Design And Application Of Electrochemistry Biosensor Based On Electroactive Nanocompatible Materials

Biosensor is a very active research and engineering technical field. Wherein, electrochemical biosensors have valuable applications in clinical diagnosis, environmental monitoring, food and pharmacy industries because of its excellent selectivity, high sensitivity, rapid response, low cost, continuous detection, easy to be miniaturized. In the design and fabrication of electrochemical biosensors, given the characteristics of nano-materials such as the ability of facilitating electron transfer rate, catalytic performance, absorbability, application of nano-materials in bio-electroanalysis plays a meaningful role, in terms of proposing new detection principles and new detection methods/techniques, as well as developing novel yet sensitive electrochemical biosensors. Construction of nanobio-interface, incorporating the distinctive features of nano-materials and biomolecules to exert a synergistic effect, contributes a lot to the development of biosensors. With emphasis on the contruction of nano-films and nano-biomolecule composite interfaces, as well as their application in electrochemical biosensors, this article has carried out the following works:1. A novel amperometric immunosensor has been developed by self-assembling gold nanoparticles (Au NPs) onto a toluidine blue-branched chitosan (CHIT-TB) modified electrode for the sensitive determination of hepatitis B surface antigen (HBsAg) as a model protein. The formation of CHIT-TB composite film not only effectively avoids the leakage of TB and retains its electrochemical activity, but also enhances the conductivity and charge-transport properties of the composite. Further adsorption of Au NPs into the CHIT matrix provides both the interactive sites for the immobilization of HBsAb and a favorable microenvironment to maintain the activity of the HBsAb, in addition prevents leakage of HBsAb molecules from the CHIT-TB/Au NPs/HBsAb film structure efficiently. The morphologies and electrochemistry of the formed nanocomposite film were investigated by using scanning electron microscopy and electrochemical techniques including cyclic voltammetry and electrochemical impedance spectroscopy. The HBsAg concentration was measured through the decrease of amperometric responses in the corresponding specific binding of antigen and antibody. The decreased voltametric values were proportional to the HBsAg concentration in the range of 1 to 200 ng mL-1. The detection of HBsAg levels in five sera obtained from hospital showed acceptable accuracy.2. A novel electrochemical immunosensor for sensitive detection of cancer biomarkerα-fetoprotein (AFP) is described that uses a graphene sheet sensor platform and gold nanoparticles (Au NPs) for immobilization ofα-fetoprotein antibody (anti-AFP). Greatly enhanced sensitivity for the cancer biomarker is based on a dual signal amplification strategy:First, chemically reduced graphene (CRG) functionalized with TB (CRG-TB) is well-dispersed into water through the coulomb repulsion between TB-adsorbed CRG sheets. Meanwhile, functionalized graphene sheets used for the biosensor platform increased the surface area to capture a large amount of antibodies, thus amplifying the detection response. Second, good biocompatibility of Au NPs, which enhances the antibody absorption and promotes electron transfer between redox mediator and the surface of electrode could maintain antibody activity. Therefore a novel and simple electrochemical immunosensor for the ultrasensitive detection of AFP was developed. The developed immunosensor showed a wide linear ranges (0.1-200 ng mL-1) and low detection limits (0.04 ng mL-1). The proposed method showed good precision, high sensitivity, acceptable stability and reproducibility, and could be used as a convenient and cost-effectively tool for hepatitis diagnosis at early stage.3. A new electrochemical immunoassay protocol for sensitive detection ofα-fetoprotein (AFP, as a model) is designed using graphene sheet (CRG) to immobilize mediator toluidine blue (TB)-functionalized biomimetic interface as immunosensing probe and Fe3O4@Au labeled horseradish peroxidase-anti-AFP conjugates (HRP-anti-AFP-Fe3O4@Au) as trace label. The thionine functionalized graphene sheets used for the biosensor platform increased the surface area to capture a large amount of primary antibodies (Ab1), thus amplifying the detection response. Moreover, the low-toxic and high-conductive Fe3O4@Au provided a high capacity nanoparticulate immobilization surface and a facile pathway for electron transfer. The immunosensor displayed a wide range of linear response (1-25 pg mL-1), low detection limit (0.31 pg mL-1), good reproducibility, selectivity and stability. The good performance of the immunosensor is attributed to the graphene sheet's high surface-to-volume ratio which allows the immobilization of a high-level of Ab1, Ab2, Thi and HRP and its good electrical conductivity which can improve the electron transfer among TB, HRP, H2O2 and electrode. The immunosensor was used to detect the AFP contents in serum samples from patients and satisfactory test results were obtained in comparison with the ELIS A test results. Thus, graphene-based labels may provide many potential applications for the detection of different cancer biomarkers.4. A hydrogen peroxide sensor based on the glass carbon electrode modified with the thionine-graphene/gold nanoparticle nanocomposite (CRG-Thi/Au NPs/GCE) was fabricated. The applied potential was-0.3V, and the linearity range was from 0.002 to 0.7 mmol L-1 with a detetion limit of 0.64μmol L-1, the experimental results demonstrate that the fabricated sensor was more sensitive for the H2O2 determination compared with CRG/GCE and CRG-Thi/GCE.