Non-enzymatic electrochemical hydrogen peroxide biosensor based on reduction graphene oxide-persimmon tannin­platinum nanocomposite.

Hydrogen peroxide (H2O2) is one of the most universal and essential ingredients in distinct biological tissues. Herein, a novel non-enzymatic sensor based on reduction graphene oxide-persimmon tannin­platinum nanocomposite (RGO-PT-Pt) was exploited for H2O2 detection. RGO-PT-Pt nanocomposite was prepared by reduction procedure with ascorbic acid as reducing agent and characterized by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV-vis) and Fourier infrared spectroscopy (FT-IR). Taking advantage of high electro-catalytic efficiency of Pt nanoparticles, high electronic conductivity and large surface area of RGO, and significant adsorption ability of PT on metal ions and its prevention of agglomeration to promote RGO dispersion, RGO-PT-Pt nanocomposite revealed better catalytic ability towards H2O2 via a synergistic effect. Under the optimal conditions, the RGO-PT-Pt non-enzymatic biosensor exhibited outstanding electrocatalytic activity towards H2O2 reduction. The amperometric response demonstrated a linear relationship with H2O2 concentration from 1.0 to100 µM with the correlation coefficient of 0.9931. The limit of detection was 0.26 µM (S/N = 3) and the response time was 3 s. Furthermore, the fabricated sensor exhibited a practical applicability in the quantification of H2O2 in human serum samples with an excellent recovery rate. Due to excellent performance such as fast response time, low detection limit, high stability and selectivity, the RGO-PT-Pt non-enzymatic biosensor has potential application in clinical diagnostics.

Label-free electrochemical aptasensor for detection of alpha-fetoprotein based on AFP-aptamer and thionin/reduced graphene oxide/gold nanoparticles.

Sensitive and accurate detection of tumor markers is critical to early diagnosis, point-of-care and portable medical supervision. Alpha fetoprotein (AFP) is an important clinical tumor marker for hepatocellular carcinoma (HCC), and the concentration of AFP in human serum is related to the stage of HCC. In this paper, a label-free electrochemical aptasensor for AFP detection was fabricated using AFP-aptamer as the recognition molecule and thionin/reduced graphene oxide/gold nanoparticles (TH/RGO/Au NPs) as the sensor platform. With high electrocatalytic property and large specific surface area, RGO and Au NPs were employed on the screen-printed carbon electrode to load TH molecules. The TH not only acted as a bridging molecule to effectively capture and immobilize AFP-aptamer, but as the electron transfer mediator to provide the electrochemical signal. The AFP detection was based on the monitoring of the electrochemical current response change of TH by the differential pulse voltammetry. Under optimal conditions, the electrochemical responses were proportional to the AFP concentration in the range of 0.1-100.0 µg/mL. The limit of detection was 0.050 µg/mL at a signal-to-noise ratio of 3. The proposed method may provide a promising application of aptamer with the properties of facile procedure, low cost, high selectivity in clinic.

Graphene and Au NPs co-mediated enzymatic silver deposition for the ultrasensitive electrochemical detection of cholesterol.

Cholesterol is an essential ingredient in mammals, and serum cholesterol is a major component of atherosclerotic plaques. The level of cholesterol in human serum has become an important index for clinical diagnosis and prevention of cardiovascular disease. In this paper, a simple and ultrasensitive cholesterol biosensor based on graphene oxide (GO) and gold nanoparticles (Au NPs) co-mediated enzymatic silver deposition was designed by immobilizing cholesterol oxidase (CHOD), cholesterol esterase (CHER) and GO onto the surface of Au NPs modified screen-printed carbon electrode (SPE). Under the synergistic effect of CHER, CHOD and GO, the cholesterol was hydrolyzed to generate hydrogen peroxide, which can reduce the silver (Ag) ions in the solution to metallic Ag which deposited on the surface of Au NPs modified SPE. The ultrasensitive detection of cholesterol was achieved by anodic stripping voltammetry measurement of the enzymatically deposited Ag. Under optimal conditions, the anodic stripping peak current of Ag increased with the increasing cholesterol concentration in the range from 0.01µg/mL to 5000µg/mL with a limit of detection of 0.001µg/mL (S/N = 3). In addition, the ultrasensitive cholesterol biosensor exhibited higher specificity, acceptable reproducibility and excellent recoveries for cholesterol detection.

A Fe3O4@Au-basedpseudo-homogeneous electrochemical immunosensor for AFP measurement using AFP antibody-GNPs-HRP as detection probe.

In this study, a Fe3O4@Au-based pseudo-homogeneous electrochemical immunosensor was prepared for detection of alpha fetoprotein (AFP), a well-known hepatocellular carcinoma biomarker. The primary antibody (Ab1) was immobilized on Fe3O4@Au NPs as the capture probe. Horseradish peroxidase (HRP) and secondary antibody (Ab2) were conjugated on gold nanoparticles (GNPs) through electrostatic adsorption to form signal-amplifying labels. In the presence of AFP, a sandwich immunocomplex was formed via specific recognition of antigen-antibody in a Fe3O4@Au-basedpseudo-homogeneousreaction system. After the immunocomplex was captured to the surface of magnetic glassy carbon electrode (MGCE), the labeling HRP catalyzed the decomposition of H2O2, resulting in a substantial current for the quantitative detection of AFP. The amperometric (i-t) method was employed to record the response signal of the immunosensor based on the catalysis of the immobilized HRP toward the reduction of H2O2 with hydroquinone (HQ) as the redox mediator. Under the optimal conditions, the amperometric current response presented a linear relationship with AFP concentration over the range of 20 ng/mL-100 ng/mLwith a correlation coefficient of 0.9940, and the detection limit was 0.64 ng/mL at signal/noise [S/N] = 3. Moreover, the electrochemical immunosensor exhibited higher anti-interference ability, acceptable reproducibility and long-term stability for AFP detection.

Ultrasensitive cholesterol biosensor based on enzymatic silver deposition on gold nanoparticles modified screen-printed carbon electrode.

Cholesterol is one of the essential structural constituents of cell membranes. Determination of cholesterol is of great importance in clinical analysis because the level of cholesterol in serum is an indicator in the diagnosis and prevention of heart diseases. In this work, a simple and ultrasensitive cholesterol biosensor based on enzymatic silver deposition was designed by immobilizing cholesterol oxidase (CHOD) and cholesterol esterase (CHER) onto the surface of gold nanoparticles (Au NPs) modified screen-printed carbon electrode (SPE). By the catalytic action of CHER and CHOD, the cholesterol was hydrolyzed to generate hydrogen peroxide (H2O2) which can reduced the silver (Ag) ions in the solution for the deposition of metallic Ag on the surface of Au NPs modified SPE. The ultrasensitive detection of cholesterol was achieved by anodic stripping voltammetry (ASV) measurement of the enzymatically deposited Ag. The influence of relevant experimental variables was optimized. The anodic stripping peak current of Ag depended linearly on the concentration of cholesterol in the range of 5-5000µg/mL with the regression correlation coefficient of 0.9983. A detection limit of 3.0µg/mL was attained by 3 sigma-rule. In addition, the ultrasensitive cholesterol biosensor exhibited higher specificity, acceptable reproducibility and excellent recoveries for cholesterol detection.