH into NAD+ accompanied with the generation of H2O2. Simultaneously, the hemin/G-quadruplex served as the horseradish peroxidase (HRP)-mimicking DNAzyme that further catalyzed the reduction of H2O2 to generate O2in situ. Then the O2 produced acted as the co-reactant of peroxydisulfate, resulting in significant ECL signal amplification and highly sensitive ECL detection. The proposed aptasensor showed a wide linear range of 0.0001–50 nM with a low detection limit of 33 fM (S/N = 3) for TB determination. The present work demonstrated that the novel strategy has great advantages of sensitivity, selectivity and reproducibility, which hold new promise for highly sensitive bioassays applied in clinical detection.

In this work, Pt/Au bimetallic nanoparticles (Pt/Au NPs) were used as nanocarriers to develop an electrochemiluminescence (ECL) immunosensor for sensitive cardiac troponin I (cTnI) detection, coupling with enzyme-based signal amplification. First, gold nanoparticles modified Ru(phen)32+-doped silica nanoparticles (Au@RuSiO2 NPs) with numerous luminophores were used as a platform, potentially increasing the signal intensity. Second, Pt/Au NPs with large surface area and rich surface atoms were a superior matrix for the immobilization of numerous antibodies (Ab2), poly(L-histidine) (PLH) and glucose dehydrogenase (GDH). More importantly, the PLH-protected GDH exhibited excellent enzymatic activity for the oxidation of glucose accompanied by the reduction of NAD+ to NADH. The in situ generated NADH acted as a co-reactant of Ru(phen)32+, significantly enhancing the ECL signal. In this manner, the designed immunosensor displayed high sensitivity for the detection of cTnI in the range of 0.010 ng mL−1 to 10 ng mL−1 with a detection limit of 3.3 pg mL−1 (S/N = 3). The proposed strategy holds a new promise for highly sensitive bioassays for application in clinical analyses.

In this study, a new universal biosensor based on luminol anodic electrochemiluminescence (ECL) for the detection of microRNA-155 was constructed by using hydrogen peroxide (H2O2) as a co-reactant and hemin as a catalyzer for signal amplification. The bare glassy carbon electrode (GCE) was first electrodeposited with Au nanoparticles (AuNPs). Then, helper DNA, which was partly complementary with the hairpin DNA chains, was assembled on the prepared GCE. Target microRNA-155 and the hairpin hybridization chains could create a formation of extended double-stranded DNA (dsDNA) polymers through the displacement of hybridization chains and the hybridization chain reaction (HCR). The HCR-generated dsDNA polymers give rise to the intercalation of a lot of hemin which could catalyze the oxidation of H2O2, leading to a remarkably amplified ECL signal output. The proposed biosensor showed a wide linear range from 5 fM to 50 pM with a relatively low detection limit of 1.67 fM for microRNA-155 detection. With excellent selectivity, good stability and high sensitivity, the proposed biosensor is promising in the development of a high-throughput assay of microRNA-155.

An electrochemiluminescence (ECL) immunoassay protocol was developed based on mimic-intramolecular interaction for sensitive detection of prostate specific antigen (PSA). It was constructed by integrating the ECL luminophore (tris(4,4′-dicarboxylicacid-2,2′-bipyridyl)-ruthenium(II)dichloride (Ru(dcbpy)32+)) and coreactant (histidine) into the supersandwich DNA structure. This strategy was more effective in amplifying the ECL signal by shortening the electronic transmission distance, improving the ECL luminous stability and enhancing the ECL luminous efficiency. The ECL matrices denoted as MWCNTs@PDA–AuNPs were fabricated through spontaneous oxidative polymerization of dopamine (DA) on multiwalled carbon nanotubes (MWCNTs) and reducing HAuCl4 to produce gold nanoparticles (AuNPs) by DA simultaneously. Then, the prepared matrices were applied to bind capture antibodies. Moreover, supersandwich Ab2 bioconjugate was designed using a PAMAM dendrimer to immobilize the detection antibody and supersandwich DNA structure. The PAMAM dendrimer, with a plurality of secondary and tertiary amine groups, not only facilitated high-density immobilization of the detection antibody and supersandwich DNA structure, but also greatly amplified the ECL signal of Ru(dcbpy)32+. The supersandwich DNA structure contained multiple Ru(dcbpy)32+ and histidine, further amplifying the ECL signal. The proposed supersandwich immunosensor showed high sensitivity with a detection limit of 4.2 fg mL−1 and a wide linear range of 0.01 pg mL−1–40.00 ng mL−1. With the excellent stability, satisfying precision and reproducibility, the proposed immunosensor indicates promising practicability for clinical diagnosis.

In the present work, we constructed a new label-free “inter-sandwich” electrochemical aptasensor for thrombin (TB) detection by employing a cleavage-based hybridization chain reaction (HCR). The designed single-stranded DNA (defined as binding DNA), which contained the thrombin aptamer binding sequence, a DNAzyme cleavage site and a signal reporter sequence, was first immobilized on the electrode. In the absence of a target TB, the designed DNAzymes could combine with the thrombin aptamer binding sequence via complementary base pairing, and then Cu2+ could cleave the binding DNA. In the presence of a target TB, TB could combine with the thrombin aptamer binding sequence to predominantly form an aptamer–protein complex, which blocked the DNAzyme cleavage site and prevented the binding DNA from being cleaved by Cu2+-dependent DNAzyme. As a result, the signal reporter sequence could leave the electrode surface to trigger HCR with the help of two auxiliary DNA single-strands, A1 and A2. Then, the electron mediator hexaammineruthenium (III) chloride ([Ru(NH3)6]3+) was embedded into the double-stranded DNA (dsDNA) to produce a strong electrochemical signal for the quantitative measurement of TB. For further amplification of the electrochemical signal, graphene reduced by dopamine (PDA-rGO) was introduced as a platform in this work. With this strategy, the aptasensor displayed a wide linearity in the range of 0.0001 nM to 50 nM with a low detection limit of 0.05 pM. Moreover, the resulting aptasensor exhibited good specificity and acceptable reproducibility and stability. Because of these factors, the fabrication protocol proposed in this work may be extended to clinical application.

We developed a signal-on electrochemiluminescence (ECL) aptasensor by using SI-ATRP to facilitate high-density immobilization of luminophores and manganese dioxide–graphene (MnO2–GO) composite to indirect deactivate the excited state of Ru(dcbpy)32+ for ultrasensitive detection of carcinoembryonic antigen (CEA). In this approach, manganese dioxide–graphene (MnO2–GO) composite served as an efficient quencher for indirect deactivating the excited state of Ru(dcbpy)32+. Surface initiated atom transfer radical polymerization (SI-ATRP) was applied to functionalize multiwalled carbon nanotubes (MWNTs) with glycidyl methacrylate (GMA) as the functional monomer. A nanocomposite material of polyamidoamine (PAMAM) dendrimer encapsulated AuNPs was used as the carrier to combine Ru(dcbpy)32+ and poly-GMA together for the synthesis of the ECL matrices. The prepared matrices were applied to bind amino-modified auxiliary probe I (A1), which was partially complementary with the CEA aptamer. Meanwhile, the MnO2–GO composite was modified with another amino-modified CEA aptamer-partial-complementary auxiliary probe II (A2). Through the hybridization of CEA aptamer with A1 and A2, the quencher MnO2–GO composite was linked with the ECL matrices, by which a low ECL signal was detected (off-state). However, in the presence of CEA, the sandwich-like structure was destroyed because CEA would bind to its aptamer in lieu of the auxiliary probes, which resulted in a recovery of ECL signal (on-state). The proposed ECL aptasensor showed high sensitivity with a detection limit of 25.3 fg mL−1 and a wide linear range of 0.1 pg mL−1 to 20 ng mL−1. Consequently, with the excellent sensitivity, stability and satisfying precision, the as-proposed strategy constitutes a promising detection technique for clinical diagnosis.

A simple label-free electrochemiluminescence (ECL) aptasensor was constructed for the detection of thrombin (TB). We explored the possibility of using π–π stacking to synthesis Ru(phen)32+-encapsulated CNTs nanocomposites (Ru(phen)32+@CNTs), which were immobilized on a glassy carbon electrode (GCE) surface by nafion to form the Ru(phen)32+@CNTs-Nf film as an ECL signal probe. Hollow gold nanospheres (HGNPs) were adsorbed onto the modified electrode to immobilize thrombin binding aptamer (TBA). When TB is bound by its TBA, the TB–TBA complex is electrical inertia, resulting in the decrease of ECL intensity. This work provided a new method for immobilizing the luminophore on an electrode surface and would extend the application of CNTs.

•We employed the integration of LAMP, aptamer and the electrochemical method for the sensitive detection of Ochratoxin A (OTA) for the first time.•This assay was demonstrated that the LAMP reaction can be applied to ultrasensitive detection of OTA.•The prepared aptasensor exhibited low detection limit and wide linear range to OTA.Loop-mediated isothermal amplification (LAMP) is an outstanding DNA amplification procedure, in which the reaction can accumulate 109 copies from less than 10 copies of input template within an hour. While the amplification reaction is extremely powerful, the quantitative detection of LAMP products is still analytically difficult. Besides, the type of targets that LAMP can detect is also less, which to some extent limited the application of LAMP. In this study, we are reporting for the first time an efficient and accurate detection system which employs the integration of LAMP, aptamer and the electrochemical method for the sensitive detection of Ochratoxin A (OTA). Aptamers were designed as the forward outer primer to trigger the LAMP reaction, and then the LAMP amplification products were combined with a redox active molecule methylene blue (MB) and analyzed by an electrode using differential pulse voltammograms (DPV). As the reaction progresses, the MB intercalated into double-stranded regions of LAMP amplicons reduces the free MB concentration. Hence, the peak current of reaction mixture decreased with the amplification because of the slow diffusion of MB-amplified DNA complex to the electrode surface. The peak height of the current was related to the input amount of the aptamers, providing a ready means to detection the concentration of OTA. With such design, the proposed assay showed a good linear relationship within the range of 0.001–50 nM with a detection limit of 0.3 pM (defined as S/N=3) for OTA.

•The self-enhanced Ru(II)@l-Cys complex was used as novel ECL luminophor.•Gold nanorods were used as carriers to immobilize anti-cTnI and the luminophor.•The immnuosensor exhibits high sensitivity, good stability and satisfying selectivity.To promote the luminous efficiency of luminophore, traditional electrochemiluminescence (ECL) immunoassay usually adopts the adding of coreactant into testing solution. However, many adverse micro-environmental factors in the solution are a limiting factor in ECL analytical techniques and received extensive attention. In our work, a self-enhanced ECL luminophore was synthesized by combining the coreactant (l-cysteine) and the luminophor (tris (4,4′-dicarboxylicacid-2,2′-bipyridyl) ruthenium(II) dichloride (Ru(dcbpy)32+)) to form one Ru(II) complex and was applied to fabricate a reagentless immunosensor for the detection of cardiac troponin I (cTnI) for the first time. Herein gold nanorods (AuNRs), due to their high specific surface area and good electrocatalytic ability, were used as carriers for the immobilization of Ru(II) complex and cTnI antibody to obtain the Ab2 bioconjugates as signal labels. The application of the self-enhanced Ru(II) complex not only avoided the addition of any coreactant into testing solution for simplifying the operation, but also achieved the intramolecular reaction for improving the ECL signal due to shorter electron transfer path and less energy loss. In view of these advantages, the proposed immunosensor achieved a wide linear range from 0.25 pg/mL to 0.1 ng/mL with an impressive detection limit of 0.083 pg/mL for cTnI (S/N=3).

•Aushell@GOD nanospheres were synthesized by the template of GOD crosslinked with GA.•Electrogenerated chemiluminescence glucose sensor was designed based on Aushell@GOD.•Aushell@GOD can increase the loading of GOD and keep its biological activity.•GOD molecules existed inside and outside of Aushell, which could amplify the ECL signal.Well-distributed hollow gold nanospheres (Aushell@GOD) (20±5 nm) were synthesized using the glucose oxidase (GOD) cross-linked with glutaraldehyde as a template. A glucose biosensor was prepared based on Aushell@GOD nanospheres for catalyzing luminol electrogenerated chemiluminescence (ECL). Firstly, chitosan was modified in a glassy carbon electrode which offered an interface of abundant amino-groups to assemble Aushell@GOD nanospheres. Then, glucose oxidase was adsorbed on the surface of Aushell@GOD nanospheres via binding interactions between Aushell and amino groups of GOD to construct a glucose biosensor. The Aushell@GOD nanospheres were investigated with TEM and UV–vis. The ECL behaviors of the biosensor were also investigated. Results showed that, the obtained Aushell@GOD nanospheres exhibited excellent catalytic effect towards the ECL of luminol-H2O2 system. The response of the prepared biosensor to glucose was linear with the glucose concentration in the range of 1.0 μM to 4.3 mM (R=0.9923) with a detection limit of 0.3 μM (signal to noise=3). This ECL biosensor exhibited short response time and excellent stability for glucose. At the same time the prepared ECL biosensor showed good reproducibility, sensitivity and selectivity.GraphicalHollow gold nanospheres (Aushell@GOD) have been synthesized with the method of using GOD cross-linked glutaraldehyde as template. A glucose biosensor was prepared based on the Aushell@GOD nanoparticles and electrogenerated chemiluminescence (ECL) technology. Results showed that, the obtained Aushell@GOD nanoparticles exhibited excellent catalytic effect towards the ECL of luminol-H2O2 system.

•Hemin-GNs could further enhance the luminol ECL in the presence of H2O2.•Glucose oxidase was used to label the Ag-rGO–Ab2 for generating H2O2 in situ.•With the catalysis of AgNPs, amplified ECL signal could be obtained.•The immnuosensor exhibits high sensitivity, good stability and satisfying selectivity.A novel and ultrasensitive electrochemiluminescence (ECL) immunosensor, which was based on the amplifying ECL of luminol by hemin-reduced graphene oxide (hemin-rGO) and Ag nanoparticles (AgNPs) decorated reduced graphene oxide (Ag-rGO), was constructed for the detection of carcinoembryonic antigen (CEA). For this proposed sandwich-type ECL immunosensor, Au nanoparticles electrodeposited (DpAu) onto hemin-rGO (DpAu/hemin-rGO) constructed the base of the immunosensor. DpAu had outstanding electrical conductivity to promote the electron transfer at the electrode interface and had good biocompatibility to load large amounts of primary antibody (Ab1), which provided an excellent platform for this immunosensor. Moreover, AgNPs and glucose oxidase (GOD) functionalized graphene labeled secondary antibody (Ag-rGO–Ab2–GOD) was designed as the signal probe for the sandwiched immunosensor. Not only did the hemin-rGO improve the electron transfer of the electrode surface, but hemin also further amplified the ECL signal of luminol in the presence of hydrogen peroxide (H2O2). With the aid of Ag-rGO–Ab2–GOD, enhanced signal was obtained by in situ generation of H2O2 and catalysis of AgNPs to ECL reaction of the luminol–H2O2 system. The as-prepared ECL immunosensor exhibited excellent analytical property for the detection of CEA in the range from 0.1 pg mL−1 to 160 ng mL−1 with a detection limit of 0.03 pg mL−1 (SN−1=3).

•The magnetic nanomaterial GO-Fe3O4-DTDP acts as integrate ionophore-transducer.•A covalent mode was adopted to avoid the leaching out of Fe3O4 nanoparticles.•GO-Fe3O4 hybrids improved the sensitivity of lanthanum (III) ion selective electrode.•The prepared electrode showed low detection limit and excellent Nernstian response.For the first time, the analytical application of integrate ionophore-transducer material based on magnetic graphene hybrids and 2,2-dithiodipyridine (DTDP) in solid-contact lanthanum (III) selective electrode is reported. The attachment of Fe3O4 nanoparticles (NPs) to graphene oxide (GO) for magnetic graphene hybrid is achieved by covalent bonding, and the universal problem, Fe3O4 NPs may easily leach out from the graphene during application, is successfully solved by the method above. The proposed electrode exhibits an excellent near-Nernstian response to lanthanum (III) ranging from 1.0 × 10−9 to 1.0 × 10−3 M with a slope of 17.81 mV/dec. Moreover, the excellent performance on fairly good selectivity, wide applicable pH range (3.0_8.0), fast response time (10 s) and long life time (2 months) reveal the superiority of the electrode. Most importantly, we have made a great improvement in the detection limit (2.75 × 10−10 M), which brings new dawn to the real-time detection of lanthanum (III) using ion selective electrode.

•Chi-GR-CNTs composite exhibited strong cathodic ECL behavior of luminol under −0.1 to 0.4 V.•The nano-AuPt was adopted to further enhance ECL signal and mobilize more proteins.•Glucose oxidase was used to block non-specific sites for generating H2O2 in situ.•The prepared immunosensor displayed an excellent sensitivity.In the present study, a novel and ultrasensitive electrochemiluminescence (ECL) immunosensor based on luminol cathodic ECL was fabricated by using Au nanoparticles and Pt nanoparticles (nano-AuPt) electrodeposited on graphene–carbon nanotubes nanocomposite as platform for the detection of carcinoembryonic antigen (CEA). For this introduced immunosensor, graphene (GR) and single wall carbon nanotubes (CNTs) dispersed in chitosan (Chi-GR-CNTs) were firstly decorated on the bare gold electrode (GE) surface. Then nano-AuPt were electrodeposited (DpAu-Pt) on the Chi-GR-CNTs modified electrode. Subsequently, glucose oxidase (GOD) was employed to block the non-specific sites of electrode surface. When glucose was present in the working buffer solution, GOD immediately catalyzed the oxidation of glucose to in situ generate hydrogen peroxide (H2O2), which could subsequently promote the oxidation of luminol with an amplified cathodic ECL signal. The proposed immunosensor was performed at low potential (−0.1 to 0.4 V) and low concentration of luminol. The CEA was determined in the range of 0.1 pg mL−1 to 40 ng mL−1 with a limit of detection down to 0.03 pg mL−1 (S N−1 = 3). Moreover, with excellent sensitivity, selectivity, stability and simplicity, the as-proposed luminol-based ECL immunosensor provided great potential in clinical applications.

In this work, we demonstrated a novel sensitive sandwich-type pseudobienzyme aptasensor for thrombin detection. Greatly amplified sensitivity was based on mesoporous silica-multiwalled carbon nanotube (mSiO2@MWCNT) nanocomposites as enhanced materials and a pseudobienzyme electrocatalytic system. Firstly, the mSiO2@MWCNT nanocomposites not only have good biocompatibility and a suitable microenvironment for stabilizing the aptamer assembly, but also can load large amounts of electron mediator thionine (Thi), platinum nanoparticles (PtNPs) and hemin/G-quadruplex bioelectrocatalytic complex. Moreover, in the presence of H2O2 in an electrolytic cell, the synergistic reaction of PtNPs and hemin/G-quadruplex bioelectrocatalyzed the reduction of H2O2, dramatically amplifying the response signals of electron mediator Thi and improving the sensitivity. Secondly, dendrimer functionalized reduced graphene oxide (PAMAM–rGO) as the biosensor platform enhanced the surface area for the immobilization of abundant primary aptamers as well as facilitated electron transfer from Thi to the electrode, thus amplifying the detection response. Using the above multiple effects, the approach showed a high sensitivity and a wider linearity for the detection of thrombin in the range between 0.0001 nM and 80 nM with a detection limit of 50 fM. This new design avoided the fussy labeling process and the spatial distribution of each sequentially acting enzyme, which provided an ideal candidate for the development of a sensitive and simple bioanalytical platform.

In this report, gold nanoparticle–graphene nanohybrids (Au–GR) and 3-amino-5-mercapto-1,2,4-triazole-functionalized multiwall carbon nanotubes (MWCNT–SH) were synthesized. And a novel hybrid material MWCNT–SH@Au–GR was obtained by the interaction between gold nanoparticles of two dimensional (2D) Au–GR and SH groups of 1D MWCNT–SH. Due to the synergistic effects between MWCNT–SH and Au–GR and excellent film forming ability of MWCNT–SH@Au–GR, the obtained MWCNT–SH@Au–GR was used as a modifier to fabricate a chemically modified electrode for the simultaneous determination of hydroquinone (HQ), catechol (CC), resorcinol (RC) and nitrite (NO2−). Scanning electron microscopy (SEM) was employed to characterize the morphology of MWCNT–SH@Au–GR. The electrochemical behavior of the sensor was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Results showed that it was feasible to simultaneously measure HQ, CC, RC and NO2−. The linear response ranges for HQ, CC, RC and NO2− were 54.5–1250.5 μM, 11.0–126.0 μM, 43.5–778.5 μM and 86.0–7500.0 μM and the detection limits (S/N = 3) were 4.17 μM, 1.00 μM, 7.80 μM and 23.5 μM, respectively.

•An ECL immunosensor based on HCR and glucose oxidase catalysis was constructed.•The HCR was developed for improving the immobilization of glucose oxidase.•Glucose oxidase was used to in situ generate H2O2 as luminol's co-reactant.In this work, we described a simple and highly sensitive electrochemiluminescence (ECL) strategy for IgG detection. Firstly, l-cysteine functionalized reduced graphene oxide composite (l-cys-rGO) was decorated on the glassy carbon electrode (GCE) surface. Then anti-IgG was immobilized on the modified electrode surface through the interaction between the carboxylic groups of the l-cys-rGO and the amine groups in anti-IgG. And then biotinylated anti-IgG (bio-anti-IgG) was assembled onto the electrode surface based on the sandwich-type immunoreactions. By the conjunction of biotin and streptavidin (SA), SA was immobilized, which in turn, combined with the biotin labeled initiator strand (S1). In the presence of two single DNA strands of glucose oxidase labeled S2 (GOD-S2) and complementary strand (S3), S1 could trigger the hybridization chain reaction (HCR) among S1, GOD-S2 and S3. Herein, due to HCR, numerous GOD was efficiently immobilizated on the sensing surface and exhibited excellent catalysis towards glucose to in situ generate amounts of hydrogen peroxide (H2O2), which acted as luminol's co-reactant to significantly enhance the ECL signal. The proposed ECL immunosensor presented predominate stability and high sensibility for determination of IgG in the range from 0.1 pg mL−1 to 100 ng mL−1 with a detection limit of 33 fg mL−1 (S/N=3). Additionally, the designed ECL immunosensor exhibited a promising application for other protein detection.

This work described a two-step conjugate synthesis of a porous nanostructured materials (PTCA–Cys) composed of 3,4,9,10-perylenetetracarboxylic acid (PTCA) and l-cysteine (Cys) and then the sensor prepared by the deposited gold nanocrystals (DpAu) immobilized in this nanostructure film was developed. The interesting PTCA–Cys layer not only could provide SH-functionalized interface but also easily forms a stable thin film on the electrode surface with the porous nanostructure, thus, it is very beneficial to electrode modification. Furthermore, with the DpAu film onto PTCA–Cys modified electrode, the proposed sensors exhibited the excellent catalytic activity and the high selectivity toward the oxidation of AA, DA and UA. Moreover, scanning electron microscopy, cyclic voltammetry and different pulse voltammetry were employed to characterize the sensors. Under the optimal conditions, the linear response range for simultaneous detection of AA, DA, and UA were 20–700 μM, 2–402 μM and 0.4–252.4 μM, respectively, and the detection limits were 6.40 μM, 0.67 μM and 0.12 μM (S/N = 3). More importance, the proposed method offers promise for simple, rapid and cost-effective analysis of small biomolecules.

•Immunosensor for simultaneous detection of four biomarkers on identical interface.•Aq, Thi, Fc and Co(bpy)33+ were adopted as signal tags.•Preparing Au/PDDA/PTCA/CNTs/redox-probe@D-Ab as signal tracer.•The immunosensor exhibited excellent sensitivity and selectivity.In this paper, a simple and sensitive amperometric immunosensor for simultaneous detection of four biomarkers by using distinguishable redox-probes as signal tags was proposed for the first time. In sandwich immunoassay format, four kinds of capture antibodies (C-Ab) were immobilized by gold nanoparticles (AuNPs) electro-deposited on the surface of glass carbon electrode (GCE); four kinds of detection antibodies (D-Ab) labeled with different redox probes (including anthraquinone 2-carboxylic acid (Aq), thionine (Thi), ferrocenecarboxylic acid (Fc) and tris(2,2’-bipyridine-4,4’-dicarboxylic acid) cobalt(III) (Co(bpy)33+)), were combined with 3,4,9,10-perylenetetracarboxylic acid (PTCA), poly(diallyldimethylammonium chloride) (PDDA) and AuNPs functionalized carbon nanotubes, and served as signal tracer. When four target antigens were present, differential pulse voltammetry (DPV) scan exhibited four well-resolved peaks, each peak indicated one antigen, and its intensity was quantitative correlational to the concentration of corresponding analyte. To verify the strategy, four biomarkers for diagnosis of colorectal carcinoma, including carcinoembryonic antigen (CEA), carbohydrate antigen (CA) 19-9 CA125, and CA242, were used as model analytes, the immunosensor exhibited high selectivity and sensitivity, and peak current displayed good linear relationship to logarithm concentration in the ranges from 0.016 to 15 ng mL−1 for CEA; 0.008 to 10 ng mL−1 for CA19-9; 0.012 to 12 ng mL−1 for CA125; 0.010 to 10 ng mL−1 for CA242, and low detection limits of 4.2, 2.8, 3.3 and 3.8 pg mL−1, respectively.In this work, an amperometric immunosensor for simultaneous detection of four biomarkers by using distinguishable redox-probes as signal labels was proposed for the first time. Four kinds of redox probes including anthraquinone 2-carboxylic acid (Aq), thionine (Thi), ferrocenecarboxylic acid (Fc) and tris(2,2(-bipyridine-4,4(-dicarboxylic acid) cobalt(III) (Co(bpy)33+ were adopted to label four detection antibodies (D-Ab) through amide reaction, then integrated with functionalized carbon nanotubes (CNTs), and served as tracer in sandwich-typed immunoassay format. Differential pulse voltammetry (DPV) scan exhibited four well-resolved peaks at different potential position, each peak indicated one target antigen, and the current intensity was quantitative to the concentration of corresponding analyte illustrates the fabricated procedure and the principle of sandwich-type immunoassay.

•An ECL immunosensor was constructed based on an amplified cathodic ECL of luminol.•AuNPs deposited on CNTs–Gra improved biocompatible surface area and electron transfer rate.•Pd&PtNPs@rGO enhanced the loading amount of GOD and amplified the cathodic ECL of luminol.•The proposed immunosensor had excellent performance for the detection of CEA.An ultrasensitive electrochemiluminescence (ECL) immunosensor was constructed for ultrasensitive detection of carcinoembryonic antigen (CEA) based on an amplified cathodic ECL of luminol at low potential. Firstly, Au nanoparticles (AuNPs) were electrodeposited onto single walled carbon nanotube–graphene composites (CNTs–Gra) coated glass carbon electrode (GCE) with enhanced surface area and good biocompatibility to capture primary antibody (Ab1) and then bind the antigen analytes. Secondly, Pd and Pt nanoparticles (Pd&PtNPs) decorated reduced graphene oxide (Pd&PtNPs@rGO) and glucose oxidase (GOD) labeled secondary antibody (Pd&PtNPs@ rGO–GOD–Ab2) could be captured onto the electrode surface by a sandwich immunoassay protocol to generate amplified cathodic ECL signals of luminol in the presence of glucose. The Pd&PtNPs@rGO composites and loaded GOD promoted luminol cathodic ECL response by efficiently catalyzing glucose to in-situ produce amount of hydrogen peroxide (H2O2) working as a coreactant of luminol. Then in turn Pd&PtNPs catalyzed H2O2 to generate various reactive oxygen species (ROSs), which accelerated the cathodic ECL reaction of luminol, enhanced the cathodic ECL intensity of luminol and improved the sensitivity of the immunosensor. The as-proposed ECL immunosensor exhibited sensitive response on the detection of CEA ranging from 0.0001 ng mL−1 to 160 ng mL−1 with a detection limit of 0.03 pg mL−1 (S/N=3). Moreover, the stability, specificity, lifetime and reproducibility tests demonstrated the feasibility of the developed immunoassay, which can be further extended to the detection of other disease biomarkers.

A novel immunoassay protocol for simultaneous electrochemical determination of alpha-fetoprotein (AFP), carcinoembryonic (CEA) and streptococcus suis serotype 2 (SS2) was designed. As standard sandwich-type immunoassay format, three primary antibodies (Ab1), anti-CEA and anti-AFP and anti-SS2, were immobilized via protein A (PA) adsorbed by Nafion modified electrodes, and functionalized graphene sheets (GS), containing abundant gold nanoparticles (AuNPs) and carboxyl group, were used to immobilize secondary antibody@redox-probe so as to act as tracer. Concentration of each analyte was quantitatively related to the reduction peak current of corresponding redox-probe in differential pulse voltammetry (DPV) scan. The resulting immunosensor exhibited high selectivity and sensitivity in simultaneous determination of three analytes. The linear range was from 0.016 to 50 ng/mL for AFP with a detection limit of 5.4 pg/mL, 0.010 to 50 ng/mL for CEA with a detection limit of 2.8 pg/mL and 0.012 to 50 ng/mL for SS2 with a detection limit of 4.2 pg/mL (S/N=3).Highlights► Immunosensor for simultaneous determination of three antigens on identical interface. ► Using PA/Nafion to immobilize primary antibodies. ► Preparing PTCA/Au/GS/redox-probe@Ab2 as tracer. ► The immunosensor exhibited excellent sensitivity and selectivity.

In the present work, a tube-like structure of graphene hybrid as modifier to fabricate electrode for simultaneous detection of ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp) was reported. The hybrid was synthesized by a simple method based on graphene sheets (GS) and 3,4,9,10-perylenetetracarboxylic acid (PTCA) via π–π stacking interaction under ultrasonic condition. The combination of GS and PTCA could effectively improve the dispersion of GS, owing to PTCA with the carboxylic-functionalized interface. Comparing with pure GS or PTCA modified electrode, GS–PTCA displayed high catalytic activity and selectivity toward the oxidation of AA, DA, UA, and Trp. Moreover, cyclic voltammetry, different pulse voltammetry and scanning electron microscopy were employed to characterize the sensors. The experiment results showed that the linear response range for simultaneous detection of AA, DA, UA, and Trp were 20–420 μM, 0.40–374 μM, 4–544 μM and 0.40–138 μM, respectively, and the detection limits were 5.60 μM, 0.13 μM, 0.92 μM and 0.06 μM (S/N = 3). Importantly, the proposed method offers promise for simple, rapid, selective and cost-effective analysis of small biomolecules.Graphical abstractA tube-like structure of graphene hybrid (GS–PTCA) was synthesized via π–π stacking interaction, and was used as modifier to fabricate electrode for simultaneous detection of ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp). SEM images of GS, PTCA and GS–PTCA were presented. Under the synergistic effects between GS and PTCA, the modified electrode displayed high catalytic activity and selectivity toward the oxidation of AA, DA, UA, and Trp.Highlights► A simple strategy for simultaneous detection of AA, DA, UA and Trp has been constructed. ► The tube-like structure of graphene hybrid (GS–PTCA) was synthesized. ► The GS–PTCA provided a selective interface for discrimination of AA, DA, UA and Trp.

For the first time, a novel copper ion(II) carbon paste electrode (CPE) based on high-density carboxyl functionalized graphene oxide (GO) is reported. A new hybrid material, 2-amino-5-mercapto-1,3,4-thiiodiazole grafted onto nanoscale graphene oxide (AMT-g-NGO), was introduced as a neutral carrier. The electrode exhibits an excellent Nernstian response to copper ion(II) ranging from 1.0 × 10−7 M to 1.0 × 10−1 M with a slope of 26.2 mV dec−1. Meanwhile, the proposed electrode shows fairly good selectivity and a long life time (2 months). Moreover, the excellent performance on low detection limit (4.0 × 10−8 M), wide applicable pH range (3.0–7.0) and fast response time (15 s), reveal the superiority of the electrode. The response mechanism of the electrode was investigated using AC impedance technique and UV-vis spectroscopy. The sensor can be used as indicator electrode for potentiometric titration of Cu2+ ion with EDTA and successfully applied to the determination of Cu2+ ion in different real samples.

A new hybrid material (B15C5-MWCNTs) has been used as a neutral carrier in a carbon paste electrode for the detection of silver. B15C5-MWCNTs were synthesized by grafting 4′-aminobenzo-15-crown-5 (B15C5) onto acid-functionalized multi-walled carbon nanotubes (MWCNT-COOH) through a short 2-carbon chain spacer. The silver carbon paste electrode can be prepared by simple mixing of B15C5-MWCNTs, graphite powder and paraffin oil. B15C5-MWCNTs were not only ion-to-electron transducers but also reactive materials. With 8.4 wt% B15C5-MWCNTs proportions, the electrodes exhibited a linear response ranging from 2.7 × 10−7 to 1.0 × 10−1 M with a near Nernstian slope of 58.5 mV dec−1. The proposed electrode displayed rapid response (∼15 s) and long-time stability. Moreover, the potentiometric responses could be carried out with a wide pH range of 3.0–9.0. Then, the response mechanism of the proposed electrode was investigated by using AC impedance. Finally, the developed electrode was successfully applied in the determination of silver ions in radiology films and chloride ions in water samples.

For the first time a novel carbon paste electrode (CPE) for the detection of trace silver(I) was designed by using derivatized silica-coated multi-walled carbon nanotubes (MWCNTs@SiO2) nanocomposites as a neutral carrier. This proposed electrode, with optimum composition, exhibits a wide dynamic range of 8.6 × 10− 8 to 1.0 × 10− 1 M toward silver(I) with a detection limit of 8.0 × 10− 8 M and a Nernstian slope of 60.8 ± 0.2 mV dec− 1. Meanwhile, it also shows a good selectivity and a relatively fast response time (~ 20 s), a long lifetime (1 month) and a wide pH range (4.0–9.0). Finally, the developed CPEs were successfully applied in the potentiometric titration of potassium bromide and determination of Cl− ions in different water samples.Highlights► Derivatized MWCNTs@SiO2 nanocomposites were applied in ion-selective electrode. ► The nanocomposites exhibited a good Nernstian response to silver(I) ion. ► We studied the possible mechanism of this sensor. ► The developed CPEs were successfully applied in the determination of Cl− ions.

For the first time, triazene compound functionalized silica gel was incorporated into carbon paste electrode for the potentiometric detection of silver (I) ion. A novel diazo-thiophenol-functionalized silica gel (DTPSG) was synthesized, and the presence of DTPSG acted as not only a paste binder, but also a reactive material. The electrode with optimum composition, exhibited an excellent Nernstian response to Ag+ ion ranging from 1.0 × 10− 6 to 1.0 × 10− 1 M with a detection limit of 9.5 × 10− 7 M and a slope of 60.4 ± 0.2 mV dec− 1 over a wide pH range (4.0–9.0) with a fast response time (50 s) at 25 °C. The electrode also showed a long-time stability, high selectivity and reproducibility. The response mechanism of the proposed electrode was investigated by using AC impedance. Moreover, the electrode was successfully applied for the determination of silver ions in radiology films, and for potentiometric titration of the mixture solution of Cl− and Br− ions.Highlights► Functionalized silica gels have become promising materials. ► This work is the first attempt to apply triazene functionalized silica gel. ► The Functionalized silica gels were used to detect silver. ► The response of the previously reported papers are compared with this work. ► The result indicates the proposed electrode is better than reported Ag+ electrodes.

We reported on the synthesis and application of ionophore–gold nanoparticle conjugates in Ag+ graphene paste electrode. Ionophore was a novel graphene oxide nanosheets (NGO) covalently grafted 2-thiophenecarboxylic (TPC) hybrid material. The hybrid material NGO–TPC decorated with gold nanoparticles was used as both a receptor and an ion-to-electron transducer to fabricate Ag+ graphene paste electrode. The developed electrode was highly selective to Ag+ over other tested cations and exhibited an excellent Nernstian slope of 59.3 mV dec−1 ranging from 8.4×10−7 to 1.0×10− M with a detection limit of 6.3×10−7 M. Moreover, it also showed a fast response time and a long lifetime. Importantly, the new method of immobilizing ligands on NGO nanosheets to construct electrode successfully solved the universal problem of the electrode components loss from ion-selective electrode.Highlights► A novel graphene hybrid material was synthesized. ► Material decorated with gold nanoparticles was used for constructing Ag+ sensor. ► Sensor showed high sensitivity and selectivity to Ag+. ► Immobilizing ligands on graphene overcame the ligands loss from the electrode.

For the first time a novel derivatized multi-walled carbon nanotubes-based Pb2+ carbon paste electrode is reported. The electrode with optimum composition, exhibits an excellent Nernstian response to Pb2+ ion ranging from 5.9 × 10−10 to 1.0 × 10−2 M with a detection limit of 3.2 × 10−10 M and a slope of 29.5 ± 0.3 mV dec−1 over a wide pH range (2.5–6.5) with a fast response time (25 s) at 25 °C. Moreover, it also shows a high selectivity and a long life time (more than 3 months). Importantly, the response mechanism of the proposed electrode was investigated using AC impedance technique. Finally, the electrode was successfully applied for the determination of Pb2+ ion concentration in environmental samples, e.g. soils, waste waters, lead accumulator waste and black tea, and for potentiometric titration of sulfate anion.

A new ion-selective electrode (ISE) for the detection of trace chromium(III) was designed by using 2-acetylpyridine and nanoporous silica gel (APNSG)-functionalized carbon paste electrode (CPE). The presence of APNSG acted as not only a paste binder, but also a reactive material. With 7.5 wt% APNSG proportions, the developed electrode exhibited wide dynamic range of 1.0 × 10−8 to 1.0 × 10−3 M toward Cr(III) with a detection limit of 8.0 × 10−9 M and a Nernstian slope of 19.8 ± 0.2 mV decade−1. The as-prepared electrode displayed rapid response (∼55 s), long-time stability, and high sensitivity. Moreover, the potentiometric responses could be carried out with wide pH range of 1.5–5.0. In addition, the content of Cr(III) in food samples, e.g. coffee and tea leaves, has been assayed by the developed electrode, atomic absorption spectrophotometer (AAS) and atomic emission spectrometer (ICP-AES), respectively, and consistent results were obtained. Importantly, the response mechanism of the proposed electrode was investigated by using AC impedance and UV–vis spectroscopy.

Two new copper(II) complexes of [Cu(Ofloxacin)(phen)(H2O)] · (NO3) · 2H2O and [Cu(Levofloxacin)(phen)(H2O)] · (NO3) · 2H2O were obtained and their structures were studies. Both ligands and complexes were assayed against gram-positive and gram-negative bacteria by the in vitro doubling dilutions method. The inhibitory effect of the ligands and complexes on the leukemia HL-60 cell line were measured with the MTT assay method and the liver cancer HePG-2 cell line measured by the SRB method. The results indicated that the complexes have stronger inhibitory effect on HL-60 than on HePG-2. The complex [Cu(Levofloxacin)(phen)(H2O)] · (NO3) · 2H2O (I) has stronger effect on HL-60 than the complex (Cu(Ofloxacin)(phen)(H2O)] · (NO3) · 2H2O (II).

For the first time, a novel copper ion(II) carbon paste electrode (CPE) based on high-density carboxyl functionalized graphene oxide (GO) is reported. A new hybrid material, 2-amino-5-mercapto-1,3,4-thiiodiazole grafted onto nanoscale graphene oxide (AMT-g-NGO), was introduced as a neutral carrier. The electrode exhibits an excellent Nernstian response to copper ion(II) ranging from 1.0 × 10−7 M to 1.0 × 10−1 M with a slope of 26.2 mV dec−1. Meanwhile, the proposed electrode shows fairly good selectivity and a long life time (2 months). Moreover, the excellent performance on low detection limit (4.0 × 10−8 M), wide applicable pH range (3.0–7.0) and fast response time (15 s), reveal the superiority of the electrode. The response mechanism of the electrode was investigated using AC impedance technique and UV-vis spectroscopy. The sensor can be used as indicator electrode for potentiometric titration of Cu2+ ion with EDTA and successfully applied to the determination of Cu2+ ion in different real samples.

A new hybrid material (B15C5-MWCNTs) has been used as a neutral carrier in a carbon paste electrode for the detection of silver. B15C5-MWCNTs were synthesized by grafting 4′-aminobenzo-15-crown-5 (B15C5) onto acid-functionalized multi-walled carbon nanotubes (MWCNT-COOH) through a short 2-carbon chain spacer. The silver carbon paste electrode can be prepared by simple mixing of B15C5-MWCNTs, graphite powder and paraffin oil. B15C5-MWCNTs were not only ion-to-electron transducers but also reactive materials. With 8.4 wt% B15C5-MWCNTs proportions, the electrodes exhibited a linear response ranging from 2.7 × 10−7 to 1.0 × 10−1 M with a near Nernstian slope of 58.5 mV dec−1. The proposed electrode displayed rapid response (∼15 s) and long-time stability. Moreover, the potentiometric responses could be carried out with a wide pH range of 3.0–9.0. Then, the response mechanism of the proposed electrode was investigated by using AC impedance. Finally, the developed electrode was successfully applied in the determination of silver ions in radiology films and chloride ions in water samples.

Here, a novel sensitive electrochemiluminescence (ECL) biosensor using N doped carbon dots (N-CDs) in situ electro-polymerized onto a glassy carbon electrode (GCE) as luminophores, and Pd–Au hexoctahedrons (Pd@Au HOHs) as enhancers, was developed for the detection of intracellular lead ions (Pb2+).

A novel redox probe 3,4,9,10-perylenetetracarboxylic acid/o-phenylenediamine (PTCA/OPD) with well-defined redox peaks caused by the synergistic action between them was demonstrated via theoretical and practical research, and applied in an electrochemical aptasensor to detect thrombin (TB) based on an Fe3O4 magnetic bead (MB) as a nonenzymatic catalyst.

A multi-functional luminol-reduced Pt@Au hybrid flower-like nanocomposite (luminol–Pt@AuNF) which not only acts as an efficient signal probe but also constitutes a pseudobienzyme amplifying system with choline oxidase (ChOx) was firstly synthesized and applied to the construction of a solid-state luminol electrochemiluminescence (ECL) immunosensor for cardiac troponin I (cTnI) detection.

Here we show an amplification-coupled detection method for directly measuring released hydrogen ions during the loop mediated isothermal amplification (LAMP) procedure by using a pH meter. The genomic DNA of Nosema bombycis (N. bombycis) was amplified and detected by employing this LAMP-pH meter platform for the first time.

An ultrasensitive fluorescence assay for intracellular Pb2+ determination was proposed through target–intermediate recycling amplification based on metal-assisted DNAzyme catalysis and strand displacement reactions. Compared with only target recycling-based fluorescence assay with an M amplification ratio, the proposed assay could achieve an M × N amplification ratio to obtain an improved sensitivity by more than 10 times, in which M and N are the amplification ratios of target recycling and intermediate recycling, respectively. Remarkably, this proposed ultrasensitive fluorescence assay could be applied to the determination of various analytes with the well-designed detection probe, especially in intracellular assay, providing a promising tool for clinical diagnosis and biomedical detection.

In this work, a series of novel multifunctionalized peryleneteracarboxylic supramolecules were synthesized based on hydrogen bonding interactions between 3,4,9,10-perylenetetracarboxylic acid (PTCA) and amines, which possess large specific surface area, good membrane-forming properties and high stability. Importantly, an interesting phenomenon was found in that these series of supramolecules could conciliate disorderly redox peaks of PTCA and result in a pair of well-defined redox peaks, which were able to act as redox carriers for charge-generation and electron-transportion. And the probable mechanism for this phenomenon was discussed for the first time in detail through the integration of theoretical with practical research. To further reveal the advantages of these novel multifunctionalized supramolecule nanomaterials, PTCA/triethylamine (PTCA/TEA) was chosen as the best candidate for a redox carrier to participate in a “signal-on” aptasensor for thrombin (TB) detection by employing Fe3O4 magnetic beads (MBs) as a good enzyme mimic to catalyze the PTCA/TEA for signal amplification. As a result, a wide linear detection range of 0.0001–50 nM is acquired with a relatively low detection limit of 0.05 pM. And the proposed aptasensor exhibited good specificity and acceptable reproducibility and stability. After all, the explorations between PTCA and amines would set up a meaningful basis in seeking multifunctionalized supramolecule nanomaterials based on PTCA for extending the application of PTCA in a wider range of fields, and exploring the essential reason for the referred peculiar phenomenon for PTCA.

In this work, an ultrasensitive “on–off–on” photoelectrochemical (PEC) aptasensor was proposed based on the signal amplification of a fullerene/CdTe quantum dot (nano-C60/CdTe QDs) sensitized structure and efficient signal quenching of nano-C60/CdTe QDs by a manganese porphyrin (MnPP).

In this work, an electrochemical peptide biosensor was developed for matrix metalloproteinase-2 (MMP-2) detection by conversion of a peptide cleavage event into DNA detection with exonuclease III (Exo III)-assisted cycling signal amplification.

In this report, gold nanoparticle–graphene nanohybrids (Au–GR) and 3-amino-5-mercapto-1,2,4-triazole-functionalized multiwall carbon nanotubes (MWCNT–SH) were synthesized. And a novel hybrid material MWCNT–SH@Au–GR was obtained by the interaction between gold nanoparticles of two dimensional (2D) Au–GR and SH groups of 1D MWCNT–SH. Due to the synergistic effects between MWCNT–SH and Au–GR and excellent film forming ability of MWCNT–SH@Au–GR, the obtained MWCNT–SH@Au–GR was used as a modifier to fabricate a chemically modified electrode for the simultaneous determination of hydroquinone (HQ), catechol (CC), resorcinol (RC) and nitrite (NO2−). Scanning electron microscopy (SEM) was employed to characterize the morphology of MWCNT–SH@Au–GR. The electrochemical behavior of the sensor was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Results showed that it was feasible to simultaneously measure HQ, CC, RC and NO2−. The linear response ranges for HQ, CC, RC and NO2− were 54.5–1250.5 μM, 11.0–126.0 μM, 43.5–778.5 μM and 86.0–7500.0 μM and the detection limits (S/N = 3) were 4.17 μM, 1.00 μM, 7.80 μM and 23.5 μM, respectively.