Preparation Of TiO₂-Polyaniline Nanocomposites And Their Application In Electrochemical And Photoelectrochemical Biosensors

Because of the high sensitivity, good stability, easy operation, low cost and online monitoring in a complex environment, electrochemical sensors have been widely applied in the field of environmental protection, clinical, industrial and agricultural production. Through combining the advantages of the photochemical and electrochemical biosensors, the photoelectrochemistry biosensors have exihibed rapid response, high sensitivity and low cost characteristics in life science, medicine, environmental monitoring,food safety and other fields. Nanomaterials have displayed some unique physical and chemical properties,catalytic activity and good biocompatibility due to their surface effect, volume effect, quantum size effect and macroscopic quantum tunneling effect. Therefore, various nanomaterials are frequently used to construct biosensors in reeent years. Especially, TiO₂ nanotubes become a hot spot in the research of biosensors owing to its large specific surface area, excellent optical response, excellent chemical stability,good biocompatibility and one dimensional electron transport structure. In addition, the excellent electrical conductivity of polyaniline?PANI? can inhibit the recombination of the electron hole pair of the nano semiconductors such as TiO₂ and thus significantly improve the photoelectric chemical activity of these materials. In our work, TiO₂ nanotubes?TNTs? were initially synthesized through hydrothermal method,and a variety of TiO₂ nanocomposite materials were then synthesized using different methods. Finally, the TiO₂ nanocomposite materials were used as carriers to embed enzymes for the devopment of new type of electrochemical and photoelectrochemical sensors. The main contents are as follows:1. Preparation of polyaniline-TiO₂ nanotube composite for the development of glucose oxidase electrochemical biosensorUsing a hydrothermal method, TiO₂ nanoparticles were initially transformed into TNTs, on which aniline was then polymerized by oxidative polymerization to form an intimate and uniform PANI–TNT composite. After being characterized by different spectroscopic techniques, the PANI–TNT composite was used to immobilize glucose oxidase?GOD? for the construction of an electrochemical biosensor. The direct electrochemistry and electro-catalytic performance of the biosensors based on PANI–TNTs and TNTs was studied by cyclic voltammetry. The direct electrochemistry of GOD on PANI–TNTs modi?ed electrodeswas achieved and the heterogeneous electron transfer rate constant?Ks? for GOD was estimated to be 9.3 s-1.The PANI–TNT modi?ed GOD biosensor exhibited good sensitivity?11.4 ?A mM-1?, wide dynamic range?10–2500 ?M? and low limit of detection?0.5?M?.2. An intimately bonded titanate nanotube-polyaniline-gold nanoparticle ternary composite as a scaffold for the development of horseradish peroxidase electrochemical biosensorThe scaffold was constructed by oxidatively polymerising aniline to produce an emeraldine salt of PANI on TNTs, followed by gold nanoparticle deposition. A novel aspect of this scaffold lies in the use of the emeraldine salt of PANI as a molecular wire between TNTs and GNPs. Using horseradish peroxidase?HRP? as a model enzyme, voltammetric results demonstrated that direct electron transfer of HRP was achieved at both TNT-PANI and TNT-PANI-GNPs-modi?ed electrodes. Based on chronoamperometric detection of H2O2, a linear range from 1 to 1200 ?M, a sensitivity of 22.7 ?A mM-1and a detection limit of0.13 ?M were obtained at the TNT-PANI-GNPs-modi?ed electrode.3. Gold nanoparticles deposited polyaniline-TiO₂ nanotube for surface plasmon resonance enhanced lactate dehydrogenase photoelectrochemical biosensingPANI was initially coated on TiO₂ nanotube with an oxidative polymerization method, and12-phosphotungstic acid was then used as a highly localized photoactive reducing agent to deposit GNPs on TNT-PANI. The morphology and composition of the composite were characterized by various spectroscopic and microscopic methods. Electrochemical impedance spectroscopy was also conducted to demonstrate the excellent electrical conductivity of the composite. A PEC biosensor was fabricated by immobilizing a mixture of lactate dehydrogenase and the composite onto ITO electrodes, which regenerated nicotinamide adenine dinucleotide?NAD+? to complete the enzymatic cycle and led to an improved method for PEC detection of lactate. Because of the surface plasmon resonance enhanced effect of GNPs, the electrochromic performance of PANI, and excellent conductivity and biocompatibility of the composite, this method showed a dynamic range of 0.5-210 ?M, sensitivity of 0.0401 ?A ?M-1, and a detection limit of 0.15 ?M.