The Application Of Nanoparticles In The Biosensors And The Study Of Chemically Modified Electrodes

From 1990s, nanoparticles have been widely development, many studies have been reported about nanoparticles' preparetion and improvement, and they have gotten the best interest in the application of many areas because of their catalyze characteristics. Recently, nanoparticles have been the fundamentally class of materials in the preparation of the biosensor due to their physical and chemical properties.In recent years, electrochemical biosensor has been widely used in clinical diagnostics, biochemical analyses, environmental monitoring and food quality control, because of its merits such as simple preparation, high sensitivity and selectivity. However, the study of excellent methods and new materials used to immobilize biomolecules is one of the important works in the development of the electrochemical biosensor. In this paper, several advanced nanoparticles are provided to immobilize biomolecules.As an important application of chemically modified electrodes (CMEs) in analysis areas, many studies have been reported about the investigation of the CMES. In analysis,CMEs can improve the selectivity and sensitivity of the detection based on the reaction of electrocatalysis. So, CMEs has been widely used in the examination of H₂O₂ and hydroxybenzene.The main works and conclusions are included as follows:The first part studied the application of Au and CuO nanoparticles in the preparation of the biosensor. Nanoparticles are the excellent materials for the improvement of the biosensor, based on the great large specific surface area, excellent biocompatibility and good electronics conduct. The second part studied the directly electrocatalytic reduction of H₂O₂, this method minimized the limitation of the immobilized enzyme/protein on the surface of the electrode is facilitated to denature. Moreover, the proposed sensor possessed high sensitivity and high stability.(1) A stable PAI film was formed on the surface of GCE. The mixture of horseradish peroxidase (HRP), Glutaraldehyde (GA), Albumin bovine (BSA) and colloidal gold was immobilized on the surface of PAI modified GCE by a self-assembled method to prepare a novel H₂O₂ biosensor. At the same time, we studied the electrochemical characters of the biosensor using CV and EIS. The experiments showed that the composite film could significantly retain the catalytic activity of the immobilized enzyme. The proposed sensor had a fast response to H₂O₂ (<10 s) and the catalytic currents had a linear relationship with the H₂O₂ concentration in the range of 3.0×10^-6-8.0×10^-3 mol·L^-1, with a detection limit of 1.2×10^-6mol·L^-1. The biosensor exhibited fast response, high sensitivity and good stability.(2) A novel and effective electrochemical immunosensor for the rapid determination ofα-1-fetoprotein (AFP), based on electrostatic interaction of CdS nanoparticles (nano-CdS) and thionine (Thi) on poly-congo red (PCR) modified glass carbon electrode (GCE), alternately was developed. The formation of the {nano-CdS/Thi}₂ bilayer films showed a good electrochemical activity, and a couple of stable and well-defined Thi redox peaks were obtained in pH 7.0 phosphate buffer solution (PBS). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were adopted to confirm the successful stepwise layer-by-layer assembly (LBL) procedure of the immunosensor. Horseradish peroxidase (HRP) was employed to block sites against non-specific binding instead of bovine serum albumin (BSA) and amplify the response currents. Tests showed that the reduction current of the immunosensor was proportional to AFP concentration in the range of 0.30-250.00 ng·mL^-1 with a detection limit of 0.12 ng·mL^-1. Moreover, the prepared immunosensor exhibited high sensitivity and good stability, would be valuable for clinical immunoassay of AFP.(3) A sensitive amperometric immunosensor for carcinoembryonic antigen (CEA) detection was prepared. Firstly, a porous nano-structure gold film was formed on glassy carbon electrode (GCE) by electrochemical reduction of HAuCl₄ solution. Then negatively charged CdS nanoparticles (nano-CdS) were assembled on the nano-Au modified electrode. Subsequently, separately assembled positively charged thionine (Thi) and negatively charged CdS nanoparticles (nano-CdS) based on electrostatic interaction to immobilize antibody. Finally, a competitive immunoassay format was employed for the detection of carcinoembryonic antigen (CEA) with bovine serum albumin (BSA) to block sites against non-specific binding. Under optimal conditions, the CEA could be detected in the range of 0.10-80.00 ng·mL^-1 with a detection limit of 0.03 ng·mL^-1. Importantly, the resultant immunosensor was a potential biosensor for mimicking other immunosensors.(4) A novel electrochemical sensor for the detection of hydrogen peroxide (H₂O₂) was proposed based on immobilizing Copper oxide nanoparticles (nano-CuO) on Nafion (Nf) membrane coated Pt electrode. The electrocatalytical behaviors of the sensor were also investigated by CV and Chronoamperometry. Tests showed that nano-CuO exhibited a remarkable electrocatalytic activity for the reduction of H₂O₂. Under optimal conditions, the electrocatalytic response of the sensor was proportional to the H₂O₂ concentration in the range of 1.5×10^-7-9.0×10^-3mol·L^-1 with a detection limit down to 6.0×10^-8mol·L^-1 at 3 a, and achieved 95 % of the steady-state current in 5 s. The low detection limit, wide linear range and high sensitivity of the sensor make it valuable for further application.