Electrochemical Biosensors Based On Nanocomposites

Electrochemical bioanalytical technology based on microelectronics technology, materials technology, biotechnology and nanotechnology is an emerging technology. Electrochemical biosensor have widespread applications in the detection of some tumor markers, glucose and hydrogen peroxide due to its biological specifity. Compared with other analytical methods such as enzyme-linked immunosorbent assays and single radial immunodiffusion assays, electrochemical biosensor have many advantages such as high sensitivity, low cast, fast analysis and simplicity in fabrication procedures. Novel nanocomposites（NCPs） have received great attention on catalysis and electrocatalysis in the past few years because of their unique physical and chemical properties. This is attributed mainly to its high surface area to mass ratio and excellent biocompatibility.With the development of electrochemical biosensor in recent years, they have become the most important problems of high-sensitive and high-steady biosensor that how to find more efficient nanomaterials and how to stably fix the small molecules on the modified electrodes. In this paper, we used some new nanomaterials such as nano-Prussian Blue, nano-cobalt oxide, nano-cuprous oxide and nickel hydroxide and combined with easy film-forming materials dopamine for the research of electrochemical biosensors. The tests using scanning electron microscope（SEM）, X-ray diffraction（XRD）, Transmission electron microscopy（TEM）, infrared chromatography（FT-IR） for the characterization of nanocomposites morphology. Electrochemical techniques were also used as tools for the characterization of the fabrication process and the performance of electrode. The main research content is as follows:（1） In this part, prussian blue（PB） coated gold nanoparticles（Au NPs） were firstly prepared with in situ method. Then, polydopamine（PDA） wrapped Au-PB was synthesized by using the characteristic of one-step oxidative polymerization of dopamine. The bioinspired surface enriched amino and hydroxyl groups was further used as a support to anchor active platinum nanoparticles（Pt NPs）. Horseradish peroxidase（HRP） functionalized Au-PB-PDA-Pt nanocomposites was also used for the fabrication of H₂O₂ biosensor. By taking advantages of the excellent biocompatibility and film forming ability of PDA and the large surface area and high biocompatibility of Pt NPs and the synergistic employ of PB, Pt and HRP, the HRP functionalized nanocomposites modified electrode exhibited excellent electroreduction activity to H₂O₂. Under optimum conditions, a linear range of the resulted H₂O₂ sensor is from 2.0×10^-7 mol L^-1 to 1.0×10^-3 mol L^-1.（2） A sensitive triple signal amplifying electrochemical biosensor based on a novel horseradish peroxidase（HRP） functionalized Co₃O₄-Pt nanocomposite was fabricated for the detection of H₂O₂. The Co₃O₄ nanoparticles（Co₃O₄ NPs） were successfully synthesized with hydrothermal method. The study found that the catalytic performance of Co₃O₄ NPs was synergistic with Pt nanoparticles’. At the same time, as nanoparticles, Co₃O₄ and Pt greatly enhanced the load and biology catalytic activity of HRP due to its large specific surface and excellent biocompatibility. Under optimal experimental conditions, the dynamic range of the resulted biosensor for the detection of H₂O₂ is from 2.0 μM to 7.1 mM with a detection limit of 0.9 μM（S/N=3）.（3） A novel biomolecular immobilization strategy based on Cu2 O rhombic dodecahedra–polydopamine–gold nanoparticles nanocomposite was used for the detection of alpha-fetoprotein（AFP）. Cu2 O rhombic dodecahedra as a new kind of Cu2 O nanocrystals having excellent catalytic properties were coated with bio-functional polydopamine（PDA） by a simple self-polymerization in mild basic solution. Then, highly loaded and uniformly dispersed gold nanoparticles（Au NPs） were deposited on Cu₂O-PDA through in situ deposition. Under optimal conditions, a linear relationship between the CV peak current and the logarithm of AFP concentration was obtained from 0.001 to 100 ng mL^-1 with a detection limit of 0.6 pg mL^-1 at the signal-to-noise ratio of 3. The high sensitivity and stability, low cost and simplicity in fabrication procedures of the proposed immunosensor provides potential applications for clinical immunoassays.（4） In this part, GE/Ni（OH）2-PDA-Pt modified electrode was successfully prepared by layer-by-layer assembly method, and the modified electrode was used to detect hydrogen peroxide concentration. Under optimum conditions, the detection range of H₂O₂ concentration was obtained from 0.002 mol L^-1 to 0.1 mol L^-1 with a detection limit of 0.001 mol L^-1. It was found that, under alkaline conditions, nickel hydroxide has high electrocatalytic activity. Introducing of polydopamine effectively increased the loading of platinum nano-particles and it greatly enhanced the conductivity of the electrode surface and increased the contact area of the reaction. Therefore, the proposed modified electrode exhibits good electrocatalytic reduction activity to H₂O₂. In addition, the H₂O₂ sensor have low cost, simple preparation process and strong stability.