Preparation Of Nanowires And Composite Film Based On Carbon Nanotubes For The Construction Of Electrochemical Biosensing Platform

Electrochemical biosensors based on the specific recognition of biomaterials and the magnification function of electrochemical determination have some outsanding advantages including high sensitivity, nice selectivity, low cost as well as easy miniaturization and automation. They have potential applications in environmental monitoring, clinical diagnosis, chemical measurements in the agriculture, food industry. In recent years, tremendous attention has been paid to develop new technologies and materials for the design and fabrication of electrochemical biosensors.Nanomaterials as new material have been widely researched and used because of their novel optical, electrical, catalytic properties and favorable biocompatibility. With the introduction of nanomaterials, the performance of biosensor has a greatly improvement. In this paper, we prepared some nanomaterials with different morphology, applying them to the fabrication of biosensors. The modified electrodes can be used to determine hydrogen peroxide in low potential with high sensitivity, ideal for the construction of biosening platform. Immobilizing glucose oxidase onto the platform, the resulting biosensors have high sensitivity, low detection limit and fast response time. The details are summarized as follows:(1) In chapter 2, poly-thionine nanowire/HRP/nano-Au composite nanomaterial was developed to fabricate the H₂O₂ biosensor. Poly-thionine nanowires (PTHNWs) have been synthesized by electrodeposition in porous anodic aluminum oxide (AAO) template. The nanowires prepared by this method can be used to encapsulate horseradish peroxidase (HRP) and nano-Au by in situ electrochemical copolymerization. The resulting PTHNWs-HRP-nano Au material facilitates electron-transfer process in electrochemical sensor design. The PTHNWs-HRP-nano Au film modified electrode showed to be excellent amperometric sensors for H₂O₂. In pH 6.98 phosphate buffer, almost interference-free determination of H₂O₂ is realized at -0.1V with a linear range of 5×10^-7 to 1.3×10^-2M, a correlation coefficient of 0.998 and response time <5s. The sensitivity of the H₂O₂ biosensor is up to 168μA mM^-1 cm^-2 and the detection limit is 0.3μM. Furthermore, the biosensor exhibited long-term stability, and good reproducibility.(2) In chapter 3, a new glucose biosensor was constructed based on prussian blue nanowire array (PBNWA), synthesized via electrochemical deposition with polycarbonate template. The electrocatalytic activity of the PBNWA toward hydrogen peroxide was investigated. The nanowire array can directly respond to hydrogen peroxide at low potential of -0.1V with high sensitivity and wide linear range. The nanowire array can improve the signal-to-noise ratio so as to reduce the detection limit, and the upper detection limit was increased because the high surface area of the nanowire array increased the amount of electroactive sites. A biosensor toward glucose was then constructed by crosslinking glucose oxidase onto the ordered nanowire array. The biosensor allowed rapid, selective and sensitive determination of glucose at -0.1V with a linear range of 2×10^-6-1×10^-2M, the detection limit of 1μM.(3) In previous study, we immobilized glucose oxidase onto the surface of electrode using the cross-linking with glutaraldehyde, and it can lead to denature of enzyme. The performance of biosensor needed to be improved. In chapter 4, prussian blue/Pt composite nanowire array was synthesized by electrodeposition in polycarbonate membrane with aim to immobilize enzyme onto the nanowire array via electrodeposition. The electrochemical behavior and electrocatalytic activity toward H₂O₂ of the composite nanowire array were investigated. As seen from the TEM image of prussian blue/Pt composite nanowire, the composite nanowire easily ruptured because of the weak acting force between prussian blue and Pt. As a result, the response to H₂O₂ was unstable. The acting force was ignored and the experiment result was unideal. This method needs to be improved.(4) In chapter 5, platinum nanoparticle-loaded chitosan is prepared and combined with TEOS sol-gel solution, multiwalled carbon nanotubes (MWNTs) are then dispersed into the composite matrix. The MWNTs and nano-sized Pt (NSPt) composite material brings new capabilities for electrochemical device by combining the advantages of MWNTs and NSPt as well as the sol-gel organic-inorganic technology. The CNTs-NSPt composite modified glassy carbon electrode has favorable electrochemical behavior to H₂O₂. As an application example, the glucose oxidase was immobilized onto the surface of modified electrode through cross-linking by glutaric diadehyde. The resulting glucose biosensor exhibited a short response time (<5s), with a linear range of 0.05-8mM and detection limit of 10μM.