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DNA-templated silver nanoclusters (DNA/AgNCs) serve as a useful electrochemical sensing nanomaterial characterized by excellent electroactivity and good stability, while the effect of surrounding nucleotides on their electroactivity has not been studied. Herein, we validated a nucleotide-assisted enhancement mechanism of the DNA/AgNCs electroactivity caused by T-rich nucleic acid sequences in the vicinity of AgNCs. Based on the T-rich nucleic acid-enhanced AgNCs (NAE-AgNCs) combined with hybrid chain reaction (HCR), a novel signal-enhanced electrochemical biosensing platform was established for the ultrasensitive detection of miRNA. In the presence of target miRNA-155, HCR could be triggered to generate duplex strands containing both numerous AgNC synthesis sites and T-rich overhang strands upon the electrode. With the electrodeposition of adjacent AgNCs on the electrode, the larger oxidation potential of T-rich nucleic acid leaded to stronger electron-accepting capacity, which could contribute to increased current responses. The T-rich NAE HCR electrochemical strategy resulted in a detection limit of 0.39 fM for miRNA-155 detection, one order of magnitude lower than conventional HCR-based electrochemical sensors. This T-rich nucleic acid-assisted enhancement mechanism provided a new direction to construct highly sensitive, label-free, low-cost, and simple sensing platforms for applications in biomarker assays and clinic diagnosis.

We report an ultrasensitive electrochemical immunosensor designed for the detection of protein biomarkers using horseradish peroxidase (HRP)-loaded silica-poly(acrylic acid) brushes (SiO2-SPAABs) as labels. HRP could be efficiently and stably accommodated in the three-dimensional architecture of the SiO2-SPAABs and the SiO2-SPAABs-HRP exhibited high catalytic performance towards o-phenylenediamine (OPD) oxidation in the presence of H2O2, which resulted in significant differential pulse voltammetric (DPV) response change and color change. Using human IgG (HIgG) as a model analyte, a sandwich-type immunosensor was constructed. In particular, graphene oxide (GO) and SiO2-SPAABs-HRP were used to immobilize capture antibody (Ab1) and bind a layer of detection antibody (Ab2), respectively. The current biosensor exhibited a good linear response of HIgG from 100pg/mL to 100μg/mL with a detection limit of 50pg/mL (S/N=5). The sensitivity was 6.70-fold higher than the conventional enzyme-linked immunosorbent assays. The immunosensor results were validated through the detection of HIgG in serum samples.

Construction of novel photoelectrochemical (PEC) materials with unique structures can effectively improve the photoelectric conversion efficiency. Here, a self-supported Cu2O@Cu-MOF/copper mesh (CM) nanobelt arrays with high specific surface area, high orientation, and high photoelectric conversion performance is obtained by in-situ grown strategy. Such PEC aptasensor is constructed based on the Cu2O@Cu-MOF/CM combined with rolling circle amplification and enzymatic biocatalytic precipitation for vascular endothelial growth factor 165 analysis. This strategy achieves excellent cooperative signal amplification, which greatly improves the detection sensitivity. The PEC aptasensor exhibited a wide calibration ranged from 10 to 1 × 108 fM with a detection limit down to 2.3 fM (S/N = 3). The construction of semiconductor@MOFs has developed the potential application of MOFs in photoelectrochemical and found a reliable path for ultrasensitive detection of biomarkers.

An ultrasensitive photoelectrochemical (PEC) biosensor was constructed based on gold nanoparticles (Au NPs)/tungsten sulfide nanorod array (WS2 NA) photoelectrode as the PEC matrix and silver nanoparticles/flake-like zinc metal-organic framework (Ag/ZnMOF) nanozyme with the peroxidase mimetic enzyme property for sensitive detection of bleomycin (BLM). In particular, Au/WS2 and Ag/ZnMOF were linked by thiolate DNA1 and DNA2 strand, respectively, and the Au/WS2–Ag/ZnMOF probe was prepared via hybridization reaction between the two DNAs. The introduction of Ag/ZnMOF in the probe offers two functions: i) the steric hindrance effect can effectively impede electron transport and reduce the photocurrent; ii) Ag/ZnMOF nanozyme can also be used as mimic peroxidase to effectively catalyze 3,3-diaminobenzidine (DAB) to produce the relevant precipitation, which will further reduce photocurrent and eliminate false positive signals. When BLM exists, BLM with Fe2+ as irreversible cofactor can specifically recognize and cleave of the 5′-GC-3′ active site of DNA2, resulting in reduced precipitation deposited on the electrode and recovery of PEC signal. The highly sensitive PEC biosensor exhibits a the linear strategy from 0.5 nM to 500 nM with a detection limit down to 0.18 nM. Further, the unique strategy was conducted in biological samples for BLM detection with satisfactory consequence, offering available and efficient pathway for disease diagnosis.

Photoelectrochemical (PEC) biosensor for highly sensitive detection of breast cancer biomarker human epidermal growth factor receptor-2 (HER2) is reported utilizing a dual signal amplification strategy. The biosensor was prepared based on tungsten sulfide nanowire array on Ti mesh (WS2 NW/TM). Such WS2 NW/TM electrode can generate photoelectric signal under visible light excitation. The HER2 aptamer was wrapped onto the nanowire array surface for specific binding with HER2 molecules, and gold nanoparticles (Au NPs) that modified with glucose oxidase (GOx) and HER2 binding peptide was utilized for signal amplification. The H2O2 that generated by GOx catalyzed glucose reaction and localized surface plasmon resonance of Au NPs can both enhance the PEC current intensity of the biosensor, leading to dual signal amplification. The PEC current intensity is enhanced linearly with HER2 concentration in the 0.5–10 ng/mL range with limit of detection of 0.36 ng/mL. Such biosensor was applied for the detection of HER2 in breast cancer serum samples with detection results in good agreement with commercial ELISA results.

In this work, based on the fact that pyrophosphate (PPi) could regulate the activity of Zn 2+ -dependent DNAzyme, we for the first time report a fluorescence turn-on sensing system for alkaline phosphatase (ALP) with improved sensitivity via nonprotein-enzymatic signal amplification. A catalytic and molecular beacon (CAMB) design was employed to further improve its sensitivity. Taking advantage of the strong interactions between PPi and the Zn 2+ , the cofactor Zn 2+ was caged, and the DNAzyme activity was effectively inhibited. The introduction of ALP, however, could catalyze the hydrolysis of PPi and release free Zn 2+ , resulting in the activation of DNAzyme to catalyze the cleavage of the molecular beacon substrate with a remarkable increase of fluorescent signal. These optimized designs together allow a high sensitivity for ALP, with a detection limit of 20 pM observed, much lower than previously reported methods. It has also been used for detection of ALP in human serum with satisfactory results, demonstrating its potential applications in clinical diagnosis.

A universal amplified sensing strategy based on endonuclease was developed for designing fluorescence aptasensors. By employing hairpin-structured design for both recognition and reporter probes to decrease background signal, and a nicking endonuclease to perform target-triggered enzymatic recycling amplification, the proposed biosensor showed high sensitivity to target protein. To demonstrate the feasibility of the design, immunoglobulin E (IgE) was studied as a model target. Upon the addition of target protein, the specific formation of IgE/aptamer complex induced the releasing of the 37-mer fragment which partially hybridized with the molecular beacon (MB) probe. In the presence of endonuclease Nt.BbvCI, the MB was cleaved into two parts. Then, the released 37-mer fragment hybridized with another MB, and triggered the second cycle of cleavage, leading to an accumulation of fluorescence signals. Under the optimal conditions, a detection limit of 5 pM was obtained. The proposed sensing system was used for detection of IgE in complex biological samples with satisfactory results.

A new colorimetric immunoassay for the detection of cancer biomarker prostate specific antigen (PSA) was developed based on the intrinsic peroxidase activity of graphene oxide (GO). GO can catalyze the reaction of hydroquinone in the presence of H2O2 to produce a brown color solution. Secondary antibody (Ab2) functionalized GO (GO-Ab2) was used as label for the immunoassay, while magnetic bead (MB) was selected to immobilize primary anti-PSA antibody (Ab1). In the presence of PSA, an immunocomplex, sandwiching the antigen protein, is formed between the GO-Ab2 and MB-Ab1. With the separation of the immunocomplex using an external magnetic field, different amounts of GO-Ab2 in the solution were mixed with hydroquinone and H2O2 solution and displaying colors. Different colors corresponding to different concentrations of PSA can be directly detected with eyes. Such a simple immunoassay holds great potential as sensitive, selective and point-of-care (POC) tool for clinical diagnosis of cancer biomarkers.

A nonenzymatic electrochemical biosensor was developed for the detection of glucose based on an electrode modified with palladium nanoparticles (PdNPs)-functioned graphene (nafion-graphene). The palladium nanoparticle-graphene nanohybrids were synthesized using an in situ reduction process. Nafion-graphene was first assembled onto an electrode to chemically adsorb Pd(2+). And Pd(2+) was subsequently reduced by hydrazine hydrate to form PdNPs in situ. Such a PdNPs-graphene nanohybrids-based electrode shows a very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium. The proposed biosensor can be applied to the quantification of glucose with a wide linear range covering from 10 μM to 5mM (R=0.998) with a low detection limit of 1 μM. The experiment results also showed that the sensor exhibits good reproducibility and long-term stability, as well as high selectivity with no interference from other potential competing species.

A novel electrochemical immunosensor for sensitive detection of cancer biomarker prostate specific antigen (PSA) based on nitrodopamine (NDA) functionalized iron oxide nanoparticles (NDA–Fe 3 O 4 ) is described. NDA–Fe 3 O 4 was used both for the immobilization of primary anti-PSA antibody (Ab 1 ) and as secondary anti-PSA antibody (Ab 2 ) label. For the preparation of the label, mediator thionine (TH) was first conjugated onto NDA–Fe 3 O 4 based on the amino groups of NDA, and then the amino group of TH was used to immobilize horseradish peroxidase (HRP) and Ab 2 . Due to the high amount of NDA anchored onto Fe 3 O 4 surface, the loading of antibodies as well as mediator and enzyme onto NDA–Fe 3 O 4 was substantially increased, which increased the sensitivity of the immunosensor. The resulting immunosensor displayed a wide range of linear response (0.005–50 ng/mL), low detection limit (4 pg/mL), good reproducibility and stability. The immunosensor was used to detect the PSA contents in serum samples with satisfactory results.

Highly ordered Ni nanowire arrays (NiNWAs) were synthesized for the first time using a template-directed electropolymerization strategy with a nanopore polycarbonate (PC) membrane template, and their morphological characterization were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). A NiNWAs based electrode shows very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium, which has been utilized as the basis of the fabrication of a nonenzymatic biosensor for electrochemical detection of glucose. The biosensor can be applied to the quantification of glucose with a linear range covering from 5.0x10(-7) to 7.0x10(-3) M, a high sensitivity of 1043 microA mM(-1) cm(-2), and a low detection limit of 1x10(-7) M. The experiment results also showed that the sensor exhibits good reproducibility and long-term stability, as well as high selectivity with no interference from other oxidable species.

In this paper, we report a kind of ordered 3D Au nano-prickle clusters by directly electrodeposited on glassy carbon electrode utilizing the spatial obstruction/direction of the polycarbonate membrane. The proposed 3D nanoclusters are applied to fabricate a sandwich-type electrochemical immunosensor with human IgG as a model analyte. The electrodeposited Au nanoclusters build direct electrical contact and immobilization interface for protein molecules, which do not need post-modification and positioning. Scanning electron microscopy, cyclic voltammetry and alternating current impedance spectroscopy were used to investigate the properties of the modified interface. The deposited Au nanoclusters are stable with good biocompatibility, large specific surface area and high electron exchange capability. Under the optimized experimental conditions, a wide linear range from 1.0 to 10000.0 ng/mL was reached with a detection limit of 0.5 ng/mL. The calibration curve fits a second-order polynomial equation very well (R2 = 0.9914). The developed immunosensor based on Au nano-prickle clusters possesses advantages such as simple fabrication, fast response, low detection limit, wide linear range, easy regeneration, excellent reproducibility and long stability. To our knowledge, the Au nanostructure of special ordered 3D nano-prickle clusters is new for electrochemical immunosensor.

Platinum nanowires (PtNWs) prepared by electrodeposition method with the help of porous anodic aluminum oxide (AAO) templates have been solubilized in chitosan (CHIT) together with carbon nantubes (CNTs) to form a PtNW-CNT-CHIT organic-inorganic system. The resulting PtNW-CNT-CHIT material brings capabilities for utilizing synergic action of PtNWs and CNTs to facilitate electron-transfer process in electrochemical sensor design. The PtNW-CNT-CHIT film modified electrode offered a significant decrease in the overvoltage for the hydrogen peroxide and showed to be excellent amperometric sensors for hydrogen peroxide at -0.1 V over a wide range of concentrations, and the sensitivity is 260 microAmM-1cm-2. As an application example, by linking glucose oxidase (GOx), an amplified biosensor toward glucose was prepared. The glucose biosensor exhibits a selective determination of glucose at -0.1 V with a linear response range of 5 x 10(-6) to 1.5 x 10(-2)M with a correlation coefficient of 0.997, and response time