| The direct electrochemistry of enzymes has received increasing attention, studies of direct electron transfer between enzymes and electrodes surface can also provide a platform for fabricating new kinds of mediator free biosensors, enzymatic bioreactors and biomedical devices. However, enzymes exhibit a rather slow rate of heterogeneous electron-transfer at conventional electrodes, because of the deep burying of the electroactive prosthetic groups, the unfavorable orientations of enzymes at electrodes. Therefore, the studies are focusing on selecting ideal electrode materials, such as cabon nanotubes, mesoporous materials and biomaterials to enhance the direct electron transfer between the enzymes and underlying electrodes. Recently, a series of porous materials such as clay, montmorillonite, porous alumina and zeolite have been used as immobilization matrices. Mesoporous silica (MS) particles with controlled morphology are receiving increasing attention for their potential applications as compartments for immobilization, and their useful application as enzyme carriers has been suggested. However, like other inorganic mesoporous materials, MS has poor conductivity and is not suitable for the direct electrochemistry. To improve this deficiency, metal nanoparticles such as gold, silver, platinum, etc, could be introduced to the electrode modified materials. These kinds of metal nanoparticles have excellent conductivity, catalytic property and biocompatibility. They can perform as "electronic wires" to enhance the electron transfer between redox centers in enzymes and electrode surfaces, and as catalysts to increase electrochemical reactions. However, these nanoparticles are intended to agglomerate. To prevent aggregation, it is necessary to use protective agents, such as small organic molecules or polymers. Highly branched dendritic macromolecules poly(amidoamine) (PAMAM) could also be used to modify electrode surface due to their good biocompatibility and adequate functional groups for chemical fixation. It was reported that the material was capable of increasing the concentration of hydrophobic molecules at the electrode-solution interface, improving the sensitivity as well as the selectivity of certain specific electrochemical reactions. With this in view, the mai research is as follows:1. A hybrid systems of mesoporous silica (MS) particle coated with polypyrrole (PPy) were constructed through a chemical polymerization of pyrrole in the presence of the MS particles. The MS-PPy composite particles immobilized hemoglobin (Hb) were used to modify a glassy carbon electrode (GCE) for detecting the electrocatalytic response to the reduction of hydrogen peroxide. The structure of composite particles and the performance of biosensors were characterized by SEM, TEM, FTIR, cyclic voltammetry (CV) and amperometric measurements, respectively. The results show that the PPy shell is uniformly coated over the silica surface without using any agents to modify the MS particles. Under optimal conditions, the sensors had a fast response of hydrogen peroxide (H2O2). The catalytic currents are linear to the concentrations of H2O2 in the ranges of 0.01 to 1.2 mM and the corresponding detection limits are 0.01 mM (S/N=3).2. A hybrid system of mesoporous silica (MS) particle incorporated with poly(amidoamine) (PAMAM) dendrimer-encapsulated platinum nanoparticles (Pt-DENs) was constructed in a neutral aqueous solution through electrostatic interaction. The MS/Pt-DENs composite particles immobilized with glucose oxidase (GOx) were used to modify a glassy carbon electrode (GCE) for detecting the electrocatalytic response to the reduction of glucose. Pt-DENs can improve the conductivity of MS and enhance the electron transfer between redox centers in enzymes and electrode surfaces. The structure of composite particles and the performance of MS/Pt-DENs modified electrodes were characterized by transmission electron microscopy (TEM), N2 sorption characterization method, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and amerometric measurements. The MS/Pt-DENs/GOx modified electrodes, which had a fast response of glucose oxidase less than 3 s, could be used for the determination of glucose ranging from 0.02 to 10 mM. The detection limits were 4μM at signal-to-noise ratio of 3.3. A hybrid system of clay clusters incorporated with poly(amidoamine) dendrimers-encapsulated platinum nanoparticles (Pt-DENs) was constructed in a neutral aqueous solution through electrostatic interaction. The Pt-DENs/clay nanohybrid immobilized glucose oxidase (GOx) was used to modify a glassy carbon electrode (GCE) for detecting the electrocatalytic response to the reduction of glucose. The structure of nanohybrid and the performance of biosensors were characterized by cyclic voltammetry (CV) and amperometric measurements, respectively. The sensors, which had a fast response to glucose oxidase less than 3 s, could be used for determination of glucose ranging from 0.01 to 16 mM. The detection limit is 4μM with a signal to noise ratio of 3.4. A hybrid system of titanium dioxide nanotubes (TNTs) incorporated with poly(amidoamine) dendrimers-encapsulated platinum nanoparticles (Pt-DENs) was constructed in a neutral aqueous solution through electrostatic interaction. The TNTs/Pt-DENs nanohybrids immobilized glucose oxidase (GOx) were used to modify a glassy carbon electrode (GCE) for detecting the electrocatalytic response to the reduction of glucose. The structures of nanohybrids were characterized by TEM, XRD and FT-IR, the performance of modified electrodes was characterized by cyclic voltammetry (CV) and amerometric measurements, respectively. The modified electrodes, which had a fast response of glucose oxidase less than 3 s, could be used for the determination of glucose oxidase ranging from 2μM to 12 mM. The detection limits were 1μM at signal-to-noise ratio of 3.
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