Preparation Of TiO₂ Nanocomposites And Their Application In Electrochemical /Photoelectrochemical Biosensors

Because of the inherent advantages of high chemical stability,excellent biocompatibility,large specific surface area,non-toxicity,easy preparation and tunable size,TiO₂ nanomaterials have attracted special attention and are widely applied in the construction of electrochemical and photoelectrochemical biosensors.However,TiO₂ nanomaterials have also suffered from some disadvantages including poor electron conductivity,large band gap leading to the sole absorption of UV excitation light,and rapid recombination of photogenerated electron-hole pairs,which greatly limited their application in the field of biosensors.In order to minimize these shortcomings,many modification methods including atoms doping,composite materials,and semiconductor coupling have been applied in the amelioration of TiO₂ for the enhance of the biosensor performance.In this work,different morphologies of one-dimensional TiO₂nanomaterials have been synthesized with the facile hydrothermal methods,and were then composited with polyaniline?PANI?,gold nanoparticles?AuNPs?,and molybdenum disulfide?MoS₂?nanomaterials respectively to form different TiO₂ nanocomposites.These TiO₂ nanocomposites were used as the scaffolds of electrochemical immunosensor and photoelectrochemical enzyme sensors to immobilize biomolecules for the electrochemical detection.The main contents are listed as follows:1.Construction of electrochemical immunosensor using TNT-PANI-AuNPs nanocomposite as oriented immobilization scaffoldInitially,TiO₂ nanotubes?TNTs?were synthesized with TiO₂ nanoparticles as raw material using a facile hydrothermal method.Then,PANI was coated on TNTs with aniline as precursor by chemical oxidative polymerization to form TNT-PANI nanocomposite.After that,gold nanoparticles?AuNPs?were deposited on TNT-PANI with a routine chemical reduction and TNT-PANI-AuNPs nanocomposite was prepared successfully.Various testing techniques have been applied to characterize these nanomaterials.With chitosan solution as dispersant,the ternary nanocomposite was applied as the scaffold of electrochemical immunosensor.Using bis?sulfosuccinimidyl?suberate?BS³?as amino cross-linker,the TNT composite could be further functionalized with protein G?for oriented immobilization of capture antibody on the electrode surface.Finally,the immunosensor was assembled and applied for the quantitative detection of analytes.Using?-fetoprotein?AFP?as an analyte model,the immunosensor showed a linear range of 0.01-350 ng mL^-1 with a detection limit of 1.5 pg mL^-1.2.Construction of electrochemical immunosensor based on TiO₂ nanowire arrays?TiNWs?modified with a simultaneous“etching,doping and deposition”techniqueInitially,dense and orderly TiNWs were prepared with FTO as substrate and tetrabutyl titanate as titanium source.After a simultaneous“etching,doping and deposition”modification technique,Mo element was effectively doped in the TiNWs and MoS₂ flakes were successfully deposited on the surface of electrode.The triply modified TiNWs have provided a biocompatible platform with high specific surface area to immobilize the large amount of antibodies and improved the electron transfer of TiNWs.Various testing techniques have been applied to characterize the nanomaterial.The triply modified TiNWs were used as the scaffold of electrochemical immunosensor.With the aid of double amino-reactive crosslinker-bis?sulfosuccinimidyl?suberate?BS³?,capture antibodies were immobilized on the scaffold surface for the quantitative detection of analytes.Using carcinoembryonic antigen?CEA?as a model analyte,this amperometric method showed a linear range of 0.001-150 ng mL^-1 with a detection limit of 0.5 pg mL^-1.3.Construction of glucose oxidase?GOx?photoelectrochemical sensor based on TiO₂nanorods-MoS₂ flakes?TiO₂-MoS₂?heterostructure scaffoldCylindrical TiO₂ nanorods were initially prepared using a hydrothermal method with TiCl₄ as titanium source,and then MoS₂ flakes were synthesized using TiO₂ nanorods as the substrates to form TiO₂-MoS₂heterostructure to enhance the photoelectric property.Various testing techniques have been applied to characterize these nanomaterials.The GOx photoelectrochemical biosensor was prepared with TiO₂-MoS₂heterostructure as sensor scaffold to immobilize GOx.The bioactivity of GOx to glucose was validated with cyclic voltammetry in O₂-saturated PBS solution.The photoelectric property of the nanomaterials and the quantitative detection of glucose were all conducted through current-time?I-T?curve method.The photoelectrochemical biosensor exhibited a dynamic range of 0.1-10.5 mM,sensitivity of 0.81?A mM^-1,and a detection limit of 0.015 mM within the visible spectrum.