By using in situ generation of electron acceptor coupled with heterojunction as dual signal amplification, a simple photoelectrochemical (PEC) bioanalysis platform was designed. The synergic effect between the photoelectrochemical (PEC) activities of carbon nitride (C3N4) nanosheets and PbS quantum dots (QDs) achieved almost nine-fold photocurrent intensity increment compared with the C3N4 alone. After the G-quadruplex/hemin/Pt nanoparticles (NPs) with catalase-like activity toward H2O2 were introduced, oxygen was in situ generated and acted as electron donor by improving charge separation efficiency and further enhancing photocurrent response. The dually amplified signal made enough sensitivity for monitoring H2O2 released from live cells. The photocathode was prepared by the stepwise assembly of C3N4 nanosheets and PbS QDs on indium tin oxide (ITO) electrode, which was characterized by scanning electron microscope. A signal-on protocol was achieved for H2O2 detection in vitro due to the relevance of photocurrent on the concentration of H2O2. Under the optimized condition, the fabricated PEC bioanalysis platform exhibited a linear range of 10–7000 μM with a detection limit of 1.05 μM at S/N of 3. Besides, the bioanalysis platform displayed good selectivity against other reductive biological species. By using HepG2 cells as a model, a dual signal amplifying PEC bioanalysis platform for monitoring cells was developed. The bioanalysis platform was successfully applied to the detection of H2O2 release from live cells, which provided a novel method for cells monitoring and would have prospect in clinical assay.Keywords: bioanalysis; cells monitoring; dual signal amplification; enzymatic catalysis; heterojunction; photoelectrochemical;

A universal and label-free photoelectrochemical cytosensing strategy was designed based on resonance energy transfer (RET) between carbon dots and cysteamine capped gold nanoparticles. RET promoted photo-to-current conversion efficiency and enhanced detection sensitivity. This proposed photoelectrochemical cytosensing platform exhibited a good performance for the assay of tumor cells with overexpressed receptors on cells.

A novel strategy for highly sensitive electrochemiluminescence (ECL) detection of DNA was proposed based on site-specific cleavage of BamHI endonuclease combined with the excellent ECL activity of graphene quantum dots (GQDs) and bidentate chelation of the dithiocarbamate DNA (DTC-DNA) probe assembly. The difference between photoluminescence and ECL spectral peaks suggested that a negligible defect existed on the GQDs surface for generation of an ECL signal. The formed DTC-DNA was directly attached to the gold surface by bidentate anchoring (S–Au–S bonds), which conferred a strong affinity between the ligands and the gold surface, increasing the robustness of DNA immobilization on the gold surface. BamHI endonuclease site-specifically recognized and cleaved the duplex symmetrical sequence, which made the double-stranded DNA fragments and GQDs break off from the electrode surface, inducing a decrease of the ECL signal. Using hepatitis C virus-1b genotype complementary DNA (HCV-1b cDNA) as a model, a novel signal-off ECL DNA biosensor was developed based on variation of the ECL intensity before and after digestion of the DNA hybrid. Electrochemical impedance spectroscopy confirmed the successful fabrication of the ECL DNA biosensor. This ECL biosensor for HCV-1b cDNA determination exhibited a linear range from 5 fM to 100 pM with a detection limit of 0.45 fM at a signal-to-noise ratio of 3 and showed satisfactory selectivity and good stability, which validated the feasibility of the designed strategy. The proposed strategy may be conveniently combined with other specific biological recognition events for expansion of the biosensing application, especially in clinical diagnoses.

A versatile photoelectrochemical biosensing platform was developed based on DNA–CdS quantum dots (QDs) sensitized single-walled carbon nanotubes (SWCNTs)-COOH. Combining with cyclic enzymatic amplification, a convenient, sensitive and specific biosensor for the direct detection of microRNAs (miRNAs) was designed, which provided a novel approach for analysis of miRNAs.

On the basis of the absorption and emission spectra overlap, an enhanced resonance energy transfer caused by excition-plasmon resonance between reduced graphene oxide (RGO)-Au nanoparticles (AuNPs) and CdTe quantum dots (QDs) was obtained. With the synergy of AuNPs and RGO as a planelike energy acceptor, it resulted in the enhancement of energy transfer between excited CdTe QDs and RGO-AuNPs nanocomposites. Upon the novel sandwichlike structure formed via DNA hybridization, the exciton produced in CdTe QDs was annihilated. A damped photocurrent was obtained, which was acted as the background signal for the development of a universal photoelectrochemical (PEC) platform. With the use of carcinoembryonic antigen (CEA) as a model which bonded to its specific aptamer and destroyed the sandwichlike structure, the energy transfer efficiency was lowered, leading to PEC response augment. Thus a signal-on PEC aptasensor was constructed. Under 470 nm irradiation at −0.05 V, the PEC aptasensor for CEA determination exhibited a linear range from 0.001 to 2.0 ng mL–1 with a detection limit of 0.47 pg mL–1 at a signal-to-noise ratio of 3 and was satisfactory for clinical sample detection. Since different aptamers can specifically bind to different target molecules, the designed strategy has an expansive application for the construction of versatile PEC platforms.

A novel electrochemiluminescence (ECL) immunosensor for highly sensitive detection of α-fetoprotein (AFP) based on a dual signal amplification strategy was developed. Zinc oxide (ZnO) nanoparticles were employed as the carriers for immobilizing the capture AFP antibody (Ab1) and CdSe quantum dots (QDs). CdSe QDs-functionalized ZnO nanoparticles were used as the tracer to label the signal AFP antibody (Ab2). CdSe QDs-functionalized ZnO nanoparticles were prepared through an amide dehydration reaction and they were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The Ab2 was bound to the CdSe QDs-functionalized ZnO nanoparticles to obtain the detection probe. ZnO nanoparticles could accelerate electron transfer between the detection probe and the electrode, and their large surface area was beneficial for loading more CdSe QDs, leading to an enhanced ECL signal (0.9-fold increase) by a sandwich immunoreaction. This also indicated efficient association of the detection probe on the immunosensor surface. The designed immunoassay showed a wide linear range from 0.5 to 600 ng mL−1 with a detection limit of 0.48 ng mL−1 at a S/N ratio of 3 for AFP detection. The ECL immunosensor exhibited good analytical performance and was successfully applied to clinical sample detection, showing a promising application in ECL biosensing.

A label-free electrochemical biosensing platform has been developed for the first time using carbon nanotubes for facile detection of malondialdehyde, showing high sensitivity and acceptable selectivity with a low detection limit of 0.047 μmol L−1 and a linear response ranging from 0.1 to 90 μmol L−1.

A novel and universal electrochemical strategy for monitoring DNA was developed based on specific cleavage of MspI endonuclease combining with streptavidin–horseradish peroxidase (SA–HRP) conjugate. By introducing the strategy to mycobacterium tuberculosis (MTB) DNA detection, the probe DNA was immobilized on Au electrode via AuS bond and SA–HRP conjugate was linked to probe DNA by biotin–SA specific interaction, which led to the first application in MTB DNA electrochemical detection. This proposed electrochemical method exhibited satisfactory performance which could detect MTB DNA linearly ranging from 10 pM to 100 nM with a detection limit of 2.3 pM. The novel strategy of DNA analysis showed a promising application in clinic diagnostics.Highlights► A signal amplification strategy using MspI endonuclease and HRP was designed. ► A novel and universal electrochemical platform for monitoring DNA was developed. ► A wide concentration range and low detection limit toward detection of MTB DNA.

A competitive immunosensor using CdSe quantum dots (QDs) as a label was highly proposed for the detection of a tumor marker. CdSe QDs were characterized by transmission electron microscope image, photoluminescence spectra and ultraviolet–visible absorption spectra. The fabrication process of the immunosensor was traced with electrochemical impedance spectra. Using α-fetoprotein (AFP) as a model, a simple electrochemiluminescence immunosensing platform based on CdSe QDs using competitive binding between conjugated antibody-CdSe QDs and free AFP with immobilized AFP on Au electrode was developed. Under the optimum conditions, the proposed electrochemiluminescence method could detect AFP ranging from 0.05 to 100 μg/L with a detection limit of 0.005 μg/L. The proposed immunosensor showed good analytical performance and was successfully applied to detecting level of AFP in human serum samples, which would provide a new and promising direction for clinical application.

A versatile photoelectrochemical biosensing platform was developed based on DNA–CdS quantum dots (QDs) sensitized single-walled carbon nanotubes (SWCNTs)-COOH. Combining with cyclic enzymatic amplification, a convenient, sensitive and specific biosensor for the direct detection of microRNAs (miRNAs) was designed, which provided a novel approach for analysis of miRNAs.

A universal and label-free photoelectrochemical cytosensing strategy was designed based on resonance energy transfer (RET) between carbon dots and cysteamine capped gold nanoparticles. RET promoted photo-to-current conversion efficiency and enhanced detection sensitivity. This proposed photoelectrochemical cytosensing platform exhibited a good performance for the assay of tumor cells with overexpressed receptors on cells.