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Study On Electrochemical Biosensors Based On Carbon Mesoporous Materials

Posted on:2010-12-26Degree:DoctorType:Dissertation
Country:ChinaCandidate:C P YouFull Text:PDF
GTID:1118360278954371Subject:Analytical Chemistry
Abstract/Summary:PDF Full Text Request
Biosensors,as an interdisciplinary frontier related to chemistry,biology,physics, medical science and electronics,will have broad applications in clinical medicine, industry,agriculture and environment protection.Biosensing technology will also become the new growing point between information technology and biological technology during the development of intelligent economy in 21 century. Electrochemical biosensor is extensively investigated and becomes one of the most practical and prospective devices among all kinds of biosensors.It is composed of the biomaterial as a receptor and an electrode as a transducer,detecting the generated electrical signals.A key factor in biosensor development is the immobilization of biomolecules.It is very significant to find a reliable strategy to immobilize biomolecules,retaining their high activity and meanwhile allowing the effective electron-transfer(ET) between the redox centers and the electrode surface.Carbon based nanomaterials have drawn increasing attention because of their good conductivity and chemical stability.However,bioelectrochemical studies of redox proteins/electrode typically require mediators to promote ET between the redox sites and the electrode surface.Hence,when no mediators present,only a few redox proteins performed direct ET on electrodes modified with carbon nanotubes(CNTs). Thus it is important for the understanding on protein properties and the development of bioelectrochemical devices to study the direct ET of redox proteins.It is well known that two factors seriously affect the redox behavior and bio-activity of the immobilized proteins.One is the protein-loading capability of the material;the other is the biocompatibility and the electro-catalytic performance of the matrix.Nanomaterials,such as nanoparticles,CNTs,nanoporous metal oxides and so on,can immobilize bio-components effectively and have great potentials in the application of biosensors,arousing increasing research interest.Carbon mesoporous materials(CMMs),a new type of nanostructured carbon materials,have recently shown many unique properties and attracted growing interest in diverse fields from catalyst carriers,absorbents to electronic devices.CMMs are composed of carbon nanorods with highly ordered arrays.Thus CMMs not only have good conductivity and chemical stability like CNTs,but also show many unique properties,such as highly-ordered and tailored mesostructures,much narrow pore size distributions,large surface areas(up to ca.2000 m2 g-1) and large porosity(up to ca.1.5 cm3 g-1).That means it is possible to design the selectivity of substrates for biomolecule immobilization,by varying the pore diameter,mesoscopic topology and charge of CMMs.All of these advantages make them greatly promising in the realm of protein immobilization and heterogeneous ET.Besides,CMMs can be easily prepared via the hard templating strategy with low cost and free from any impurities if silica 'mold' is fully etched away.While up to now,many other potential advantages of CMMs,e.g. biocompatibility and eletrocatalytic properties,have rarely been addressed,especially for its applications in immobilizing proteins and fabricating biosensors.The electrode modification with novel nanomaterials can immobilize biomolecules effectively and promote the direct ET between redox centers and electrodes,thus develop a new generation of biosensors and other bio-devices. Therefore,this issue is of great theoretical and practical significance.This dissertation includes six chapters as follows:In Chapter One,we introduced the research and development of nanomaterials and biosensors,respectively.Then we proposed a scheme of functional nanomaterials-modified electrodes for protein immobilization and research on ET, electro-catalysis and biosensing.Finally we outlined the experimental ideas and the research purposes of this thesis.In Chapter Two,we studied the electrochemistry and biosensing of glucose oxidase(GOx) based on Pt-dispersed CMM.Platinum nanoparticles(PtNPs) provided with excellent conductivity and catalytic properties can effectively enhance conductive and electrocatalytic performance of the prepared nanocomposite. Compared with the pure two dimensional(2D-) CMM,CMM dispersed with PtNPs enhances the electron communication and redox reversibility of redox enzyme at the modified electrode,due to the cooperative effect of PtNPs and CMM on the ET promotion and electrocatalytic activity.Based on Pt-CMM nanocomposite film,the quasi-reversible electron transfer for GOx is probed and the apparent heterogeneous electron transfer rate constant(ket0) is 6.5 s-1,lager than 3.9 s-1 based on pure CMM. In addition,the associated biocatalytic activity is revealed.The prepared biosensor offers a more stable and sensitive amperometric detection of glucose with a lower detection limit under the optimal Pt/CMM weight ratio of 5 wt.%.Considering the high cost and resource consumption when doping noble metal nanopaticles,we focused on the deep study in the mesostructure adjustment in the following work.In Chapter Three,we investigate the electrochemistry and biosensing of GOx based on CMMs with different spatially-ordered dimensions.As discussed in Chapter Two,the CMM composite matrix is provided with both the ideal immobilization ability for enzymes and the biocompatible microenvironment for preserving the bioactivity of enzyme molecules.Meanwhile,due to their inherent good conductivity, the CMMs can promote the electron communication between the immobilized enzyme molecules and the underlying electrode,realizing fast electron transfer between the enzymes and the modified electrode surface.Thus we designed and prepared highly ordered two-dimensional(2D-) and three-dimensional(3D-) CMMs to immobilize GOx.The quasi-reversible ET of the redox enzyme is probed,and the apparent heterogeneous electron transfer rate constants(ket0) are 3.9 and 4.2 s-1 respectively.Furthermore,the associated biocatalytic activity was also revealed. Highly ordered 3D-CMM exhibited larger adsorption capacity for proteins and the immobilized enzymes retained a higher bioactivity compared with 2D-CMM.The mediated glucose biosensor based on 3D-CMM showed a high sensitivity,broad linear response range,and low detection limit.In Chapter Four,we studied the electrochemistry and biosensing of proteins based on bicontinuous gyroidal mesoporous carbon(BGMC).Because 2D-CMM has a disordered dimension,resulting in its conductivity anisotropy higher than that of 3D-CMM,3D-CMM exhibits a higher apparent conductivity than 2D-CMM. However,such enhancing degree is not very ideal.Because some silica templates of 3D-CMM,such as MCM-48 and FDU-5,are lack of interconnected micropores,the partial displacement of the carbon frameworks occurs after the removal of the silica template,leading to the decrease in spatial symmetry and simultaneously the increase in the conductivity amsotropy.Thus the above carbon matrixes are limited in achieving a considerably ideal promotion of ET between redox proteins and electrodes.While BGMC has a more ordered mesoscopic structure with the higher symmetry of 3D-Ia(?)d,possessing a relatively isotropic graphited structure and thus can more effectively enhance the heterogeneous electron communication.Herein a strategy was demonstrated,of the preparation of protein-entrapped BGMC nanocomposite films for assembling redox proteins(employed glucose oxidase and myoglobin as the models).The immobilized proteins showed fast electrochemistry and retained their bioactivity to a certain extent.In addition,a series of BGMCs with different pore sizes from 2 to 7 nm was designed and synthesized with sucrose or phenol formaldehyde(PF) resin as a carbon source.Pore sizes and carbon sources show great influences on the immobilization of redox proteins and on the ET between redox proteins and electrodes.It means that the pore diameter and structural topologies can be readily tuned to match the dimensional size of diverse biomolecules, to promote heterogeneous ET and to enhance the electrocatalytic properties of the proteins.All these properties make BGMC valuable in the understanding on the electrochemistry of redox proteins and expand the scope of carbon-based electrochemical devices.In Chapter Five,we studied the electrocatalytic oxidation of NADH based on BGMC with low overpotential.To the best of our knowledge,no previous work has been reported on the direct electro-oxidation research of NADH based on 3D-CMM. Herein we used the BGMC-modified electrode to study the electrochemical oxidation of NADH.The large specific surface area and the high electron-communicating capability of BGMC,plus the considerable edge-plane-like defective sites and the oxygen-containing groups on the BGMC surface could be responsible for its electrocatalytic behavior,which induced a substantial decrease by 649 mV in the overpotential of NADH oxidation reaction(compared with a bare electrode).The BGMC-modified electrode offers a stable and sensitive amperometric detection of NADH at a low overpotential(+0.046 V vs.SCE,pH 7.2) with a low detection limit (1.0×10-6 M) and a broad linear response range(3.0×10-6~1.4×10-3 M).This might broaden the development avenue of amperometric biosensors based on NADH-dependent dehydrogenase.In Chapter Six,we summarized and pointed out the shortcomings in this dissertation.Finally we proposed the objects and schemes of further research.
Keywords/Search Tags:Mesoporous carbon, Chemically modified electrodes, Electron transfer, Protein, Glucose oxidase, Myoglobin, NADH, Electrochemistry, Biosensor
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