The Preparation Of Nanotube Composite And Its Application For Biosensors

The integration of nanomaterials with biological systems is an attractive research area of nanobiotechnology.The construction of functional hybrid systems that incorporate the highly selective catalytic and recognition properties of biomolecules with the unique electronic,photonic,and catalytic features of nanomaterials are of great importance for potential applications in nanoelectronic devices and biosensors. As a new type of carbon nanomaterial,carbon nanotubes(CNTs)have been the focus of intensive study due to their excellent physical and chemical properties since their discovery by Iijima in 1991.They are considered as promising building blocks for the construction of novel biosensors because of their high surface area,good biocompatibility and rich electronic properties.Now numerous CNTs-based biosensors have been developed with a variety of enzymes.In most case,CNTs modified electrodes have been prepared by drop costing method.However,the insufficient reactivity and stability of such modified electrodes seem to impede their applications.To overcome these problems and exploit the potential applications in future biosensors and nanodevices,it is necessary to develop versatile reliable approaches to assemble or integrate CNTs onto solid surfaces.Recently,composite materials based on integration of CNTs and some other materials have gained growing interest.Although some creative efforts on the construction of the CNTs-based electrodes have almost been made,with the further development of CNTs and nanotechnology,the study on the preparation,properties and application of CNTs and its composite materials is still a hot topic attracting lots of researchers in the world.This thesis is divided into seven chapters and the details are given as follows:In chapter 1,we present the systemic overview on the development of CNTs.The preparation of CNTs,the functionalization of CNTs and its application are described in detail.In chapter 2,an electrochemical sensing platform was developed based on the magnetic loading of CNTs/Fe₃O₄ composite on electrodes.To demonstrate the concept,Fe₃O₄ was deposited by the chemical coprecipitation of Fe²⁺and Fe³⁺in the presence of CNTs in an alkaline solution.The resulting magnetic nanocomposite brings new capabilities for electrochemical devices by combining the advantages of CNTs and Fe₃O₄ and provides an alternative way for loading CNTs on electrodes. The fabrication and the performances of the magnetic nanocomposite modified electrodes have been described.The marked electrocatalytic activity toward hydrogen peroxide permits effective low-potential amperometric biosensing of glucose.The concept of the magnetic loading of CNTs nanocomposite has great promise for creating CNTs-based biosensing devices and expands the scope of CNTs-based electrochemical devices.In chapter 3,the multi-walled carbon nanotubes(MWNTs)filled withγ-Fe₂O₃ nanoparticles have been prepared via hydrothermal reaction of shortened MWNTs in ferric nitrate solution and subsequent calcinations.Magnetic nanoparticles have been introduced into MWNTs via wet chemical method.The resulting products were characterized by TEM,EDX,XRD,XPS,and VSM.The prepared magnetic MWNTs (M-MWNTs)can be well dispersed in the water and can be easily magnetic separated from the medium.The adsorption test demonstrates that it is a superior absorbent for the removal of dyes(NR and MB).Compared with other absorbents,the M-MWNTs not only have high adsorption efficiency to dyes,but also can be easily manipulated by external magnetic field.The combination of the superior adsorption properties of MWNTs and the magnetic properties of Fe₂O₃ nanoparticles makes it became a powerful separation tool to deal with environmental pollution.In chapter 4,a new type of electrochemical nanostructured biosensor based on CNTs has been constructed by magnetic assembly method.The multilayered functional platform could be assembled using M-MWNTs and enzyme with the aid of magnetic field.The Horseradish Peroxidase(HRP)was employed as a model enzyme to demonstrate the final performance of the nanostructured biosensor.SEM,UV-vis spectroscopy and electrochemical techniques were used for characterization of assembly process.The resulting three-dimensional M-MWNTs/HRP multilayer films have showed satisfactory stability,biocompatibility and electrochemical properties. The results showed that the magnetic assembly method enhanced the density of CNTs and the amount of enzyme loaded on the electrode,leading to the improvement of the behavior of the biosensor.Our present study may provide a general way to the construction of nanostructure biofunctional surfaces of carbon nanotubes in a highly controllable manner,while integrating the highly catalytic properties of biomolecules.In chapter 5,a nanobiocomposite film consisted of zirconia,MWNTs and Myoglobin(Mb)was electrochemically deposited on the electrode.Mb immobilized in the film has realized direct electrochemistry and kept high electrocatalytic efficiency toward H₂O₂.The proposed biosensor via a simple one-step electrodeposition method displayed a broader linear range and a lower detection limit for H₂O₂,as compared with those CNTs or ZrO₂ based biosensor.The present strategy provides a simple and effective method to assemble CNTs,ZrO₂ and enzyme nanohybrid on the electrode and can be application to the other biosystems.In chapter 6,direct electrochemistry of hemoglobin(Hb)at silicate nanotubes(SNT) modified electrode was studied.Firstly,this hybrid silicate nanotube was prepared by a hydrothermal process in a mixed water/ethanol solvent system.This opened nanotube has homogeneous diameter and its surface is hydrophilic.The resulting products were characterized by TEM,EDX,and XRD.Then the SNT coated electrode was prepared and the film was characterized by SEM and electrochemical impedance spectroscopy(EIS).Hb at SNT electrode has realized direct electrochemistry and kept high electrocatalytic efficiency toward H_O2.It could be anticipated that the SNT modified electrode could be used in biosensors and biofuel cells.Chapter 7 is the summary of this thesis.Meanwhile,the direction of related research is also proposed.