This work presents a heterojunction-mediated photoelectrochemical (PEC) biointerface for selective detection of microcystin-LR (MC-LR) by introducing a direct Z-scheme heterojunction as efficient visible-light-driven photoactive species. Specifically, the Z-scheme type CdTe-Bi2S3 heterojunction was designed and synthesized as an ideal photoactive material, which exhibited higher PEC activity as compared with either CdTe quantum dots or Bi2S3 nanorods due to the improved photogenerated charges separation efficiency of heterojunction. Then the MC-LR aptamer was employed for selective recognition of MC-LR target, which was immobilized on the CdTe-Bi2S3 film by the formation of phosphor-amidate bonds between the phosphate group of aptamer and amino group of the chitosan film on the electrode. The proposed aptasensor showed a photocurrent signal due to the photoactive CdTe-Bi2S3 heterojunction, while the presence of MC-LR resulted in a dose-responsive decrease in PEC response, which allowed the quantification analysis of MC-LR by measuring the photocurrent signal of the fabricated aptasensor. Under optimal conditions, the resulted PEC aptasensor showed wide linear range (0.01–100 pM) and low detection limit (0.005 pM) for MC-LR determination with high selectivity and acceptable reproducibility. Finally, the proposed aptasensing method was successfully applied in MC-LR detection in real water samples.Keywords: Bi2S3 nanorod; CdTe quantum dot; microcystin-LR detection; photoelectrochemical aptasensor; Z-scheme heterojunction;

Deeply understanding the internal mechanism of the photoelectrohemical (PEC) process is conducive to fabricate high-performance PEC biosensors. In this work, we proposed a new insight toward an efficient charge-separation mechanism in high-performance PEC biosensors. Specifically, we disclosed that the lifetimes of photogenerated charge carriers of ultrathin MoS2 nanosheets could be prolonged by approximately millisecond time scales after a proper mole ratio of NGQDs were coupled, leading to the promoted charge separation and a giant photocurrent signal magnification. Benefiting from the dramatic signal amplification and the introduction of acetamiprid aptamer, subfemtomolar level detection of acetamiprid is achieved, which makes our strategy among the most sensitive electronic approaches for PEC-based monitoring of targets. This study was beneficial to further understand the charge-separation mechanism in PEC biosensing, which paved the way for the development of more efficient PEC biosensors.

Graphene quantum dots (GQDs), a type of emerging luminescent quantum dot, have drawn remarkable attention owing to their numerous fascinating properties and wide range of potential applications. Despite the intensive research efforts devoted to GQD fabrication, the mass production of high-quality GQDs in a reproducible and eco-friendly manner still represents a great challenge. Hence, we introduce an environmentally friendly, fast and industrially promising method for generating GQDs in large scale via the ionic liquid (IL)-assisted controllable electrochemical exfoliation of carbon fibers. Interestingly, it is found that the size-dependent optical properties of the as-prepared GQDs can be adjusted by using IL electrolytes with different water contents. For example, volume ratios of H2O/IL of 0%, 15% and 30% generate blue-emitting GQDs (B-GQDs), green-emitting GQDs (G-GQDs) and yellow-emitting GQDs (Y-GQDs), respectively. More interestingly, when pure IL is used as the electrolyte, IL-functionalized GQDs with blue photoluminescence emission (B-GQDs) are generated. These functionalized GQDs can effectively improve the electrochemiluminescence (ECL) performance of the system of Ru(bpy)32+–ECL. Furthermore, we have fabricated a well-designed ECL sensor with satisfactory sensitivity for the determination of pentachlorophenol (PCP). More importantly, this proposed green and large-scale approach provides a promising and extremely flexible platform for the preparation of GQDs with tunable photoluminescence.

Considering that ultraviolet light may cause the denaturation of biomaterials, searching for and engineering innovative and advanced nanomaterials with excellent photoelectrochemical properties under visible light illumination are of great significance in the fundamental understanding and application of photoelectrochemical (PEC) sensors. As a widely applied visible light response material, the applications of Bi2WO6 in PEC fields were restricted because of the rapid recombination of photoinduced electron–hole pairs. In this work, Bi2WO6 functionalized reduced oxide (Bi2WO6–rGO) nanocomposites (NCs) were prepared by a one-step solvothermal method. After optimizing the content of rGO, the Bi2WO6–rGO2.94% NCs displayed enhanced photocurrent intensity (the starting mass ratios of GO to Bi2WO6 = 0.0294), which was nearly 2.7-fold compared to that of pure Bi2WO6 nanoparticles because of the separation of the photoinduced carriers and the enhancement of visible light absorption. Based on the coupling of Pb2+-induced allosteric transition of G-quadruplex DNAzyme and the enzymatic biocatalytic precipitation (BCP), Bi2WO6–rGO2.94% NCs were applied in the construction of a novel PEC sensor for the determination of Pb2+. The as-fabricated PEC sensor exhibited good anti-interference ability and a good linear relationship was obtained between the photocurrent intensity and the logarithm of the Pb2+ concentration over a concentration range from 0.01 to 50 μM and with a detection limit of 3.3 nM (S/N = 3), indicating that Bi2WO6–rGO NCs would be promising materials for PEC sensing.

The authors have coupled ultrafine α-Fe2O3 nanocrystals to N-doped graphene (NG) to obtain a novel material for use in a photoelectrode. The presence of NG is shown to strongly affect the morphology and size of the α-Fe2O3 nanocrystals formed on the NG sheets, and to improve their photoelectrochemical (PEC) activity. Interestingly, the PEC performance of the nanocomposite is closely correlated to the size of the α-Fe2O3 nanocrystals in that small nanocrystals display better PEC properties. The photocurrent of α-Fe2O3-NG is nearly 3.3-fold stronger than that of α-Fe2O3 nanocrystals. Based on the remarkable PEC performance of this nanocomposite, a PEC sensor was constructed for the sensitive determination of 1,4-dihydroxybenzene (HQ). Its photocurrent increases with the HQ concentration in the range from 3.0 nM to 3.3 μM, and the detection limit is 1.0 nM (at an S/N ratio of 3). In our perception, the study presented here can serve as a basis for a better understanding of the relationship between morphologies and PEC performance of such nanomaterials. Conceivably, it may be extended to other PEC sensing system and to other fields associated with nanotechnology.

Photoelectrochemical (PEC) detection is an attractive analytical tool as it allows for an elegant and sensitive assay. However, designing a novel detection strategy to achieve an excellent PEC analytical performance is still highly challenging. Herein we design a novel photoelectrochemical (PEC) chlorpyrifos biosensor based on dual signal amplification strategy coupling dual inhibition effect. Dual signal amplification strategy was achieved by coupling the graphene quantum dots sensitized CuFe2O4 magnetic nanocrystal clusters (GQDs–CuFe2O4 MNCs) with the amplification of enzymolysis products. In this biosensing architecture, the GQDs–CuFe2O4 MNCs prepared by electrostatic adsorption showed nearly 4-fold and 30-fold enhancement photocurrent compared with the pure CuFe2O4 MNCs and GQDs, respectively. And the contact angle measurement demonstrated that the GQDs–CuFe2O4 MNCs exhibited good biocompatibility. Based on all these above advantages, the GQDs–CuFe2O4 MNCs were immobilized on the magnetic electrode surface by a fast and simple magnetism-assisted assembly, and the acetylcholinesterase (AChE) was further coated on the surface of the as-prepared multifunctional electrode. Due to thiocholine (enzymolysis products) acts as a sacrificial electron donor to scavenge the holes, compared with the GQDs–CuFe2O4 MNCs modified electrode in the acetylthiocholine chloride solution, the photocurrent of the resulting AChE-based biosensor was further significantly enhanced. Based on the dual inhibition of AChE activity by chlorpyrifos and the formation of Cu-chlorpyrifos complex hindered the electron transfer of CuFe2O4 MNCs toward the electrode surface, the proposed AChE-based biosensor can be applied to the quantification of chlorpyrifos with a linear range from 0.001 μg mL−1 to 1 μg mL−1 and a detection limit of 0.3 ng mL−1 (S/N = 3). This novel dual signal amplification strategy opens up a new avenue for achieving high sensitivity in the field of PEC biosensing.

•AgBr anchored 3D nitrogen-doped graphene hydrogel were prepared.•Nitrogen doping intrinsically improved the conductivity of 3D graphene.•The 3D porous structure provided a high loading volume for luminol.•AgBr served as the catalyst to amplify ECL performance of luminol.•All-solid-state luminol-ECL Escherichia coli aptasensors were fabricated.It is necessary to develop rapid, simple and accurate detection method for Escherichia coli (E. coli) due to its widely distributed pathogenic bacteria. Herein, we prepared AgBr nanoparticles (NPs) anchored 3D nitrogen-doped graphene hydrogel (3DNGH) nanocomposites with an exceptionally large accessible surface by a simple hydrothermal approach. The as-prepared 3DNGH porous nanocomposite not only showed better conductivity than that of 3D graphene due to introducing nitrogen element into graphene framework, but also provided a high loading volume for immobilizing luminol. Meanwhile the anchored AgBr NPs served as the catalyst can effectively enhance the ECL behavior of luminol. And the resulting luminol/AgBr/3DNGH exhibited more excellent ECL performances, which was about 2, 3, 8 times enhanced respectively, comparing to luminol/AgBr/3DGH, luminol/3DNGH and luminol/AgBr/2DNG. Further, the multifunctional nanoarchitecture was used as the all-solid-state ECL platform for fabricating Escherichia coli aptasensors via glutaraldehyde as crosslinking agent between amine-functionalized E. coli aptamer and luminol/AgBr/3DNGH. Based on the steric hindrance mechanism that E.coli can significantly decrease the ECL intensity, the proposed aptasensor displayed a linear response for E.coli in the range from 0.5 to 500 cfu/mL with an extremely low detection limit of 0.17 cfu/mL (S/N). In addition, this ECL aptasensor possessed great advantages including the simple operation process, low-cost and sensitivity, which provided a promising approach for the E.coli detection in biomedical, food detection and environmental analysis.

The use of ternary heterojunctions can lead to superior performance in photoelectrochemical (PEC) sensing. This can be ascribed to effective separation and reduced recombination probability of photogenerated electron-hole pairs. The authors describe the rational design of ternary heterojunctions comoposed of BiOCl, BiVO4 and nitrogen-doped carbon quantum dots (N-CDs). They exhibit enhanced photocurrent compared to the use of BiOCl/BiVO4, BiOCl, or BiVO4. The new material was used in a sensor platform for detection of the neurotransmitter dopamine (DA). Under zero voltage and visible light excitation, DA can be detected in the 1 pM to 10 μM concentration range, with a 0.3 pM lower detection limit (at an S/N ratio of 3). The sensor has rapid response and was applied to the determination of DA in spiked serum samples. Notably, this work also may assist in a better understanding of the relationship between kind of ternary heterojunctions and PEC performance. Conceivably, it can be extended to other PEC sensor platform and other photocatalytic system associated with photoactive materials.

As a single-atom-thick carbon material with high surface and good conductivity, graphene provides an ideal platform for designing composite nanomaterials for high-performance catalytic system. Herein, we obtained a TiO2-reduced graphene oxide nanocomposite (TiO2-RGO) with graphene oxide and tetrabutyl titanate using a facile in situ hydrothermal method. The merit of this method is that the nanocomposites could be produced directly from graphene oxide in the hydrothermal reaction, where the reduction of graphene oxide and the decoration of TiO2 occurred simultaneously. TiO2 nanoparticles anchored on graphene sheets as spacers to keep the neighboring sheets separated. The in situ growth route provides a desirable platform for constructing graphene-supported nanocomposites with improved properties. As one of the major applications of the nanocomposites, we investigate the performance of as-prepared TiO2-RGO as effective non-light-driven catalysts for activating H2O2 in oxidative degradation of the dye. The system was employed in oxidation degradation not only to reach high degradation efficiency but also to avoid any energy consumption. Meanwhile, the proposed catalytic system processes broad-spectrum oxidative degradation activity for different model organic pollutants. Overall, this work could provide new insights into the fabrication of a TiO2-RGO as high performance catalysts and facilitate their application in the environmental protection issues.Download high-res image (242KB)Download full-size image

•A self-templating synthesis of NGQDs/3DBiOI HHMs was proposed.•A mechanism insight for the formation of NGQDs/3DBiOI HHMs was explored.•The improved photocurrent generation of NGQDs/3DBiOI HHMs was achieved.•The NGQDs/3DBiOI HHMs exhibited enhanced load capacity than pure BiOI.This work presents a self-templating synthetic approach for the synthesis of nitrogen doped graphene quantum dots/3D bismuth oxyiodine (NGQDs/3DBiOI) hybrid hollow microspheres (HHMs) by a facile one-pot solvothermal reaction. In this protocol, the formation of NGQDs/3DBiOI hollow microstructure and the hybridization of NGQDs with BiOI semiconductor were achieved simultaneously in one-pot reaction using the NGQDs as template and dopant, which played a double-acting role in the reaction: (i) to modulate the morphology of BiOI microspheres with special hollow structure; (ii) to hybrid with BiOI for the formation of NGQDs/3DBiOI HHMs. Further investigations revealed that the resulted NGQDs/3DBiOI HHMs exhibit tunable visible-light driven photocurrent generation with varying the amount of NGQDs used in the reaction process, which was ascribed to the simultaneous electron transfer acceleration and bandgap narrowing of the NGQDs/3DBiOI HHMs. Moreover, when evaluated as a matrix for enzyme encapsulation, the resulting NGQDs/3DBiOI HHMs exhibited enhanced load capacity than pure BiOI microspheres by virtue of their particular nanostructure. The design of such three-dimensional NGQDs/3DBiOI HHMs with preferable performance facilitates further multifarious applications for enhanced photocatalysis, enzyme immobilization and biofuels.Download high-res image (341KB)Download full-size image

A novel universal colorimetric sensor for simultaneous dual target detection through DNA-directed self-assembly of graphene oxide and magnetic separation has been designed for the first time.

Interest for accessible and reliable methods for detection of genetically modified organisms (GMOs) has been tremendously growing for providing a proper food label to consumers. Herein, we present a label-free and sensitive photoelectrochemical (PEC) detection of a transgene from the CaMV 35S promoter (P35S, the most commonly inserted gene) by utilizing a Ag/TiO2/nitrogen-doped graphene nanoribbon (Ag/TiO2/N-GNR) ternary composite as a photoactive material. The as-prepared ternary composite was synthesized via a facile one-pot heat treatment method and exhibited a significantly enhanced PEC activity owing to the synergy effect of the surface plasmatic resonance (SPR) of Ag nanoparticles and the rapid electron transfer of N-GNRs. Thus, it can broaden the visible light response and facilitate the charge transfer. Via the enhancement of the PEC response, a label-free PEC sensor for P35S was constructed to monitor the changes in the photocurrent signals of the PEC electrode resulting from DNA hybridization. Under the optimal conditions, a wide linear range for P35S detection was obtained from 0.01 to 500 nM, and the limit of detection (LOD) of the proposed PEC sensor was significantly lowered to 0.003 nM. The present study provides a new approach for the design of a versatile PEC sensor for the detection of nucleic acids with a low abundance for diagnostics and food safety control.

A novel ratiometric photoelectrochemical aptasensor based on the potentiometric resolved photocurrents generated from different PEC active materials was designed for the first time.

•Nano-ensemble CeO2–NG was synthesized by a facile heat-treatment.•CeO2 NCs were well dispersed on NG sheets and CeO2–NG nanocomposites showed good conductivity.•The presence of NG in CeO2–NG nanocomposites facilitated the luminol redox process compared with CeO2 NCs.•CeO2–NG nanocomposites showed strong ECL emission in neutral condition, as the matrix to immobilize enzyme.Ceria nanomaterials for heterogeneous catalysis have attracted much attention due to their excellent properties and have been extensively applied in recent years. But the poor electron conductivity and the aggregation behavior severely affect their electrocatalytic performances. In this paper, we prepared a novel catalyst based on CeO2 nanocrystallines (CeO2 NCs) ensemble-on-nitrogen-doped graphene (CeO2–NG) nanocomposites through a one-step heat-treatment without the need of the precursor. The results confirmed that the high dispersion of CeO2 NCs with the uniform size distribution of about 5 nm on the surface of nitrogen-doped graphene (NG) sheets could be easily obtained via the one-step procedure and the resultant CeO2–NG nanocomposites were an excellent electrode material possessing outstanding electrochemical features for electron transfer. Luminol, an important electroactive substance, was further chosen to inspect the electrocatalytic properties of the as-prepared CeO2–NG nanocomposites. The studies showed that the presence of the NG in CeO2–NG nanocomposites could facilitate the electrochemical redox process of luminol. Compared with pristine CeO2 NCs, the synthesized CeO2–NG nanocomposites can enhance the electrochemiluminescence (ECL) intensity by 3.3-fold and decrease the onset ECL potential for about 72 mV in the neutral condition. Employing above superiority, selecting cholesterol oxidase (ChOx) as the model oxidase, a facile ECL method for cholesterol detection with the CeO2–NG nanocomposites as the matrix to immobilize enzyme ChOx was developed. The results demonstrated CeO2–NG nanocomposites exhibited excellent performances in terms of sensitivity and catalytic activities, indicating that NG-based nanomaterials have great promise in electrocatalytic and enzymatic biosensing fields.

•The 3DNGH is the promising host to load photoactive material and biological receptors.•The ZnO/3DNGH favored high-density immobilization of receptors and penetration of soluble molecules.•ZnO/3DNGH-based 3D PEC biosensing platform was fabricated for the first time.•The ZnO/3DNGH showed a good PEC performance.The aggregation of photoelectrochemical (PEC) active material and biological receptors may affect PEC performances due to limited accessible surface areas. To solve the problem, here we introduced 3D nitrogen-doped graphene hydrogel (3DNGH) into PEC sensing for the first time. 3DNGH not only showed better conductivity than that of 3D graphene due to introducing nirtrogen element into graphene framework, but also provided a high loading amount for PEC active nanomaterial and biological receptors with the porous structure. ZnO/3DNGH was prepared via the hydrothermal treatment. Compared to ZnO/3DGH and ZnO/2DNG, the photocurrent under visible light was greatly improved due to the enhanced light adsorption and accelerated charge transfer. Then ZnO/3DNGH was used to immobilize enzymes to construct a PEC biosensing platform and exhibited good performances. The good result indicated 3DNGH is the promising host for developing PEC biosensors in biomedical and environmental analysis.

•The t-SG/ZnO was fabricated by a facile thermal-treatment strategy.•In this nanoarchitecture, the S-bonding configuration was single thiophene-S.•The t-SG/ZnO exhibited faster interfacial charge transfer and narrower band gap.•The t-SG/ZnO showed better PEC property that of NG/ZnO and GR/ZnO.•A novel kind of “on-off-on” PEC aptasensor for acetamiprid detection was projected.Improving inherent performance of photoactive materials and designing a novel detection strategy are crucial for achieving excellent photoelectrochemical (PEC) aptasensor. Herein, we present a facile thermal-treatment strategy for fabricating thiophene-sulfur-doped graphene/ZnO nanocomposite (t-SG/ZnO). In this nanoarchitecture, pure thiophene-sulfur-doped graphene (t-SG) acted as a novel enhanced carrier, which can effectively improve the visible light photoactivity and photostability of ZnO nanoplates by enhancing the interfacial charge transfer and decreasing the band gap of pure ZnO nanoplates. The as-prepared t-SG/ZnO nanocomposite exhibited higher photocurrent intensity, which was about 1.5 times and 2.6 times than that of nitrogen doped graphene/ZnO and graphene/ZnO, respectively. Furthermore, we have fabricated an “on-off-on” PEC aptasensing strategy for sensitive and selective determination of acetamiprid based on the outstanding PEC performance of t-SG/ZnO by using the aptamer technique as specific recognition. This PEC aptasensing strategy not only gives insights into using t-SG as a novel sensibilizer to improve the PEC nature of semiconductor but also offers a new PEC aptasensor platform for acetamiprid direct detection. This proposed method provides a promising flexible platform for pesticide detection.Download high-res image (137KB)Download full-size image

•A disposable aptasensing device by integrating micro-cell and SPCE was fabricated.•Densely electrodeposited AuNPs on SPCE serves as immobilization matrices for aptamer.•This aptasensor for FB1 has a wide linear range and a low detection limit.•The aptasensing device is simple in operation and less reagent consumption.•This strategy opens new avenue for other targets detection with specific aptamer.A disposable aptasensing device for specific detection of fumonisin B1 (FB1), the most toxic of fumonisin B-series, has been fabricated. In this design, the pretreated screen-printed carbon electrode (SPCE) has been firstly covered by a polydimethylsiloxane (PDMS) film with a hole to construct a micro-cell with the conventional three electrodes at the bottom. Subsequently, well-dispersed gold nanoparticles (AuNPs) have been electrodeposited on the working electrodes to serve as excellent matrices for thiolated aptamer immobilization. Since a single nanoparticle could be conjugated with a large number of aptamer probe, the dense decoration of AuNPs on SPCE provided abundant binding sites for aptamer anchoring, finally enhancing the impedance signal effectively. A high affinity between FB1 and its aptamer has been demonstrated by a small association constant (Ka) of 1.19 × 109 M−1 calculated by Langmuir adsorption isotherm. The developed aptasensor showed a good linearity in the range from 10 pg mL−1 to 50 ng mL−1 with a low detection limit of 3.4 pg mL−1 (S/N = 3). The developed aptasensing device is cost-effective, simple in operation, high-sensitive, less reagent consumption, and can be easily expand to other mycotoxins if the specific aptamer is available.Download high-res image (164KB)Download full-size image

The development of highly efficient visible-excited charge separation photo active materials has attracted great attention for solving the global energy crisis and environmental problems. In this paper, p-type BiOBr nanoplates decorated n-type nitrogen doped graphene (BiOBr-NGR) composites are constructed by a facile wet chemical method. The formation of p-n junctions was beneficial to the efficient visible-excited charge transfer, and effectively restrains the recombination of photoinduced electron–hole pairs, resulting enhanced photoelectrochemical (PEC) performance. In particular, it is shown by means of the transient-state surface photocurrent responses that the photocurrent intensity of the as-fabricated composites exhibited 2.6 times higher than that of pristine BiOBr. Based on the robust photocurrent signal, a novel PEC sensor based on BiOBr-NGR was established for sensitive and selective detection of chlorpyrifos. The as-fabricated PEC sensor demonstrates many advantages such as wide linear range (5 pg mL−1–11.6 ng mL−1), low detection limit (1.67 pg mL−1, S/N = 3), and remarkably convenient, which provides a general format for chlorpyrifos detection in food and environment analysis.

The development of novel detection methodologies in electrochemiluminescence (ECL) aptasensor fields with simplicity and ultrasensitivity is essential for constructing biosensing architectures. Herein, a facile, specific, and sensitive methodology was developed unprecedentedly for quantitative detection of microcystin-LR (MC-LR) based on three-dimensional boron and nitrogen codoped graphene hydrogels (BN-GHs) assisted steric hindrance amplifying effect between the aptamer and target analytes. The recognition reaction was monitored by quartz crystal microbalance (QCM) to validate the possible steric hindrance effect. First, the BN-GHs were synthesized via self-assembled hydrothermal method and then applied as the Ru(bpy)32+ immobilization platform for further loading the biomolecule aptamers due to their nanoporous structure and large specific surface area. Interestingly, we discovered for the first time that, without the aid of conventional double-stranded DNA configuration, such three-dimensional nanomaterials can directly amplify the steric hindrance effect between the aptamer and target analytes to a detectable level, and this facile methodology could be for an exquisite assay. With the MC-LR as a model, this novel ECL biosensor showed a high sensitivity and a wide linear range. This strategy supplies a simple and versatile platform for specific and sensitive determination of a wide range of aptamer-related targets, implying that three-dimensional nanomaterials would play a crucial role in engineering and developing novel detection methodologies for ECL aptasensing fields.

Designing and engineering different material composition to form heterojuction during light illumination is of significance in the fundamental understanding and application of photoelectrochemical (PEC) sensors. In this work, WO3 nanoparticles decorated ultrathin graphite-like carbon nitride (utg-C3N4) semiconductor nanoheterostructures were engineered by a facile thermal treatment method. Such type II band alignment in these two semiconductor systems allows electrons from photoexcited utg-C3N4 to be transferred into WO3 and holes to accumulate at utg-C3N4, which boosted the charge transfer and decreased charge carrier recombination in the coupled system, resulting enhanced PEC performance. Based on the excellent PEC performances of the as-prepared utg-C3N4/WO3, a high sensitivity PEC sensor was fabricated for glucose assay. Under optimal conditions, the as-fabricated PEC sensor demonstrates many advantages such as low detection limit (0.1 μM, S/N = 3), wide linear range (0.01 ∼ 7.12 mM) and remarkably convenient, which provides a general format for glucose detection in blood serum.

•A facile strategy for preparing Lcys-capped rQDs based hybrid spheres was reported.•Lcys serves as the stabilizer of rQDs and primary amine provider to react with TNT.•One can perform onsite visual determination of TNT by using such probe.•The nanosensor exhibited a wide linear range and a low detection limit.•This sensing strategy can be fully integrated in a filter paper-based assay for TNT.New strategies for onsite determination of trace 2,4,6-trinitrotoluene (TNT) explosives have become a research hotspot for homeland security needs against terrorism and environmental concerns. Herein, we designed a ratiometric fluorescence nanohybrid comprising 3-mercaptopropionic acid-capped green-emitting CdTe quantum dots (gQDs) encapsulated into SiO2 sphere and l-cysteine (Lcys)-capped red-emitting CdTe QDs (rQDs) conjugated onto SiO2 surface. The surface Lcys can be used as not only the stabilizer of the rQDs but also the primary amine provider which can react with TNT to form Meisenheimer complexes. Without any additional surface modification procedure, the fluorescence of rQDs equipped with Lcys was selectively quenched by TNT because electrons of the rQDs transferred to TNT molecules due to the formation of Meisenheimer complexes. Meanwhile, the embedded gQDs always remained constant. Upon exposure to increasing amounts of TNT, the fluorescence of rQDs could be gradually quenched and consequently the logarithm of the dual emission intensity ratios exhibited a good linear negative correlation with TNT concentration over a range of 10 nM–8 μM with a low detection limit of 3.3 nM. One can perform onsite visual determination of TNT with high resolution because the ratiometric fluorescence nanosensing system exhibited obvious fluorescence color changes. This sensing strategy has been successfully applied in real samples and already integrated in a filter paper-based assay, which enables potential fields use application featuring easy handling and cost-effectiveness.

•Both NGQDs and AgNPs were selected as the novel FRET donor-acceptor pairs.•The proposed homogeneous FRET assay was developed for CaMV35S detection.•The resulting method could identify 0.5% containing transgenic soybean sample.•This assay was inexpensive, simple and highly sensitive.In this work, a novel homogeneous assay for DNA quantitative analysis based on förster resonance energy transfer (FRET) was developed for cauliflwer mosaic virus 35s (CaMV35S) promoter of transgenic soybean detection. The homogenous FRET of fluorescence signal was fabricated by DNA hybridization with probe modified nitrogen-doped graphene quantum dots (NGQDs) and silver nanoparticles (AgNPs), which acted the donor-acceptor pairs for the first time. The highly efficient FRET and unique properties of the NGQDs made the proposed FRET system as a functionalized detection platform for labelling of DNA. Upon the recognition of specific target DNA (tDNA), the FRET between NGQDs and AgNPs was triggered to produce fluorescence quenching, which could be used for tDNA detection. The fabricated homogeneous FRET assay displayed a wide linear range of 0.1–500.0 nM and a low limit of detection 0.03 nM for the detection of CaMV35S (S/N = 3). This proposed biosensor revealed high specificity to detect tDNA, with acceptable intra-assay precision and excellent stability. This method was successfully applied to identify the real sample of 0.5% containing transgenic soybean, which achieved the most of national law regulations. This assay was further validated by polymerase chain reaction as the genetically modified organisms, suggesting that the proposed FRET system is a feasible tool for the further daily genetically modified organism detection.

•A simple, rapid and label-free biosensor for detection of GM soybean was proposed.•The DNA biosensor was constructed without multiple modified or labeled procedures.•Wide linear range and low detection limit for CaMV 35S detection was obtained.•The proposed method has the merits of good selectivity, reproducibility and stability.•The DNA biosensor showed satisfactory results to discriminate GM soybean samples.We report a simple and label-free electrochemical impedimetric DNA biosensor for genetically modified (GM) soybean detection by recognizing the Cauliflower Mosaic Virus 35S (CaMV 35S). In the detection system, gold nanoparticles decorated multiwalled carbon nanotube-reduced graphene oxide nanoribbons were employed to anchor the probe single-stranded DNA. When the target DNA fixed on the modified electrode surface via hybridizing reaction, the impedimetric signal showed a growing tendency due to the formed double-stranded DNA restraining the electron transfer process. Under optimal conditions, the increased impedimetric signal of the proposed DNA biosensor was linear with the logarithm of the target DNA concentrations in the range of 1 × 10− 16 M–5 × 10− 10 M with a low detection limit of 3.3 × 10− 17 M. Moreover, the biosensor possessed excellent selectivity for discriminating complementary sequences from mismatched DNA as well as satisfactorily applied for practical detection of GM soybean samples.

This work reports a facile approach to achieve the immobilization of graphene quantum dots (GQDs) by one-step electrodeposition and the electrochemiluminescence (ECL) behaviors of the graphene quantum dots-chitosan (GQDs-CHIT) film was investigated with peroxydisulfate (K2S2O8) solution as coreactant. Compare with the traditional dispensing method, the GQDs-CHIT/Au electrode by one-step electrodeposition showed more stable ECL signal. And the ECL signal of GQDs-CHIT modified electrode in K2S2O8 solution was about 11-fold enhanced than that of bare electrode with the ECL onset potential positive shifted from − 1.03 V to − 0.82 V. Based on the above, an ECL sensor for K2S2O8 determination was fabricated. The as-prepared ECL K2S2O8 sensor shows wide linear response of 0.01–150 mM with the detection limit 3.3 μM (S/N = 3). Moreover, we expect this method for the immobilization of GQDs can open up new prospects for the utilization of GQDs in electrochemical sensors.

•AuNPs functionalized silica-coated iron oxide magnetic NPs and quantum dots modified graphene/AuNPs were fabricated.•A dual signal amplification strategy by using these two nanocomposites was constructed.•An aptasensor for OTA detection was designed and exhibited a wide linear range and an extremely low detection limit.Ochratoxin A (OTA) is one of the most toxic food contaminant mycotoxin, which can cause nephrotoxicity, teratogenicity, and carcinogenicity activity. Here an ultrasensitive electrochemical aptasensor for OTA was successfully fabricated. This aptasensor was constructed by combining nanocomposites of gold nanoparticles (AuNPs) functionalized silica-coated iron oxide magnetic nanoparticles (mSiO2@Au) and cadmium telluride quantum dots (CdTe QDs) modified graphene/AuNPs nanocomposites (GAu/CdTe). The as-prepared aptasensor exhibited a wide linear range (0.2 pg mL− 1–4 ng mL− 1), and an extremely low detection limit of 0.07 pg mL− 1 (S/N = 3). This work provides a novel strategy for the ultrasensitive detection of various target molecules and would have great potential in food safety monitoring and clinical diagnosis.

Controllable integration of platinum nanoparticles (PtNPs) and a carbonaceous material is a promising strategy to obtain cost-effective and highly efficient nano-catalysts. Three-dimensional (3D) graphene-based aerogel is considered as an ideal catalyst support because it not only possesses the superior properties of graphene, but also can provide a high loading volume with hierarchical 3D porous architectures. In this paper, PtNP-decorated 3D nitrogen-doped graphene aerogel was prepared through a one-pot hydrothermal route for the first time. Compared to PtNP-decorated 3D graphene aerogel or PtNP-decorated 2D graphene, this nanocomposite shows excellent electrocatalytic activity because of the nitrogen doping and 3D porous structure.

•BiOBrNFs/NG p–n heterojunction was utilized as efficient PEC transducer.•Photocurrent of BiOBrNFs/NG heterojunction was 4.6-fold higher than that of BiOBrNFs.•The BiOBrNFs/NG was to immobilize the MC-LR aptamer for PEC analysis.•The proposed method was used to detect MC-LR in fish samples.The presence of microcystins in fish has been augmenting the risk of toxicity to animal and human health. Herein, a selective and sensitive method for detecting microcystin-LR (MC-LR) in fish samples by integrating the photoelectrochemical (PEC) technique and the specific recognition ability of aptamer was developed. Specifically, as an efficient PEC transducer, the BiOBr nanoflakes/N-doped graphene p–n heterojunction electrode was utilized as the aptamer immobilization platform via the π–π stacking interaction, which would be a biosensor enabling the convenient and exquisite PEC analysis. Subsequently, the PEC response of constructed aptasensor was specific binding to MC-LR. Other isoforms did not interfere with the detection process, and thus, it could be applied for the highly selective determination of MC-LR level. Under the optimized condition, the PEC signal versus the logarithm of the MC-LR concentration was in good linear relationship ranging from 0.1 pM to 100 nM with detection limit about 0.03 pM. The constructed method was employed to analyze fish samples collected from the local supermarket. The overall analytical recovery of MC-LR in the fish matrices ranged from 97.8 to 101.6%, with relative standard deviation (RSD) of 2.52–5.14%, implying it would have great potential in farm product analysis.

•NGR/Ag-TiO2 nanocomposites were prepared by a facile one-pot hydrothermal route.•The photocurrent of NGR/Ag-TiO2 exhibited 18.2 times higher than that of pure TiO2.•A novel kind of “on-off-on” PEC aptasensor was established.•The proposed sensor showed a wide linear range, a low detection limit, and etc.Charge separation is crucial for increasing the performances of semiconductor-based materials in many photoactive applications. In this paper, we designed novel nanocomposites consisting of TiO2 nanocrystals, Ag nanoparticles (NPs) and nitrogen doped graphene (NGR) via a facile one-pot hydrothermal route. The as-prepared ternary nanocomposites exhibited enhanced photoelectrochemical (PEC) performances owing to the introduction of Ag NPs and NGR, which increase the excitons’ lifetime and improve the charge transfer. In particular, it is shown by means of the transient-state surface photocurrent responses that the photocurrent intensity of the as-fabricated composites exhibited 18.2 times higher than that of pristine TiO2. Based on the robust photocurrent signal, a new kind of “on-off-on” PEC aptasensor was established with the assistance of Pb2+ aptamer, which integrates the advantages of low background signal and high sensitivity. Under optimal conditions, a wide linear response for Pb2+ detection was obtained from 1 pM to 5 nM as well as a detection limit down to 0.3 pM. With its simplicity, selectivity, and sensitivity, this proposed strategy shows great promise for Pb2+ detection in food and environment analysis.

To develop novel resonance energy transfer (RET) system can provide opportunities for the goal of sensitive and inexpensive detection of aptamer-related targets such as DNA and microRNA, protein, and small-molecule. In this work, a novel RET system from CdTe quantum dots (QDs) to Au nanorods (Au NRs) was fabricated, by employing MWCNTs/reduced graphene oxide nanoribbons (MWCNTs/rGONRs) as the photoelectrochemical (PEC) signal amplifier and ideal support for QDs anchored. The photocurrent signal of CdTe QDs was amplified for ∼3.3-fold due to the sensitization effect of MWCNTs/rGONRs, and the proposed CdTe-MWCNTs/rGONRs exhibited the typical fluorescence emission at 713 nm, which showed good spectral overlap with the UV–vis absorption spectrum of Au NRs. Furthermore, a visible-light-driven “on-off-on” PEC sensing strategy for sensitive and selective determination of acetamiprid was designed. Under optimal conditions, the resulting PEC aptasensor was found to be linearly proportional to the logarithm of target acetamiprid concentration in the range from 0.5 pM to 10 μM with a detection limit of 0.2 pM. Moreover, the proposed sensor displayed high selectivity and good reproducibility, and has been successfully applied in the direct detection of acetamiprid in real food samples. This method could resist environmental interfering agents and be extended for sensitive and reliable detection of a wide range of analytes in complex samples.

•Photoelectrochemical CaMV35S biosensor as a new method was fabricated.•SiO2@CdTe quantum dots core-shell nanoparticles acted as signal indicators.•The biosensors could discriminate the transgenic from non-transgenic soybean.•Simple preparation, good selectivity and high sensitivity were obtained.A methodology for detection of the Cauliflower Mosaic Virus 35S(CaMV35S) promoter was developed to distinguish transgenic from non-transgenic soybean samples by using photoelectrochemical (PEC) biosensor. In this PEC biosensing system, the as-prepared gold nanoparticles-reduced graphene oxide acted as a nanocarrier to immobilize the thiol-functional probe (probe1), and the SiO2@CdTe quantum dots (QDs) core-shell nanoparticles tagged with the amino-functional probe (probe2) acted as signal indicators, respectively. In the presence of target DNA (tDNA) of CaMV35S, the binding of tDNA with probe1 and probe2 through the high specific DNA hybridization led to the fabrication of sandwich structure, and thus the high loading of the signal indicators SiO2@CdTe QDs at the electrode surface, which increased the PEC signal. The increased PEC signal depended on the concentration of tDNA, and a wide linear range from 0.1 pM to 0.5 nM with low detection limit of 0.05 pM was obtained. In addition, the PEC biosensor has been successfully used for discriminating transgenic soybean from non-transgenic samples, which was consistent with the polymerase chain reaction (PCR) results, suggesting the proposed PEC biosensor is a feasible tool for the further daily genetically modified organism detection.

We report on an in-situ method for fabricating Cu2O nanospheres decorated with graphene quantum dots (GQDs-Cu2O nanospheres). The material was characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. Further, a novel strategy to amplify the electrochemiluminescence (ECL) signal of luminol system based on the GQDs-Cu2O nanospheres has been investigated. Compared to the use of plain Cu2O nanospheres, the incorporation of GQDs improves the catalytic performance of Cu2O nanospheres towards luminol oxidation effectively. This is attributed to the improved electron transfer capability of GQDs. Compared to the Cu2O nanosphere modified electrode, the ECL intensity of luminol was enhanced 3.5-fold at the GQDs-Cu2O nanosphere modified electrode, with the ECL onset potential negatively shifted by 130 mV. Based on these findings, a method was developed for selective determination of the pesticide pentachlorophenol (PCP) which exerts an inhibition effect on the ECL. The assay displays a linear response in the 0.02 to 300 ng mL−1 concentration range, with a detection limit of 6.6 pg mL−1 (at an S/N ratio of 3).

In this work, hollow carbon nanospheres (HCNS) were prepared, followed by the introduction of gold nanoparticles (AuNPs) on the HCNS surface, and then functionalization with per-6-thio-β-cyclodextrin (CD) based on the formation of “Au–S” bond, resulting in a novel cyclodextrin/carbon-based nanohybrid (CD–AuNPs/HCNS), which possesses the unique properties of HCNS (excellent electrochemical properties and large surface area), CD (high host–guest recognition and water-solubility) and AuNPs (excellent electrocatalytic activity). The obtained CD–AuNPs/HCNS nanohybrids were characterized by scanning electron microscopy, transmission electron microscopy, inductively coupled plasma-atomic emission spectroscopy, Fourier transform infrared spectroscopy and electrochemical methods. Furthermore, CD–AuNPs/HCNS were applied in the simultaneous electrochemical sensing of o-dihydroxybenzene (o-DHB) and p-dihydroxybenzene (p-DHB) (both o- and p-DHB have similar structures and coexist in environment; moreover, they are toxic to humans and difficult to degrade). Under the optimum conditions, the detection limits of o- and p-DHB obtained in this work are 0.01 and 0.02 μM, respectively.

In this study, multiwalled carbon nanotube@reduced graphene oxide nanoribbon (MWCNT@rGONR) core–shell heterostructures have been synthesized by the facile unzipping of MWCNTs and subsequent chemical reduction with hydrazine. MWCNTs with diameter <10 nm were selected as the starting material to maintain narrow ribbons <30 nm wide with a few-layer structure. The most important discovery is that the resulting MWCNT@rGONR heterostructures possess intrinsic peroxidase-like activity, 15.9 times higher than that of MWCNTs and 8.4 times higher than that of their unreduced form. The nature of the peroxidase-like activity of the MWCNT@rGONR heterostructures can be attributed to the acceleration of their electron-transfer process and the consequent facilitation of ˙OH radical generation. Kinetic analysis demonstrates that the catalytic behavior is in accordance with typical Michaelis–Menten kinetics and the obtained kinetic parameters indicate that the MWCNT@rGONR heterostructures display a higher affinity for both H2O2 and 3,3,5,5-tetramethylbenzidine than that of horseradish peroxidase. On this basis, we have employed the MWCNT@rGONR heterostructures as novel biosensing platforms to develop a simple, sensitive, and selective colorimetric biosensor for free cholesterol determination. This work will facilitate the formation of MWCNT@rGONR heterostructures with narrow ribbons and the utilization of their intrinsic peroxidase-like activity in biotechnology and medical diagnostics.

The design and exploitation of photoelectrochemical (PEC) sensors with advanced nanomaterials is of great importance to achieving the goal of sensitive and inexpensive detection. In this paper, a series of bismuth phosphate (BiPO4) functionalized reduced graphene oxide (BiPO4–rGO) nanocomposites (NCs) were prepared using a one-step solvothermal method. Compared with the pure BiPO4 nanoparticles (NPs), all of the as-prepared BiPO4–rGO NCs with different starting mass ratios of graphene oxide (GO) to BiPO4 showed an enhanced PEC response. On this basis, the BiPO4–rGO0.03 NCs (the starting mass ratio of GO to BiPO4 = 0.03) with the best PEC response were used for the PEC determination of chlorpyrifos. With the addition of chlorpyrifos, the formation of a Bi–chlorpyrifos complex on the BiPO4 NPs gave rise to an increase in steric hindrance which caused the electron transfer of BiPO4 NPs to trail off towards the electrode surface, and consequently resulted in an obvious decrease in photocurrent. The designed PEC sensor displayed a linear response for chlorpyrifos in the range from 0.05 to 80 ng mL−1 with a low detection limit of 0.02 ng mL−1 (S/N = 3). The common interferents such as methyl parathion, pentachlorophenol, and carbaryl had no obvious influence on the detection of chlorpyrifos, although these substances were reported to influence the PEC sensing of chlorpyrifos to some extent. The applicability of this method was also investigated by the determination of chlorpyrifos in wastewater samples with satisfactory results. Thus, it is expected that the resulting BiPO4–rGO NCs can serve as a potential photoactive material for PEC sensing related applications.

Heteroatom doping enables graphene with novel properties and thus may broaden the potential of graphene-based materials. In this paper, novel ZnO-nanocrystal-decorated nitrogen-doped graphene (N-GR) composites were prepared through a one-step thermal-treatment route using glycine as the nitrogen source. ZnO nanocrystals with a size about 8 nm were well-dispersed and tightly anchored on the N-GR sheet. Compared with ZnO-nanocrystal-decorated undoped graphene, the ZnO/N-GR nanocomposites could not only enhance the electrochemiluminescence (ECL) intensity by 4.3-fold but also moved the ECL onset potential positively for ∼200 mV. All these results could be ascribed to the presence of nitrogen in graphene which decreased the barrier of ZnO nanocrystals reduction. Furthermore, the ECL sensor based on ZnO/N-GR nanocomposites was fabricated for the ultrasensitive detection of pentachlorophenol (PCP). This recyclable and eco-friendly sensor has excellent performances including wide linear range (0.5 pM to ∼61.1 nM), low detection limit (0.16 pM, S/N = 3), good selectivity, and stability, which is a promising sensor for practical application in environment analysis.Keywords: detection; electrochemiluminescence; nitrogen-doped graphene; pentachlorophenol; ZnO nanocrystal

We proposed a facile method to prepare the nitrogen-doped graphene quantum dots (NGQDs) doped silica (NGQDs@SiO2) nanoparticles (NPs). The NGQDs@SiO2 NPs were further explored as a versatile signal indicator for ochratoxin A (OTA) aptasensing by combination with electrochemiluminescence (ECL) and fluorescence (FL) detection. In this strategy, the core–shell Fe3O4@Au magnetic beads (MBs) acted as a nanocarrier to immobilize the thiolated aptamer specific for OTA, and the amino modified capture DNA (cDNA) was efficiently tagged with NGQDs@SiO2 NPs. The multifunctional aptasensor was thus fabricated by assembly of the NGQDs@SiO2 NPs onto the surface of Fe3O4@Au MBs through the high specific DNA hybridization between aptamer and cDNA. Upon OTA incubation, the aptamer linked with Fe3O4@Au MBs preferred to form an aptamer–OTA complex, which resulted in the partial release of the preloaded NGQDs@SiO2 NPs. The more OTA molecules in the detection system, the more NGQDs@SiO2 NPs were released into the bulk solution and the less preloaded NGQDs@SiO2 NPs were accumulated on the magnetic electrode surface. This provided a dual channel for OTA detection by combination with the enriched solid-state ECL and homogeneous FL detection. The FL assay exhibits a wide dynamic range and is more reproducible due to the homogeneous detection while the ECL assay possesses a lower detection limit and is preferable by using a cheaper instrument. One can obtain a preliminary screen from FL assay and a more accurate result from ECL assay. Integrating the virtues of dual analytical modality, this aptasensing strategy well-balanced the rapidity, sensitivity, and dynamic range, making it promising to other targets with aptamer sequences.Keywords: aptasensor; electrochemiluminescence; fluorescence; nitrogen-doped graphene quantum dots; ochratoxin A; silica

Electrochemiluminescence (ECL), a powerful analytical technique, was combined with the “ON1–OFF–ON2” strategy based on the chemical reactions and specific binding among different small chemical compounds for the highly sensitive assay of nonelectroactive organophosphate pesticides.

AgBr nanoparticles anchored nitrogen-doped graphene nanocomposites were designed to obtain enhanced electrochemiluminescence intensity and better stability, and further applied in electrochemiluminescence detection for the first time.

•Quantitatively study the inhibitors of Cu2+/Zn2+ induced β-amyloid aggregation.•The half maximal inhibitory concentrations (IC50) of inhibitors were obtained.•This method simplifies and reduces the cost of the inhibitors screening procedure.•This high throughput technology is helpful for anti-dementia drugs discovery.In this paper, a kind of gold nanoparticle (GNP)-based colorimetric assay has been developed for studying the reversible interaction of β-amyloid peptide (Aβ) with Cu2+ and Zn2+, and quantitatively analyzing four inhibitors (i.e., EDTA, EGTA, histidine and clioquinol) of Cu2+/Zn2+ induced Aβ assembly. The inhibition efficiencies (e.g., half maximal inhibitory concentration, IC50 value) of these inhibitors could be measured in this work. As far as we know, these IC50 values were reported at the first time. In this assay, the streptavidin conjugated GNPs (SA-GNPs) were employed as indicators to monitor the Cu2+/Zn2+ induced aggregating/disaggregating behaviors of biotin modified β-amyloid 1–16 peptides (Aβ1–16(biotin)). Because of high affinity of streptavidin (SA) with biotin, the aggregating/disaggregating of Aβ1–16(biotin) results in the significant color change of SA-GNPs. Furthermore, we demonstrate that the assay can be used as an effective tool for designing anti-dementia drugs through quantitative analysis of the interactions of four representative inhibitors with Cu2+/Zn2+ induced Aβ assembly.

•A facile strategy for preparing GQDs based core-satellite hybrid spheres was reported.•Such spheres can be used as the ratiometric fluorescence probe for Hg2+ detection.•The Hg2+ content can be easily distinguished by the naked eye.•The sensor shows high sensitivity and selectivity toward Hg2+ detection.•The ratiometric probe is of good simplicity, low toxicity, and excellent stability.We herein proposed a simple and effective strategy for preparing graphene quantum dots (GQDs)-based core-satellite hybrid spheres and further explored the feasibility of using such spheres as the ratiometric fluorescence probe for the visual determination of Hg2+. The red-emitting CdTe QDs were firstly entrapped in the silica nanosphere to reduce their toxicity and improve their photo and chemical stabilities, thus providing a built-in correction for environmental effects, while the GQDs possessing good biocompatibility and low toxicity were electrostatic self-assembly on the silica surface acting as reaction sites. Upon exposure to the increasing contents of Hg2+, the blue fluorescence of GQDs can be gradually quenched presumably due to facilitating nonradiative electron/hole recombination annihilation. With the embedded CdTe QDs as the internal standard, the variations of the tested solution display continuous fluorescence color changes from blue to red, which can be easily observed by the naked eye without any sophisticated instrumentations and specially equipped laboratories. This sensor exhibits high sensitivity and selectivity toward Hg2+ in a broad linear range of 10 nM–22 μM with a low detection limit of 3.3 nM (S/N = 3), much lower than the allowable Hg2+ contents in drinking water set by U.S. Environmental Protection Agency. This prototype ratiometric probe is of good simplicity, low toxicity, excellent stabilities, and thus potentially attractive for Hg2+ quantification related biological systems.

•The GQDs–TiO2 could prevent GQDs assembling and achieve the immobilization of GQDs.•The GQDs–TiO2 showed synergistic amplification on the PEC in the visible region.•The PEC sensor for sensitive and selective detection of dopamine was constructed.•The sensor showed wide linear response and low detection limit for dopamine detection.We have demonstrated a facile approach for fabricating graphene quantum dots–TiO2 (GQDs–TiO2) nanocomposites by a simple physical adsorption method. Compared with pure GQDs and TiO2 nanoparticles (NPs), the as-prepared GQDs–TiO2 nanocomposites showed enhanced photoelectrochemical (PEC) signal under visible-light irradiation. The photocurrent of GQDs–TiO2/GCE was nearly 30-fold and 12-fold enhancement than that of GQDs/GCE and TiO2/GCE, respectively, which was attributed to the synergistic amplification between TiO2 NPs and GQDs. More interestingly, the photocurrent of GQDs–TiO2 nanocomposites was selectively sensitized by dopamine (DA), and enhanced with the increasing of DA concentration. Further, a new PEC methodology for ultrasensitive determination of DA was developed, which showed linearly enhanced photocurrent by increasing the DA concentration from 0.02 to 105 μM with a detection limit of 6.7 nM (S/N = 3) under optimized conditions. This strategy opens up a new avenue for the application of GQDs-based nanocomposites in the field of PEC sensing and monitoring.

A color change observable by the naked eye to indicate the content of an analyte is considered to be the most conceivable way of various sensing protocols. By taking advantage of the Förster resonance energy transfer (FRET) principles, we herein designed a dual-emission ratiometric fluorescent aptasensor for ochratoxin A (OTA) detection via a dual mode of fluorescent sensing and onsite visual screening. Amino group-modified OTA's aptamer was firstly labeled with the green-emitting CdTe quantum dots (gQDs) donor. The red-emitting CdTe QDs (rQDs) which were wrapped in the silica sphere could serve as the reference signal, while the gold nanoparticle (AuNP) acceptors were attached on the silica surface to bind with the thiolated complementary DNA (cDNA). The hybridization reaction between the aptamer and the cDNA brought gQD–AuNP pair close enough, thereby making the FRET occur in the aptasensor fabrication, while the subsequent fluorescence recovery induced by OTA was obtained in the detection procedure. Based on the red background of the wrapped rQDs, the aptasensor in response to increasing OTA displayed a distinguishable color change from red to yellow-green, which could be conveniently readout in solution even by the naked eye. Since the bioconjugations used as the aptasensor can be produced at large scale, this method can be used for in situ, rapid, or high-throughput OTA detection after only an incubation step in a homogeneous mode. We believe that this novel aptasensing strategy provides not only a promising method for OTA detection but also a universal model for detecting diverse targets by changing the corresponding aptamer.

Silver nanoparticles (NPs) decorated nitrogen doped graphene (NG) nanocomposites were prepared through a one-step thermal-treatment route using arginine as the nitrogen source. By integrating the excellent electrical properties and large surface area of Ag NPs and NG, the obtained Ag/NG nanocomposites show more effective electron transfer and high loading capacity than Ag–graphene and pure NG. In the presence of a target, the stronger interaction between the aptamer and the target promotes the formation of a target–aptamer complex on the electrode surface which blocks the electron transfer. Based on this sensing mechanism, a novel and highly sensitive biosensing platform by the use of Ag/NG as enhancing materials is demonstrated for detection of the model target, acetamiprid. The presented aptasensor exhibited a wide linear response for acetamiprid in the range of 1 × 10−13 M to 5 × 10−9 M with a low detection limit of 3.3 × 10−14 M (S/N = 3). Moreover, this electrochemical aptasensor avoided complicated labeling procedures and showed magnificent sensitivity, high selectivity and low cost, which made it not only convenient but also time-saving and applicable. Furthermore, the proposed design may offer a promising way to develop a new electrochemical aptasensor for sensitive and specific detection of a wide spectrum of analytes in food, medical and environmental fields.

Nitrogen-doped graphene quantum dots (NGQDs), as a new class of quantum dots, have potential applications in fuel cells and optoelectronics fields due to their electrocatalytic activity, tunable luminescence and biocompatibility. Herein, a facile hydrothermal approach for cutting nitrogen-doped graphene into NGQDs has been proposed for the first time. The resulting NGQDs were homogeneously modified onto the surface of graphene oxide (GO) to form NGQDs-GO nanocomposites. Compared with NGQDs, the as-prepared NGQDs-GO nanocomposites exhibited excellent electrochemiluminescence (ECL) performances including 3.8-fold enhancement of ECL intensity and a decrease by 200 mV of the ECL onset potential, which are ascribed to the introduction of GO. Based on the selective inhibitory effect of pentachlorophenol (PCP) on the ECL intensity of the NGQDs-GO system, a novel ECL sensor for PCP concentration determination was constructed, with a wide linear response ranging from 0.1 to 10 pg mL−1 and a detection limit of 0.03 pg mL−1. The practicability of the sensing platform in real water samples showed satisfactory results, which could open the possibility of using NGQDs-based nanocomposites in the electroanalytical field.

•MWCNTs@graphene oxide nanoribbons show ~6-fold enhanced oxidation current of luminol.•MWCNTs@graphene oxide nanoribbons show ~5.3-fold amplified ECL intensity of luminol.•A “signal on” ECL sensor for sensitive detection of PCP was constructed.•The resulting ECL sensor exhibits good performances for PCP detection.A “signal on” electrochemiluminescence (ECL) sensor for pentachlorophenol (PCP) detection was constructed based on the amplified ECL of luminol at a multiwalled carbon nanotubes@graphene oxide nanoribbons (MWCNTs@GONRs) modified electrode. Due to the good electrocatalytic activity of MWCNTs@GONRs toward luminol system, the oxidation peak current of luminol at the MWCNTs@GONRs modified electrode was enhanced for ~6-fold than that of the bare electrode; and the ECL intensity of luminol was amplified for ~5.3-fold correspondingly. Furthermore, the amplified ECL signal of luminol was linear with the concentration of PCP in the range between 2 pg mL−1 and 10 ng mL−1 with a detection limit of 0.7 pg mL−1 (S/N=3). With the merits of good reproducibility, acceptable stability, wide linear range, low detection limit and simplicity, the proposed luminol ECL sensor showed great potential in the field of analytical applications.

•The electrochemical and ECL performance between Ag/N–G and Ag/graphene is compared.•Ag/N–G display enhanced electrochemical activity to K2S2O8 compared with Ag/graphene.•Ag/N–G show amplified ECL intensity and decreased onset potential in K2S2O8 solution.•Lower detection limit and wider linear range toward PCP is obtained at Ag/N–G/GCE.This communication clearly highlights the importance and necessity for a comparison investigation between nitrogen-doped graphene (N–G) and graphene as a two-dimensional mat of metal nanoparticles (NPs). We presented Ag NPs as a model of metal NPs for fabricating Ag/N–G and Ag/graphene nanocomposites, respectively. Compared with Ag/graphene nanocomposites, the Ag/N–G nanocomposites could facilitate the electrochemical redox process of S2O82−, and showed improved electrochemiluminescence (ECL) performances including increasing ~2.25-fold ECL intensity and decreasing ~330 mV onset potential of S2O82−, respectively. Further, the as-prepared pentachlorophenol ECL sensor based on Ag/N–G nanocomposites showed a wider linear range and lower detection limit than those of the Ag/graphene nanocomposites. This study could be potentially useful for understanding the role of N–G in electrochemistry, and opening a new aspect for exploring and developing potential application of N–G based materials in electrocatalysis and sensing fields.

•A ratiometric fluorescence probe has been prepared with desired intensity ratio.•The sensing system displays distinguishable color changes from red to green.•The Cys and Hcy content can be easily determined by the naked eye.•The sensing scheme can be fully integrated in a filter paper-based assay.•The proposal can serve as a sensing basis for the point-of-care application.Simple, inexpensive, portable sensing strategies for those clinically relevant molecules have attained a significant positive impact on the health care system. Herein, we have prepared a dual-emission ratiometric fluorescence probe with desired intensity ratio and demonstrated its efficiency for onsite naked eye determination of cysteine (Cys) and homocysteine (Hcy). The hybrid probe has been designed by hybridizing two differently sized CdTe quantum dots (QDs), in which the red-emitting CdTe QDs (rQDs) entrapped in the silica sphere acting as the reference signal, and the green-emitting CdTe QDs (gQDs) covalently attached on the silica surface serving as the response signal. When 1,10-phenanthroline with strong coordination ability to Cd atoms in gQDs was introduced, the fluorescence of the gQDs was effectively quenched, while the fluorescence of the rQDs stayed constant. Upon exposure to different contents of Cys or Hcy, the fluorescence of gQDs can be recovered gradually due to the displacement of the quencher. Based on the background signal of rQDs, the variations of the sensing system display continuous fluorescence color changes from red to green, which can be easily observed by the naked eye. The assay requires ∼20 min and has a detection limit of 2.5 and 1.7 μM for Cys and Hcy, respectively. Furthermore, we demonstrate that this sensing scheme can be fully integrated in a filter paper-based assay, thus enabling a potential point-of-care application featuring easy operation, low power consumption, and low fabrication costs.

•A facile aptasensor has been developed for the colorimetric detection of acetamiprid.•Aptamer without any chemical modifications is employed as the recognition element.•The acetamiprid content can be judged by the naked eyes or the UV–vis spectrometer.•The sensor has a lower detection limit than that of the reported (HP)LC method.•This work provides a universal strategy for aptamer-based colorimetric biosensor.A facile aptasensor has been developed for the colorimetric detection of acetamiprid by using the hemin-functionalized reduced graphene oxide (hemin-rGO) composites. The as-prepared hemin-rGO composites possessed both the ability of rGO to physically adsorb the aptamers and the peroxidase-like activity of hemin that could catalyse 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, to produce a solution with blue color. The well-dispersed hemin-rGO composites coagulated completely at the proper salt concentration; however, the coagulation of hemin-rGO was vanished when abundant aptamers were adsorbed on its surface because the attached negatively charged DNA backbone increased individual hemin-rGO electrostatic repulsion. In the detection scheme, acetamiprid with different concentrations was firstly incubated with the same amount of aptamer. The more acetamiprid in the tested solution, the less free aptamers were absorbed on the hemin-rGO surface, making the composites coagulate to a higher degree in the presence of the optimum NaCl concentration. As a consequence, the content of hemin-rGO in the supernatant was decreased after centrifugation, which catalysed oxidation of TMB in the presence of H2O2 to produce light blue color with a low absorbance. The color variation relavant to the acetamiprid concentration can be judged by the naked eyes and easily monitored by the inexpensive UV–vis spectrometer. Such designed aptasensor displayed a linear response for acetamiprid in the range from 100 nM to 10 μM with a detection limit of 40 nM (S/N=3). This colorimetric aptasensing platform offers great advantages including the simple operation process, low-cost portable instrument, and user-friendly applications.

•AuNPs–rGO was fabricated to provide vast binding sites for DNA strands.•A sandwich aptasensor was designed with AuNPs–rGO as signal amplification platform.•7∼ orders of magnitude in Rct was obtained compared with the AuNPs–rGO absence one.•The impedimetric aptasensor could detect OTA with picomolar sensitivity.•The sensitivity is 200∼ fold lower than that of most existed aptasensors using EIS.An amplified electrochemical impedimetric aptasensor for ochratoxin A (OTA) was developed with picomolar sensitivity. A facile route to fabricate gold nanoparticles covalently bound reduced graphene oxide (AuNPs–rGO) resulted in a large number of well-dispersed AuNPs on graphene sheets with tremendous binding sites for DNA, since the single rGO sheet and each AuNP can be loaded with hundreds of DNA strands. An aptasensor with sandwich model was fabricated which involved thiolated capture DNA immobilized on a gold electrode to capture the aptamer, then the sensing interface was incubated with OTA at a desired concentration, followed by AuNPs–rGO functionalized reporter DNA hybridized with the residual aptamers. By exploiting the AuNPs–rGO as an excellent signal amplified platform, a single hybridization event between aptamer and reporter DNA was translated into more than 107 redox events, leading to a substantial increase in charge-transfer resistance (Rct) by 7∼ orders of magnitude compared with that of the free aptamer modified electrode. Such designed aptasensor showed a decreased response of Rct to the increase of OTA concentrations over a wide range of 1 pg mL−1–50 ng mL−1 and could detect extremely low OTA concentration, namely, 0.3 pg mL−1 or 0.74 pM, which was much lower than that of most other existed impedimetric aptasensors. The signal amplification platform presented here would provide a promising model for the aptamer-based detection with a direct impedimetric method.

Beta-nickel hydroxide nanowires/reduced graphene oxide (RGO) composites are fabricated by a one-step reactable ionic liquid-assisted hydrothermal method, using the versatile 1-butyl-3-methylimidazolium trifluoroacetate as templates, co-solvents and reactants. The results show that β-Ni(OH)2 nanowires are well dispersed on the surface of reduced graphene oxide sheets, and the as-prepared β-Ni(OH)2 nanowires/RGO composite exhibits a huge BET surface area of 216.99 m2 g−1 with a pore volume of 0.34 m3 g−1. Furthermore, β-Ni(OH)2 nanowires/RGO composite as an electrode material for supercapacitors displays high specific capacitance, good cycling stability and coulombic efficiency. An extremely high specific capacitance of ∼1875 F g−1 can be obtained at 1 A g−1 in 6 M KOH aqueous solution, and retains 98.3% of its original capacity after 1000 charge-discharge cycles at 8 A g−1. The resulting composite is a promising candidate as an electrode material for extensive applications in energy storage systems.

Porous hierarchical broom-like and rod-like Co3O4 nanostructures have been successfully prepared in the presence of a reactable ionic liquid 1-hexadecyl-3-methylimidazolium trifluoroacetate [C16mim]CF3COO by a hydrothermal method in combination with calcination of Co(CO3)0.5(OH)·0.11H2O precursors. During the reaction process, the ionic liquid [C16mim]CF3COO performed three roles: as the reactant, template and co-solvent. A possible formation mechanism of the structures was proposed on the basis of the experimental results. After the thermal decomposition treatment of the precursors, the as-obtained porous Co3O4 samples well retain the hierarchical broom-like and rod-like nanostructures. Subsequently, they are applied as the electrode materials for supercapacitors. The electrochemical experiments reveal that the porous hierarchical broom-like Co3O4 nanostructures exhibit a higher capacitance (722.2 F g−1 at 1 A g−1) compared to the porous rod-like Co3O4 nanostructures (191.2 F g−1 at 1 A g−1).

A novel visible light photoelectrochemical (PEC) platform coupled with enzyme-inhibition for rapid and sensitive determination of organophosphates (OPs) was constructed based on a dual-functional Cd0.5Zn0.5S-reduced graphene oxide (Cd0.5Zn0.5S-rGO) nanocomposite. Due to the inherent biocompatibility of the Cd0.5Zn0.5S-rGO nanocomposite, acetylcholinesterase (AChE) immobilized on the Cd0.5Zn0.5S-rGO modified electrode can hydrolyze acetylthiocholine chloride into thiocholine, which could increase the photocurrent of the enzyme electrode, and the further inhibition of OPs on the enzyme electrode could decrease the photocurrent response. Based on the notable change in the PEC response of the AChE–Cd0.5Zn0.5S-rGO modified electrode and using Dursban as a model, a simple and effective way for PEC monitoring of OPs is proposed, which showed a wide linear range of 0.001–1 μg mL−1 with a low detection limit of 0.3 ng mL−1 (S/N = 3). Moreover, the biosensor was successfully challenged with water samples, demonstrating a new method for rapid and sensitive screening/evaluating exposure to organophosphorus pesticides and other hazardous substances.

•A novel sensor for nitenpyram based on Cu NPs/N-G is proposed.•High sensitivity benefits from the synergistic effect of Cu NPs and N-G.•Cu NPs/N-G show better electrochemical activity than Cu NPs and N-G for nitenpyram.•A broad linear range and low detection limit for nitenpyram detection is obtained.In this work, a novel electrochemical sensing platform has been designed for sensitive determination of nitenpyram on the basis of copper nanoparticles functionalized nitrogen-doped graphene (Cu NPs/N-G) nanocomposites. The Cu NPs/N-G nanocomposites have exhibited high electrocatalytic activity and satisfactory response toward the oxidation of nitenpyram in Britton–Robinson solution, attributing to the synergistic effect of Cu NPs and N-G. The resulting sensor exhibited high sensitivity of 1011 μA mM−1 cm−2 for nitenpyram detection with a wide linear range from 5 μM to 1.11 mM as well as low detection limit of 2.0 μM at signal-to-noise of 3. Moreover, the Cu NPs/N-G nanocomposites showed excellent selectivity and remarkable stability for the oxidation of nitenpyram. The proposed sensor has been successfully applied to the determination of nitenpyram in river water samples with satisfactory results. This can take new opportunities for fast, simple and selective detection of nitenpyram and provide a promising platform for sensor designs for nitenpyram detection.

Hierarchical mesoporous Co3O4 bundles were obtained by a hydrothermal method combined with a subsequent calcination treatment. During the synthesis of the precursor Co2(OH)2CO3, the versatile ionic liquid 1-butyl-3-methylimidazolium trifluoroacetate performed three roles as the co-solvent, precursor, and template. A supercapacitor based on the as-prepared Co3O4 was fabricated and further evaluated by cyclic voltammetry and chronopotentiometry measurements, which exhibited a specific capacitance of 357 F g−1 at 2 A g−1 after 500 cycles under high loading conditions (approximately 8 mg cm−2). Moreover, the mesoporous Co3O4 was found to maintain 85.5 % specific capacitance with an increase in the current density from 1 to 20 A g−1; this behavior was attributed to the unique structure of the bundles which allowed most of the Co3O4 sheets to efficiently participate in the electrochemical reaction.

•Polyoxometalate@mrGO was used as the versatile immobilization matrix for Ru(bpy)32+.•The resulting hybrids were surface-confined simply involved using magnetic electrode.•This magneto-controlled ECL sensor showed stable and large response to NADH.•The sensing platform provide new strategy for dehydrogenase-based ECL biosensors.We demonstrated here the exploration of polyoxometalate (POM) coated magnetic Fe3O4/reduced graphene oxide (POM@mrGO) composite as the versatile immobilization matrix for the electrochemiluminescence (ECL) agent Ru(bpy)32+. The effective modification of Ru(bpy)32+/POM@mrGO hybrid simply involved using magnetic electrode showed 10-fold ECL intensity increase than that observed for Ru(bpy)32+/Nafion@mrGO to the same concentration of nicotinamide adenine dinucleotide (NADH), which is largely due to POM׳s good electrocatalytic activity towards NADH oxidation. These findings allowed the stable and ultrasensitive ECL detection of NADH as low as 0.1 nM. The good stability and high sensitivity of the magneto-controlled ECL sensor enabled us to explore the feasibility of applying the sensing platform to fabricating the ECL biosensors in which the NADH was produced from the dehydrogenase-based enzymatic reaction in the presence of NAD+ cofactor. With l-lactate dehydrogenase as a model, a l-lactate biosensor was successfully constructed where we showed that the ECL intensity of the biosensor increased with the increasing l-lactate concentration. Excellent performance of the presented biosensor has been achieved including a wide linear range extended from 5.0×10−9 M to 5.0×10−4 M and an extremely low detection limit of 0.4 nM. Such sensing strategy combines enzymatic selectivity with simple sensor preparation can be used as a new and biocompatible platform for dehydrogenase-based ECL biosensing.

•Copper nanoparticles decorated nitrogen-doped graphene (Cu–N-G) was synthesized by a facile thermal treatment.•Due to the integration of nitrogen-doped graphene, the Cu–N-G exhibited the oxidation peak current of glucose ca. 23-fold higher than that of pure Cu nanoparticles.•The proposed sensor showed excellent performances including wide linear range of 0.004–4.5 mM, high sensitivity of 48.13 μA mM−1, etc.Copper nanoparticles (NPs) decorated nitrogen-doped graphene (Cu–N-G) was prepared by a facile thermal treatment, and further employed as a novel sensing material for fabricating the sensitive non-enzymatic glucose sensor. Compared with pure Cu NPs, the Cu–N-G showed enhanced electrocatalytic activity to glucose oxidation due to the integration of N-G, which exhibited the oxidation peak current of glucose ca. 23-fold higher than that of pure Cu NPs. The presented sensor showed excellent performances for glucose detection including wide linear range of 0.004–4.5 mM, low detection limit (1.3 μM, S/N=3), high sensitivity (48.13 μA mM−1), fast response time (<5 s), good selectivity to the general coexisted interferences, etc. Such properties would promote the potential application of the nitrogen-doped graphene as enhanced materials in fabricating sensors for chemical and biochemical analysis.

This work reports a novel strategy to amplify the electrochemiluminescence (ECL) signal of peroxydisulfate solution based on the Au nanoparticle decorated reduced graphene oxide (Au NP–RGO), and further an ECL biosensor for sensitive and selective detection of dopamine (DA) was constructed. Due to the synergistic amplification of Au NPs and RGO, the ECL signal of peroxydisulfate solution on the Au NP–RGO modified electrode was about 5-fold enhanced compared to that of the bare electrode with the ECL onset potential positively shifted from −1.2 V to −0.9 V. More interestingly, the ECL intensity of peroxydisulfate solution increased with the increase of DA concentration, based on which an ECL biosensor for DA determination was fabricated. The as-prepared solid-state ECL DA sensor showed a wide linear response of 0.02–40 μM with a detection limit of 6.7 nM (S/N = 3). Moreover, we expect this work would open up a new field in the application of peroxydisulfate solution ECL for highly sensitive bioassays.

A series of CdxZn1−xS–reduced graphene oxide (CdxZn1−xS–rGO) nanocomposites were successfully prepared by a facile one-pot reaction. In this reaction system, H2S gas acted as a sulfide source as well as a reducing agent, resulting in the formation of CdxZn1−xS nanoparticles and simultaneous reduction of graphene oxide sheets to rGO. The photoelectrochemical (PEC) performances of CdxZn1−xS–rGO nanocomposites were further investigated under visible irradiation, which showed that the photocurrent intensities were influenced by the cationic composition (x) in CdxZn1−xS–rGO nanocomposites. Compared with other CdxZn1−xS–rGO nanocomposites, the Cd0.5Zn0.5S–rGO nanocomposite displayed optimal photocurrent intensity, which was 5 times greater than that of CdS NPs. Based on Cu2+ selective suppression of the photocurrent intensity of the Cd0.5Zn0.5S–rGO nanocomposite, the photocurrent suppression obtained was linearly proportional to the logarithm of the concentration of Cu2+. The resulting Cu2+ photoelectrochemical sensor showed good performance including a wide linear range of 0.02 μM to 20 μM, low detection limit of 6.7 × 10−9 M (S/N = 3) and good anti-interference ability.

Multifunctional magnetic nanocomposites, iron (II) phthalocyanine@Fe3O4/reduced graphene oxide (FePc@Fe3O4/rGO), have been fabricated by a facile equilibrium adsorption process with Fe3O4/rGO nanocomposites as adsorbents. Based on their multifunctionality including magnetic and biomimetic catalytic properties, the as-prepared nanocomposites were further immobilized on the magnetic electrode surface by a fast and simple magnetism-assisted assembly for the reduction of tert-butyl hydroperoxide (TBHP). The proposed biomimetic sensor can be applied to the quantification of TBHP with a linear range over the concentration range of 20 μM–60 mM and a detection limit of 7.5 μM (S/N = 3), which offers several advantages including easy preparation, good sensitivity, long-term stability, and low cost.Graphical abstractHighlights► Multifunctional FePc@Fe3O4/rGO was fabricated by a facile equilibrium adsorption. ► The nanocomposites were modified on electrode by a fast magnetism-assisted assembly. ► The immobilized nanocomposites were used as biomimetic catalysts for TBHP reduction. ► This biomimetic sensor offers a wide linear range for TBHP determination. ► The advantages of the sensor include easy preparation, high stability, and low cost.

•The Fe3O4-GNRs were prepared in a facile one-step solvothermal process.•The electrochemical activities of Fe3O4-GNRs and Fe3O4-G were compared.•Fe3O4-GNRs show better electrochemical activity than Fe3O4-G for dopamine oxidation.•It is useful for understanding the structure/property relation of carbon materials.Fe3O4-functionalized graphene nanoribbons (Fe3O4-GNRs) were prepared in situ by a facile one-step solvothermal process. The as-prepared nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, etc., and the results indicate that the Fe3O4 nanoparticles were successfully formed on the GNRs. Furthermore, the electrochemical activity of Fe3O4-GNRs and Fe3O4-functionalized graphene nanosheets (Fe3O4-G) was compared by employing dopamine as the redox probe, which indicated that the redox process of the probe at Fe3O4-GNRs is faster than that at the Fe3O4-G modified electrode. This study could be potentially useful for understanding the structure/property relationship of the graphene-based materials, and synthesizing advanced graphene-based materials for electrochemical applications.

Fe3O4 nanoparticles-decorated reduced graphene oxide magnetic nanocomposites (Fe3O4/rGO NCs) were prepared by a facile one-step strategy, and further used as heterogeneous Fenton-like catalysts for catalytic wet hydrogen peroxide oxidation (CWHPO) of methylene blue (MB) at 25 °C and atmospheric pressure. The effects of variables such as the Fe3O4/rGO with the mass ratio of rGO, initial pH, MB concentration and H2O2 dosage were investigated. The Fe3O4/rGO NCs with rGO mass ratio of 10.0 wt % showed the highest H2O2-activating ability, which was six-fold than that of pure Fe3O4 nanoparticles (NPs). The resulting catalysts demonstrated high catalytic activity in a broad operation pH range from 5 to 9, and still retained 90.5 % catalytic activity after reuse in five cycles. Taking advantage of the combined benefits of rGO and magnetic Fe3O4 NPs, these Fe3O4/rGO NCs were confirmed as an efficient heterogeneous Fenton-like catalyst for CWHPO to treat organic pollutants. And a reasonable catalytic mechanism of Fe3O4/rGO NCs was proposed to interpret the degradation process.

This work reports a rapid and sensitive organophosphates (OPs) amperometric biosensor based on acetylcholinesterase (AChE) immobilized on CdS–decorated graphene (CdS–G) nanocomposite. The as-prepared biosensor shows high affinity to acetylthiocholine (ATCl) with a Michaelis–Menten constant (Km) value of 0.24 mM. A rapid inhibition time (2 min) is obtained due to the integration of the CdS–G nanocomposite. Based on the inhibition of OPs on the enzymatic activity of the immobilized AChE, and used carbaryl as the model compound, the resulting biosensor exhibits excellent performance for OPs detection including good reproducibility, acceptable stability, and a reliable linear relationship between the inhibition and log[carbaryl] from 2 ng mL−1 up to 2 μg mL−1 with a detection limit of 0.7 ng mL−1, which provides a new promising tool for analysis of enzyme inhibitors.Graphical abstractHighlights► Based on acetylcholinesterase immobilized on CdS–decorated graphene (CdS–G) nanocomposite, a rapid and sensitive organophosphates amperometric biosensor was constructed. ► The as-prepared biosensor showed high affinity to acetylthiocholine with a Michaelis–Menten constant value of 0.24 mM. ► A rapid inhibition time was obtained due to the integration of the CdS–G nanocomposite. ► The resulting biosensor exhibited a reliable linear relationship between the inhibition and log[carbaryl] from 2 ng mL−1 up to 2 μg mL−1.

We report a novel and facile electrodeposition method to fabricate a nano-structure film of the unsubstituted metal phthalocyanine on a glassy carbon electrode (GCE). In this electrodeposition system, unsubstituted iron(II) phthalocyanine (u-FePc) was chosen as the model complex of the unsubstituted metalphthalocyanine, and the ionic liquid 1-octyl-3-methylimidazolium trifluoroacetate was employed as the solvent and electrolyte, thus avoiding the use of additional costly supporting electrolyte. Excellent electrocatalytic performance of the u-FePc nano-structure film was first evaluated by electrocatalytic oxidation of ascorbic acid (AA). Compared with the bare GCE, the oxidation peak potential of AA at u-FePc/GCE shifted negatively about 264 mV, and the oxidation peak current increased about 1.8 times. Furthermore, the as-prepared film was employed for the investigation of luminol electrochemiluminescence (ECL) behavior in neutral solution, which showed excellent performance including under selected experimental conditions, the ECL intensity showing an acceptable linear relationship for luminol concentrations between 5 × 10−8 and 5 × 10−6 M, and a linear response to H2O2 over a wide concentration range, from 1.0 × 10−8 to 1.0 × 10−5 M in 3.0 μM luminol solution.

This work describes a highly sensitive and rapid amperometric biosensor for organophosphate compounds (OPs) based on immobilization of acetylcholinesterase (AChE) on a novel TiO2-decorated graphene (TiO2-G) nanohybrid, which was constructed by in situgrowth of TiO2 nanoparticles (NPs) on the graphene sheet. The well-dispersed TiO2 NPs eliminated the restacking of TiO2-G nanohybrids. Due to the integrating of TiO2-G nanohybrids, the as-prepared biosensor showed high affinity to acetylthiocholine (ATCl) with a Michaelis–Menten constant (Km) value of 0.22 mM, and rapid inhibition time (3 min). Further, based on the inhibition of OPs on the enzymatic activity of the immobilized AChE, and using carbaryl as a model compound, the inhibition of carbaryl was proportional to its concentration ranging from 0.001 to 0.015 and 0.015 to 2 μg mL−1 with a detection limit of 0.3 ng mL−1 (S/N = 3). The developed biosensor exhibited a good performance for organophosphate pesticide detection, including good reproducibility and acceptable stability, which provided a new and promising tool for the analysis of enzyme inhibitors.

Integrating graphene-based composites with enzyme provides a potent strategy to enhance biosensor performance due to their unique physicochemical properties. Herein we report on the utilization of graphene–CdS (G–CdS) nanocomposite as a novel immobilization matrix for the enzymes, which glucose oxidase (GOD) was chosen as model enzyme. In comparison with the graphene sheet and CdS nanocrystal, G–CdS nanocomposite exhibited excellent electron transfer properties for GOD with the rate constant (ks) of 5.9 s−1 due to the synergy effect of graphene sheet and CdS nanocrystals. Further, based on the decrease of the electrocatalytic response of the reduced form of GOD to dissolved oxygen, the obtained glucose biosensor displays satisfactory analytical performance over an acceptable linear range from 2.0 to 16 mM with a detection limit of 0.7 mM, and also prevents the effects of interfering species, which is suitable for glucose determination by real samples. These results mean that this immobilization matrix not only can be used for immobilizing GOD, but also can be extended to other enzymes and bioactive molecules, thus providing a promising platform for the development of biosensors.

Graphene-CdS (G-CdS) nanocomposites were successfully prepared by CdS nanocrystals (CdS NCs) formed in situ on the surface of graphene sheets, using graphene oxide (GO) sheets with rich negatively charged carboxylic acid groups as starting materials. Compared with pure CdS NCs, the presence of the graphene doped in G-CdS nanocomposites could facilitate the electrochemical redox process of CdS NCs; further, the as-prepared G-CdS nanocomposite can react with H2O2 to generate strong and stable electrochemiluminescent (ECL) emission, which not only enhances its ECL intensity by about 4.3-fold but also decreases its onset potential for about 320 mV. The as-prepared solid-state ECL H2O2 sensor shows acceptable linear response from 5 μM up to 1 mM with a detection limit of 1.7 μM (S/N = 3). The ECL H2O2 sensor exhibits excellent reproducibility and long-term stability. Such a property would promote the potential application of the graphene as enhanced materials in fabricating sensors for chemical and biochemical analysis.

•Au nanrods were designed to modify α-Fe2O3-NG to form a ternary hybrid.•The Au nanrods SPR-enhanced PEC aptasensing of E2 was proposed.•The PEC aptasensing exhibited ultrasensitivity toward E2.•The proposed method was used to detect E2 in milk powder samples.It remains a vital task to establish ultrasensitive sensing interfaces for detection of target analytes to meet the demands of modern analysis. Herein, a highly sensitive turn-on photoelectrochemical (PEC) platform for trace 17β-estradiol (E2) assay was developed based on Au nanrods (AuNRs) with surface plasmon resonance (SPR) properties induced signal amplification. Specifically, a ternary hybrid was prepared by integrating hematite (α-Fe2O3) nanocrystals and N-doped graphene (NG) with AuNRs, which further served as highly efficient photoactive species. Subsequently, a PEC sensing platform was fabricated based on the specific binding of E2 and its aptamer. On such a sensor, the capture of E2 molecules by aptamers led to increased photocurrent. This was attributed to that the specific recognition reaction between E2 and aptamer resulted in the conformational change of the aptamers and complete dissociation of some aptamers on the PEC sensing interface. It can be confirmed by the electrochemical impedance spectroscopy (EIS) results. This process decreased the steric hindrances between the electrode surface and solution and thus increased the photocurrent response. Under the optimal conditions, the as-prepared PEC aptasensor exhibited superb analytical performances for detection of E2 in the range from 1×10−15 M to 1×10−9 M with a detection limit of 3.3×10−16 M. The aptasensor manifested outstanding selectivity towards E2 when other endocrine disrupting compounds with similar structure coexisted. Furthermore, the aptasensor was successfully applied for the determination of E2 in milk powder. The present strategy provides a potential way to boost the activity of photoactive materials and improve the sensitivity of PEC biosensor.

•Fluorescence “On-Off-On” process between multicolor QDs and MWCNTs@GONRs was achieved.•FRET between multicolor QDs and MWCNTs@GONRs was employed for dual target DNAs monitoring.•Simultaneous analysis of promoter cauliflower mosaic virus 35 s and terminator nopaline synthase.•The method possesses the advantages of feasibility and reliability.With the increasing concern of potential health and environmental risk, it is essential to develop reliable methods for transgenic soybean detection. Herein, a simple, sensitive and selective assay was constructed based on homogeneous fluorescence resonance energy transfer (FRET) between CdTe quantum dots (QDs) and multiwalled carbon nanotubes@graphene oxide nanoribbons (MWCNTs@GONRs) to form the fluorescent “on-off-on” switching for simultaneous monitoring dual target DNAs of promoter cauliflower mosaic virus 35 s (P35s) and terminator nopaline synthase (TNOS) from transgenic soybean. The capture DNAs were immobilized with corresponding QDs to obtain strong fluorescent signals (turning on). The strong π–π stacking interaction between single-stranded DNA (ssDNA) probes and MWCNTs@GONRs led to minimal background fluorescence due to the FRET process (turning off). The targets of P35s and TNOS were recognized by dual fluorescent probes to form double-stranded DNA (dsDNA) through the specific hybridization between target DNAs and ssDNA probes. And the dsDNA were released from the surface of MWCNTs@GONRs, which leaded the dual fluorescent probes to generate the strong fluorescent emissions (turning on). Therefore, this proposed homogeneous assay can be achieved to detect P35s and TNOS simultaneously by monitoring the relevant fluorescent emissions. Moreover, this assay can distinguish complementary and mismatched nucleic acid sequences with high sensitivity. The constructed approach has the potential to be a tool for daily detection of genetically modified organism with the merits of feasibility and reliability.

•Easily synthesized graphitic carbon nitride quantum dots (g-CNQDs) were explored to serve as a sensitizer to improve the photoelectrochemical property of Bi2MoO6 NCs.•G-CNQDs in situ coupling to Bi2MoO6 nanohybrids were obtained via a facile and simple solvothermal method.•The as-prepared nanohybrids displayed enhanced photocurrent intensity under visible light irradiation because of the effective separation of photoinduced electrons and holes.•A novel PEC sensor for the detection of Cu2 + was designed.Graphitic carbon nitride (g-C3N4) based nanohybrids have drawn considerable attentions due to superior performances. However, the photoactivity of bulk g-C3N4 is limited due to the recombination of its photogenerated electron-hole pairs. Graphitic carbon nitride quantum dots (g-CNQDs), as a newly developed semiconductor, are easily prepared and possess good stability, water-solubility and electronic properties. In this work, we explored the fabrication of nanohybrids by in situ coupling of g-CNQDs and Bi2MoO6 nanoparticles (NPs). The as-prepared nanohybrids displayed nearly 3-fold and 6-fold enhanced photocurrent intensity than pure g-CNQDs and Bi2MoO6 NPs. This improvement was attributed to the accelerated charge transfer from the conduction band of g-CNQDs to that of Bi2MoO6. Based on the excellent photoelectrochemical (PEC) performances, the nanohybrids were successfully applied in the construction of Cu2 + PEC sensor. Under optimal conditions, the resulting sensor showed good performances with a wide linear range from 3 nM to 40 μM and a good selectivity, which indicated that g-CNQDs/Bi2MoO6 nanohybrids could serve as a promising photoactive material for PEC sensing.

In this paper, the photoelectrochemical behavior of graphene-TiO2 (G-TiO2) nanohybrids was investigated in the visible region and a new photoelectrochemical sensor for sensitive determination of nicotinamide adenine dinucleotide (NADH) was proposed. Under visible light, the G-TiO2 nanohybrids possessed enhanced photocurrent, which was nearly 5 times than that of pure TiO2 nanocrystals (NCs). Based on the enhanced photocurrent of G-TiO2 nanohybrids toward NADH, a new photoelectrochemical methodology for ultrasensitive determination of NADH was developed. The proposed sensor showed linearly enhanced photocurrent by increasing the NADH concentration from 1.0 × 10−8 to 2.0 × 10−3 M with a low detection limit of 3.0 × 10−9 M. Furthermore, this sensor exhibited good selectivity and stability towards NADH determination. This strategy opens up a new avenue for the application of graphene-based hybrids in the field of photoelectrochemical sensing and monitoring.Graphical abstractDownload full-size imageHighlights► The photoelectrochemical behavior of G-TiO2/GCE was investigated in visible region. ► The G-TiO2/GCE possessed enhanced photocurrent than pure TiO2 nanocrystals. ► A photoelectrochemical sensor for ultrasensitive determination of NADH was proposed. ► The proposed sensor showed linear range of 1.0 × 10−8 to 2.0 × 10−3 M for NADH detection. ► This strategy largely reduces the destructive effect of UV light to biomolecules.

Considering that ultraviolet light may cause the denaturation of biomaterials, searching for and engineering innovative and advanced nanomaterials with excellent photoelectrochemical properties under visible light illumination are of great significance in the fundamental understanding and application of photoelectrochemical (PEC) sensors. As a widely applied visible light response material, the applications of Bi2WO6 in PEC fields were restricted because of the rapid recombination of photoinduced electron–hole pairs. In this work, Bi2WO6 functionalized reduced oxide (Bi2WO6–rGO) nanocomposites (NCs) were prepared by a one-step solvothermal method. After optimizing the content of rGO, the Bi2WO6–rGO2.94% NCs displayed enhanced photocurrent intensity (the starting mass ratios of GO to Bi2WO6 = 0.0294), which was nearly 2.7-fold compared to that of pure Bi2WO6 nanoparticles because of the separation of the photoinduced carriers and the enhancement of visible light absorption. Based on the coupling of Pb2+-induced allosteric transition of G-quadruplex DNAzyme and the enzymatic biocatalytic precipitation (BCP), Bi2WO6–rGO2.94% NCs were applied in the construction of a novel PEC sensor for the determination of Pb2+. The as-fabricated PEC sensor exhibited good anti-interference ability and a good linear relationship was obtained between the photocurrent intensity and the logarithm of the Pb2+ concentration over a concentration range from 0.01 to 50 μM and with a detection limit of 3.3 nM (S/N = 3), indicating that Bi2WO6–rGO NCs would be promising materials for PEC sensing.

A novel universal colorimetric sensor for simultaneous dual target detection through DNA-directed self-assembly of graphene oxide and magnetic separation has been designed for the first time.

AgBr nanoparticles anchored nitrogen-doped graphene nanocomposites were designed to obtain enhanced electrochemiluminescence intensity and better stability, and further applied in electrochemiluminescence detection for the first time.

Graphene quantum dots (GQDs), a type of emerging luminescent quantum dot, have drawn remarkable attention owing to their numerous fascinating properties and wide range of potential applications. Despite the intensive research efforts devoted to GQD fabrication, the mass production of high-quality GQDs in a reproducible and eco-friendly manner still represents a great challenge. Hence, we introduce an environmentally friendly, fast and industrially promising method for generating GQDs in large scale via the ionic liquid (IL)-assisted controllable electrochemical exfoliation of carbon fibers. Interestingly, it is found that the size-dependent optical properties of the as-prepared GQDs can be adjusted by using IL electrolytes with different water contents. For example, volume ratios of H2O/IL of 0%, 15% and 30% generate blue-emitting GQDs (B-GQDs), green-emitting GQDs (G-GQDs) and yellow-emitting GQDs (Y-GQDs), respectively. More interestingly, when pure IL is used as the electrolyte, IL-functionalized GQDs with blue photoluminescence emission (B-GQDs) are generated. These functionalized GQDs can effectively improve the electrochemiluminescence (ECL) performance of the system of Ru(bpy)32+–ECL. Furthermore, we have fabricated a well-designed ECL sensor with satisfactory sensitivity for the determination of pentachlorophenol (PCP). More importantly, this proposed green and large-scale approach provides a promising and extremely flexible platform for the preparation of GQDs with tunable photoluminescence.

In this work, hollow carbon nanospheres (HCNS) were prepared, followed by the introduction of gold nanoparticles (AuNPs) on the HCNS surface, and then functionalization with per-6-thio-β-cyclodextrin (CD) based on the formation of “Au–S” bond, resulting in a novel cyclodextrin/carbon-based nanohybrid (CD–AuNPs/HCNS), which possesses the unique properties of HCNS (excellent electrochemical properties and large surface area), CD (high host–guest recognition and water-solubility) and AuNPs (excellent electrocatalytic activity). The obtained CD–AuNPs/HCNS nanohybrids were characterized by scanning electron microscopy, transmission electron microscopy, inductively coupled plasma-atomic emission spectroscopy, Fourier transform infrared spectroscopy and electrochemical methods. Furthermore, CD–AuNPs/HCNS were applied in the simultaneous electrochemical sensing of o-dihydroxybenzene (o-DHB) and p-dihydroxybenzene (p-DHB) (both o- and p-DHB have similar structures and coexist in environment; moreover, they are toxic to humans and difficult to degrade). Under the optimum conditions, the detection limits of o- and p-DHB obtained in this work are 0.01 and 0.02 μM, respectively.

A novel ratiometric photoelectrochemical aptasensor based on the potentiometric resolved photocurrents generated from different PEC active materials was designed for the first time.

The design and exploitation of photoelectrochemical (PEC) sensors with advanced nanomaterials is of great importance to achieving the goal of sensitive and inexpensive detection. In this paper, a series of bismuth phosphate (BiPO4) functionalized reduced graphene oxide (BiPO4–rGO) nanocomposites (NCs) were prepared using a one-step solvothermal method. Compared with the pure BiPO4 nanoparticles (NPs), all of the as-prepared BiPO4–rGO NCs with different starting mass ratios of graphene oxide (GO) to BiPO4 showed an enhanced PEC response. On this basis, the BiPO4–rGO0.03 NCs (the starting mass ratio of GO to BiPO4 = 0.03) with the best PEC response were used for the PEC determination of chlorpyrifos. With the addition of chlorpyrifos, the formation of a Bi–chlorpyrifos complex on the BiPO4 NPs gave rise to an increase in steric hindrance which caused the electron transfer of BiPO4 NPs to trail off towards the electrode surface, and consequently resulted in an obvious decrease in photocurrent. The designed PEC sensor displayed a linear response for chlorpyrifos in the range from 0.05 to 80 ng mL−1 with a low detection limit of 0.02 ng mL−1 (S/N = 3). The common interferents such as methyl parathion, pentachlorophenol, and carbaryl had no obvious influence on the detection of chlorpyrifos, although these substances were reported to influence the PEC sensing of chlorpyrifos to some extent. The applicability of this method was also investigated by the determination of chlorpyrifos in wastewater samples with satisfactory results. Thus, it is expected that the resulting BiPO4–rGO NCs can serve as a potential photoactive material for PEC sensing related applications.

Electrochemiluminescence (ECL), a powerful analytical technique, was combined with the “ON1–OFF–ON2” strategy based on the chemical reactions and specific binding among different small chemical compounds for the highly sensitive assay of nonelectroactive organophosphate pesticides.

In this study, multiwalled carbon nanotube@reduced graphene oxide nanoribbon (MWCNT@rGONR) core–shell heterostructures have been synthesized by the facile unzipping of MWCNTs and subsequent chemical reduction with hydrazine. MWCNTs with diameter <10 nm were selected as the starting material to maintain narrow ribbons <30 nm wide with a few-layer structure. The most important discovery is that the resulting MWCNT@rGONR heterostructures possess intrinsic peroxidase-like activity, 15.9 times higher than that of MWCNTs and 8.4 times higher than that of their unreduced form. The nature of the peroxidase-like activity of the MWCNT@rGONR heterostructures can be attributed to the acceleration of their electron-transfer process and the consequent facilitation of ˙OH radical generation. Kinetic analysis demonstrates that the catalytic behavior is in accordance with typical Michaelis–Menten kinetics and the obtained kinetic parameters indicate that the MWCNT@rGONR heterostructures display a higher affinity for both H2O2 and 3,3,5,5-tetramethylbenzidine than that of horseradish peroxidase. On this basis, we have employed the MWCNT@rGONR heterostructures as novel biosensing platforms to develop a simple, sensitive, and selective colorimetric biosensor for free cholesterol determination. This work will facilitate the formation of MWCNT@rGONR heterostructures with narrow ribbons and the utilization of their intrinsic peroxidase-like activity in biotechnology and medical diagnostics.