Metal nanoclusters (NCs) as a new type of electrochemiluminescence (ECL) nanomaterials have attracted great attention, but their applications are limited due to relatively low luminescent efficiency and a complex preparation process. Herein, an ultrasensitive ECL biosensor for the detection of Cyclin-D1 (CCND1) was designed by utilizing in situ electrogenerated silver nanoclusters (AgNCs) as ECL emitters and Fe3O4–CeO2 nanocomposites as a coreaction accelerator. The ECL luminous efficiency of AgNCs on the electrode could be significantly enhanced with the use of the Fe3O4–CeO2 for accelerating the reduction of S2O82– to generate the strong oxidizing intermediate radical SO4•–. As a result, the assay for CCND1 detection achieved excellent sensitivity with a linear range from 50 fg/mL to 50 ng/mL and limit of detection down to 28 fg/mL. Impressively, the efficiency of Traditional Chinese Medicines (TCM), sophorae, toward MCF-7 cells was successfully investigated due to the overexpression of CCND1 in relation to the growth and metastasis of MCF-7 human breast cancer cells. In general, the proposed strategy provided an effective method for anticancer drug screening and expanded the application of metal NCs in ultrasensitive biodetection.

•A Pb2+ biosensor with high specificity was constructed by using specific DNAzymes.•A Pt@PdNCs and MnTMPyP cooperatively amplified electrochemical response signal.•The signal was amplified by dendritic structure DNA and catalytic hairpin assembly.In this work, a sensitive electrochemical biosensing to Pb2+ was proposed based on the high specificity of DNAzymes to Pb2+. The response signal was efficiently amplified by the catalytic hairpin assembly induced by strand replacement reaction and the formation of dendritic structure DNA (DSDNA) by layer-by-layer assembly. Firstly, in the presence of Pb2+, the substrate strand (S1) of the Pb2+-specific DNAzymes was specifically cleaved by Pb2+. Secondly, one of the two fragments (rS1) introduced into the electrode surface was hybridized with a hairpin DNA (H1) and further replaced by another hairpin DNA (H2) by the hybridization reaction of H1 with H2. The released rS1 then induced the next hybridization with H1. After repeated cycles, the catalytic recycling assembly of H2 with H1 was completed. Thirdly, two bioconjugates of Pt@Pd nanocages (Pt@PdNCs) labeled with DNA S3/S4 and electroactive toluidine blue (Tb) (Tb-S3-Pt@PdNCs and Tb-S4-Pt@PdNCs) were captured onto the resultant electrode surface through the hybridization of S3 and H2, S3 and S4, resulting in the formation of DSDNA triggered by layer-by-layer assembly. This formed DSDNA greatly facilitated the immobilization of manganese(III) meso-tetrakis (4-N-methylpyridiniumyl)-porphyrin (MnTMPyP) as mimicking enzyme. Under the synergistic catalysis of Pt@PdNCs and MnTMPyP to H2O2 reduction, the effective signal amplification of the developed Pb2+ biosensor was achieved. As a result, the sensitive detection of the proposed electrochemical strategy for Pb2+ was greatly improved in the range of 0.1 pM–200 nM with a detection limit of 0.033 pM.

Herein, based on G-rich lead-specific aptamer (LSA) as the recognition element of target lead ion (Pb2+), a label-free and enzyme-free electrochemical aptasensor for Pb2+ was developed by using metal-organic frameworks (MIL-101(Fe)) decorated with AgPt nanoparticles (AgPtNPs) as electrochemical probes and signal enhancers. The as-prepared AgPtNPs/MIL-101(Fe) that presented both inherent redox activity from MIL-101(Fe) and excellent electrocatalytic activity was further conjugated with single-strand DNA partially complementary to LSA (CS). In the presence of Pb2+, the G-rich LSA, being incubated onto the modified electrode surface, was specifically folded to be stable G-quadruplex structure. Through the DNA hybridization reaction between LSA and CS, the unfolded G-rich LSA captured the proposed signal probes CS-immobilized AgPtNPs/MIL-101(Fe) in the electrode surface. As a result, the detectable electrochemical signal generated by MIL-101(Fe) was dependent on Pb2+ concentration. The cooperative electrocatalysis of AgPtNPs and MIL-101(Fe) effectively enhanced the response signal and greatly improved the detection sensitivity. Thus, the developed aptasensor for Pb2+ displayed a wide linear range from 0.1 pM to 100 nM with a detection limit of 0.032 pM, as well as excellent specificity, good stability, and acceptable reproducibility. This would make the proposed label-free and enzyme-free method be promising and potential candidate for sensitive and cost-effective detection of Pb2+ in real samples.

In this work, a simple and sensitive electrochemical aptasensor for protein (thrombin – TB used as the model) was developed by using cubic Cu2O nanocages (Cu2O-NCs) loaded with Au nanoparticles (AuNPs@Cu2O-NCs) as non-enzymatic electrocatalysts and robust redox probes. Through the specific sandwich-type reaction between TB and TB aptamers (TBA), the formed AuNPs@Cu2O-NCs bound with NH2-TBA were captured onto the electrode surface modified with SH-TBA. Based on the inherent redox activity of AuNPs@Cu2O-NCs with cubic nanostructures, a detectable electrochemical signal was generated which was dependent on the analyte concentration. Meanwhile, AuNPs@Cu2O-NCs showed an efficient electrocatalytic capability in the reduction of H2O2, resulting in a significant enhancement of the response signal. Thus, the simplification of the proposed strategy and the improvement of analytical performances were easily achieved with a sub-picomolar sensitivity (the limit of detection was 0.066 pmol L−1). The applicability of the simple and sensitive aptasensor was successfully demonstrated by assaying TB in human serum samples. This non-enzymatic detection platform would be potential and promising in clinical diagnostics and protein analysis techniques.

•A sensitive electrochemical impedimetric aptasensor was developed for protein assay.•Metal-organic frameworks as nanocarriers were immobilized with Pt nanoparticles.•Hemin/G-quadruplex as mimicking DNAzyme was formed by binding hemin with aptamer.•GOx-initiated cascade reactions were cooperatively driven by mimicking peroxidases.•Impedimetric response signal was efficiently amplified based on cascade catalysis.Based on cascade catalysis amplification driven by glucose oxidase (GOx), a sensitive electrochemical impedimetric aptasensor for protein (carcinoembryonic antigen, CEA as tested model) was proposed by using Cu-based metal-organic frameworks functionalized with Pt nanoparticles, aptamer, hemin and GOx (Pt@CuMOFs-hGq-GOx). CEA aptamer loaded onto Pt@CuMOFs was bound with hemin to form hemin@G-quadruplex (hGq) with mimicking peroxidase activity. Through sandwich-type reaction of target CEA and CEA aptamers (Apt1 and Apt2), the obtained Pt@CuMOFs-hGq-GOx as signal transduction probes (STPs) was captured to the modified electrode interface. When 3,3-diaminobenzidine (DAB) and glucose were introduced, the cascade reaction was initiated by GOx to catalyze the oxidation of glucose, in situ generating H2O2. Simultaneously, the decomposition of the generated H2O2 was greatly promoted by Pt@CuMOFs and hGq as synergistic peroxide catalysts, accompanying with the significant oxidation process of DAB and the formation of nonconductive insoluble precipitates (IPs). As a result, the electron transfer in the resultant sensing interface was effectively hindered and the electrochemical impedimetric signal (EIS) was efficiently amplified. Thus, the high sensitivity of the proposed CEA aptasensor was successfully improved with 0.023 pg mL−1, which may be promising and potential in assaying certain clinical disease related to CEA.

•An impedimetric aptasensor platform was proposed to biosense protein.•PtPd nanowires were used as nanocarriers to promote loading of biomolecules.•Mimicking enzymes MnTMPyP were embedded into dsDNA extended by HCR.•MnTMPyP-dsDNA oxidization of DAB to form insoluble precipitates (IPs).•The electron transfer was hindered by IPs, resulting in amplification of signal.In this study, a sensitive biosensing interface for protein was reported based on nonconductive insoluble precipitates (IPs) by the biocatalysis of manganese(III) meso-tetrakis (4-N-methylpyridiniumyl)-porphyrin (MnTMPyP), which was intercalated into formed double-strand DNA (dsDNA) scaffold triggered by hybridization chain reaction (HCR). In the proposed impedimetric aptasensor, carcinoembryonic antigen (CEA) and its aptamer were used as testing model. PtPd nanowires (PtPdNWs) with large surface area and superior conductivity were employed as nanocarriers to greatly immobilize biomolecules (e.g. CEA aptamers). Then, two DNA hairpins H1 and H2 were introduced to trigger HCR with the assistance of DNA initiator, resulting in the formation of a long dsDNA scaffold. Meanwhile, mimicking enzyme MnTMPyP molecules were embedded into the resultant dsDNA, in situ generating the complex MnTMPyP-dsDNA with peroxidase-like activity. Under the biocatalysis of MnTMPyP-dsDNA, 3,3-diaminobenzidine (DAB) was oxidized to form nonconductive IPs. As a result, the electron transfer between electrode interface and redox probe was vastly hindered, leading to the significant amplification of electrochemical impedimetric signal. So, greatly improved analytical performances of the proposed aptasensor were achieved with a detection limit as low as 0.030 pg mL−1. And the successful assay of CEA in human serum samples enabled the developed biosensing platform to have promising potential in bioanalysis.

In this work, a sensitive electrochemical aptasensor for the detection of thrombin (TB) is developed and demonstrated based on the co-catalysis of hemin/G-quadruplex, platinum nanoparticles (PtNPs) and flower-like MnO2 nanosphere functionalized multi-walled carbon nanotubes (MWCNT–MnO2).

•PDDA–G–MoS2 nanoflowers were firstly used for the fabrication of thrombin aptasensor.•MoS2 was adopted to enhance the surface area of graphene and accelerate the electron transfer.•GOD, PdNPs and hemin/G-quadruplex could amplify the electrochemical signal through synergetic catalysis.•The proposed aptasensor displayed an improved sensitivity.In the present study, with the aggregated advantages of graphene and molybdenum disulfide (MoS2), we prepared poly(diallyldimethylammonium chloride)–graphene/molybdenum disulfide (PDDA–G–MoS2) nanocomposites with flower-like structure, large surface area and excellent conductivity. Furthermore, an advanced sandwich-type electrochemical assay for sensitive detection of thrombin (TB) was fabricated using palladium nanoparticles decorated PDDA–G–MoS2 (PdNPs/PDDA–G–MoS2) as nanocarriers, which were functionalized by hemin/G-quadruplex, glucose oxidase (GOD), and toluidine blue (Tb) as redox probes. The signal amplification strategy was achieved as follows: Firstly, the immobilized GOD could effectively catalyze the oxidation of glucose to gluconolactone, coupling with the reduction of the dissolved oxygen to H2O2. Then, both PdNPs and hemin/G-quadruplex acting as hydrogen peroxide (HRP)-mimicking enzyme could further catalyze the reduction of H2O2, resulting in significant electrochemical signal amplification. So the proposed aptasensor showed high sensitivity with a wide dynamic linear range of 0.0001 to 40 nM and a relatively low detection limit of 0.062 pM for TB determination. The strategy showed huge potential of application in protein detection and disease diagnosis.

Highly sensitive detection of carcinoembryonic antigen (CEA) is very important in clinical diagnosis and treatment assessment of cancers. In this work, we proposed a sensitive and selective electrochemical aptasensor for CEA detection using dendritic Pt@Au nanowires (Pt@AuNWs) as nanocarriers and electrocatalysts. With many advantages such as large specific surface area, good conductivity, excellent electrocatalytic activity and high stability, dendritic Pt@AuNWs were first employed as nanocarriers for immobilizing abundant thiol-terminated CEA aptamer 2 (CEAapt2) and redox-active toluidine blue (Tb), resulting in the formation of AuNWs–CEAapt2–Tb bioconjugate. In the presence of CEA, the proposed bioconjugate was captured onto the electrode surface through “sandwich” tactics. The electrochemical response was then triggered and further enhanced due to the favorable catalysis capacity of dendritic Pt@AuNWs with peroxidase mimic activity for the reduction of H2O2 added into the electrolytic cell, from which an improved sensitivity benefited and was successfully achieved. Under the optimal experimental conditions, the proposed aptasensor exhibited a linear response to CEA in the range of 0.001 ng mL−1 to 80 ng mL−1 and the limit of detection (LOD) is 0.31 pg mL−1. Moreover, the aptasensor exhibited good selectivity, stability and reproducibility, which indicated its potential applications in clinical diagnostics.

In this work, a ‘signal on-off’ electrochemical peptide biosensor was developed for the determination of matrix metalloproteinase 2 (MMP-2) on the basis of target induced cleavage of a specific peptide. The prepared single-stranded DNA–porous platinum nanoparticles–peptide (S1–pPtNPs–P1) bioconjugates were employed as nanoprobes, where the specific peptide (P1, biotin–Gly–Pro–Leu–Gly–Val–Arg–Gly–Lys–Gly–Gly–Cys) was used as a cleavage-sensing element, offering the capability of ‘on-off’ electrochemical signalling for the target MMP-2. As for the construction of the biosensor, S1–pPtNPs–P1 was immobilized on the electrode surface through the conjunction of biotin–streptavidin. Then, hybridization chain reaction (HCR) was triggered to embed the electroactive thionine (Thi). The pPtNPs could effectively catalyze the decomposition of added H2O2, resulting in the electrochemical signal of Thi being enhanced significantly (‘signal on’ state). Upon sensing cleavage with MMP-2, pPtNPs and eletroactive Thi left the electrode surface, leading to an observable decrease in the electrochemical signal of Thi (‘signal off’ state). Compared with other methods of detecting MMP-2, the proposed ‘signal on-off’ electrochemical peptide biosensor exhibited an improved sensitivity with a detection limit of 0.32 pg mL−1 and wide linear range from 1 pg mL−1 to 10 ng mL−1.

In this work, a label-free electrochemical aptasensor for sensitive detection of thrombin was fabricated and characterized. This aptasensor was based on the direct electron transfer of hemin and hemin functionalized reduced graphene oxide hybrid nanosheets (hemin@rGO) as the signal probe. Hemin@rGO with intrinsic peroxidase-like activity could catalyze the reaction of the peroxidase substrate because of the catalytic ability of hemin attached on the graphene surface through π–π interactions. The greatly enhanced sensitivity of the as-prepared aptasensor for thrombin was based on an effective signal amplification strategy. Firstly, the synthesized hemin@rGO nanosheets not only provided a large conductive interface, but also exhibited excellent redox activity with avoidance of an extra electroactive mediator. Secondly, the electrodeposition of Pt nanoparticles (PtNPs) on the resultant electrode surface effectively promoted the electron transfer and amplified the electrochemical response. Thirdly, further enhanced sensitivity was achieved by the outstanding catalytic performance of the horseradish peroxidase as the blocking reagent. On the basis of such a signal amplification strategy, the direct and facile electrochemical aptasensor showed superior electrocatalytic efficiency toward H2O2, and sensitively responded to 0.45 pM thrombin with a linear calibration range from 1 pM to 50 nM. So, the proposed detecting platform for thrombin could be promising for clinical analysis and assays.

•A simple and sensitive electrochemical thrombin aptasensor was developed.•Porous Au@Pd core–shell nanostructures were used as nanocarriers.•Hemin/G-quadruplex, Tb and GOx were abundantly immobilized on the nanocarriers.•Au@Pd core–shell nanostuctures and hemin/G-quadruplex acted as peroxidase mimics.•Synergetic catalysis of GOx, Au@Pd and hemin/G-quadruplex amplified the signal.In this work, a sensitive electrochemical aptasensor for thrombin (TB) based on synergetic catalysis of enzyme and porous Au@Pd core–shell nanostructure has been constructed. With the advantages of large surface area and outstanding catalytic performance, porous Au@Pd core–shell nanostructures were firstly employed as the nanocarrier for the immobilization of electroactive toluidine blue (Tb), hemin/G-quadruplex formed by intercalating hemin into the TB aptamer (TBA) and glucose oxidase (GOx). As a certain amount of glucose was added into the detection cell, GOx rapidly catalyzed the oxidation of glucose, coupling with the local generation of H2O2 in the presence of dissolved O2. Then, porous Au@Pd nanoparticles and hemin/G-quadruplex as the peroxidase mimics efficiently catalyzed the reduction of H2O2, amplifying the electrochemical signal and improving the sensitivity. Finally, a detection limit of 0.037 pM for TB was achieved. The excellent performance of the aptasensor indicated its promising prospect as a valuable tool in simple and cost-effective TB detection in clinical application.

A highly sensitive electrochemical aptasensor for thrombin detection is developed and demonstrated by using porous platinum nanotubes modified with polyamidoamine dendrimers as nanocarriers and electrocatalysts. The proposed strategy affords a low detection limit of 0.03 pM based on enzyme-based signal amplification.

A sensitive and selective electrochemical aptasensor for thrombin detection was constructed based on hemin/G-quadruplex as the signal label and Fe3O4–Au nanocomposites with glucose oxidase (GOx-) and peroxide-mimicking enzyme activity as the signal enhancers. Due to their large surface area and good biocompatibility, Fe3O4–Au nanocomposites were employed to immobilize electroactive hemin/G-quadruplex, which was formed by the conjugation between a single-stranded guanine-rich nucleic acid and hemin. Based on the GOx-mimicking enzyme activity, Au nanoparticles on the surface of the Fe3O4–Au nanocomposites effectively catalyzed the oxidization of glucose in the presence of dissolved O2, accompanied by the production of H2O2. Both the Fe3O4 cores of Fe3O4–Au nanocomposites and hemin/G-quadruplex with H2O2-mimicking enzyme activity could catalyze the reduction of the generated H2O2, which promoted the electron transfer of hemin and amplified the electrochemical signal. The proposed electrochemical aptasensor had a wide dynamic linear range of 0.1 pM to 20 nM with a lower detection limit of 0.013 pM, which provided a promising method for a sensitive assay for the detection of proteins in electrochemical aptasensors.

•A pseudo triple-enzyme cascade amplified aptasensor for thrombin was constructed.•Hemin/G-quadruplex acted as NADH oxidase and HRP-mimicking DNAzyme.•ADH-GSs bionanocomposite increased the immobilized amount of ADH.•Corporate catalysis of ADH and hemin/G-quadruplex realized signal amplification.In this work, a pseudo triple-enzyme cascade amplified electrochemical aptasensor based on hemin/G-quadruplex as signal label for thrombin (TB) was constructed and the amplified electrochemical signal was achieved by the corporate catalysis of alcohol dehydrogenase-graphene sheets (ADH-GSs) bionanocomposite and hemin/G-quadruplex, which simultaneously acted as NADH oxidase and HRP-mimicking DNAzyme. Through “sandwich” reaction, hemin/G-quadruplex labeled gold nanoparticles-ADH-GSs bionanocomposite (AuNPs-ADH-GSs) was captured on electrode surface and thus obtained the electrochemical signal. After the addition of ethanol into the electrolytic cell, ADH availably catalyzed the oxidation of ethanol with the reduction of NAD+ to NADH. Then, hemin/G-quadruplex as NADH oxidase catalyzed the oxidization of NADH, accompanying with the production of H2O2. Simultaneously, hemin/G-quadruplex as HRP-mimicking DNAzyme catalyzed the reduction of the generated H2O2. Such a catalysis strategy greatly promoted the electron transfer of hemin and resulted in the specific enhancement of electrochemical signal. The proposed TB aptasensor achieved a linear range of 1 pM–50 nM with a detection limit of 0.3 pM (defined as S/N=3). In addition, it showed satisfying stability and reproducibility, good specificity and sensitivity, indicating promising application for the detection of various proteins in clinical analysis.

Herein, a strategy was put forward for sensitive label-free electrochemical immunosensor by using silver–graphene oxide (Ag–GO) as redox probe. Initially, a simple, soft reaction conditions and efficient route was designed to in situ reduce silver nanoparticles (AgNPs) onto graphene oxide (GO) by glucose as reducing agent. The obtained nanocomposite gave a pair of well-defined redox peaks with the advantages of good biocompatibility and chemical stability. Furthermore, the GO provided large surface area for assembly of abundant AgNPs with redox activity, which potentially paved sensitive way for immunodetection. Thus, the Ag–GO nanocomposites were used as redox probe to fabricate a sensitive label-free immunosensor for α-1-fetoprotein (AFP). In addition, gold nanoparticles (AuNPs) for immobilization of antibody (anti-AFP) could amplify the electrochemical signal and further enhance the sensitivity of the immunosensor due to its excellent conductivity and large surface area. Under the optimal condition, the anodic peak current linearly responded to the logarithm of AFP concentration in a wide range from 0.01 to 100 ng mL−1 with a low limit of detection of 3 pg mL−1 (S/N = 3). The designed immunosensor displayed the advantages of simple preparation, high sensitivity, good selectivity and satisfactory stability.

•A thrombin aptasensor based on target recycling and ADH catalysis was developed.•ADH was abundantly encapsulated into the MPTS sol with a 3-D network.•The ADH effectively improved the electrochemical signal via the enzyme-catalysis.•The employment of the RecJf exonuclease achieved the target-recycling.•The strategy realized high sensitivity, good stability and reproducibility.In the present study, a sensitive electrochemical aptasensor based on exonuclease-catalyzed target recycling and enzyme-catalysis was developed for thrombin (TB) detection. Firstly, the alcohol dehydrogenase (ADH) was abundantly embedded in the 3-(mercaptopropyl)trimethoxysilane (MPTS) sol with a 3-D network that exhibited tunable porosity and high thermal stability. ADH, as an alcohol oxidase, catalyzed the conversation of alcohol into acetaldehyde coupling with the production of NADH in the presence of NAD+. Then the immobilized gold nanoparticles (AuNPs) could electrocatalyze the oxidation of NADH, finally promoting the redox reaction of the electroactive material methylene blue (MB) labeled on the hybrid double strand DNA (dsDNA). Furthermore, when the mixture of TB and RecJf exonuclease was introduced, TB combined with the thrombin aptamer II (TBA II) and the aptamer–TB complex was formed. And then, the RecJf exonuclease selectively degraded the TBA II from 5′→3′, releasing the target TB into the solution. The free TB was reused to combine with other TBA II to accomplish the target recycling and realize the electrochemical signal amplification. In this way, excellent sensitivity of the aptasensor was obtained. The thrombin aptasensor achieved a detection limit of 1.7 pM (defined as S/N=3) with a linear range from 5 pM to 100 nM. In addition, the proposed aptasensor had good stability and sensitivity, and would become a promising choice for the protein diagnostics in clinical analysis.

A highly sensitive electrochemical aptasensor for thrombin detection is developed and demonstrated by using porous platinum nanotubes modified with polyamidoamine dendrimers as nanocarriers and electrocatalysts. The proposed strategy affords a low detection limit of 0.03 pM based on enzyme-based signal amplification.

In this work, a sensitive electrochemical aptasensor for the detection of thrombin (TB) is developed and demonstrated based on the co-catalysis of hemin/G-quadruplex, platinum nanoparticles (PtNPs) and flower-like MnO2 nanosphere functionalized multi-walled carbon nanotubes (MWCNT–MnO2).

In this work, a label-free electrochemical aptasensor for sensitive detection of thrombin was fabricated and characterized. This aptasensor was based on the direct electron transfer of hemin and hemin functionalized reduced graphene oxide hybrid nanosheets (hemin@rGO) as the signal probe. Hemin@rGO with intrinsic peroxidase-like activity could catalyze the reaction of the peroxidase substrate because of the catalytic ability of hemin attached on the graphene surface through π–π interactions. The greatly enhanced sensitivity of the as-prepared aptasensor for thrombin was based on an effective signal amplification strategy. Firstly, the synthesized hemin@rGO nanosheets not only provided a large conductive interface, but also exhibited excellent redox activity with avoidance of an extra electroactive mediator. Secondly, the electrodeposition of Pt nanoparticles (PtNPs) on the resultant electrode surface effectively promoted the electron transfer and amplified the electrochemical response. Thirdly, further enhanced sensitivity was achieved by the outstanding catalytic performance of the horseradish peroxidase as the blocking reagent. On the basis of such a signal amplification strategy, the direct and facile electrochemical aptasensor showed superior electrocatalytic efficiency toward H2O2, and sensitively responded to 0.45 pM thrombin with a linear calibration range from 1 pM to 50 nM. So, the proposed detecting platform for thrombin could be promising for clinical analysis and assays.