Controllable Synthesis Of TiO₂ Functional Thin Films And Their Application In Photoelectrochemical Sensing

With the rapid development of economy,the material consumption of human beings has been greatly enriched.Meanwhile,the incidence of diabetes and other diseases closely related to blood glucose concentration is increasing,it is of practical significance to realize the effective and rapid detection of glucose concentration in blood and food.Photoelectrochemistry(PEC)biosensors have been widely regarded as a promising biochemical analysis method due to their low background signal,easy miniaturization and simple operation.The semiconductor photoelectrode plays a crutial role in determining the PEC biosensor performance,TiO₂,having the merits of appropriate band edge positions,low cost,excellent biocompatibility and stability,has been regarded a promising photoelectrode material for efficient PEC biosensors.However,its application in PEC sensors is still limited to some extent by its intrinsic features,e.i.large band gap(Rutile phase:3.0 e V,Anatase phase:3.2 e V),low carrier mobility,strong oxidation capacity of photo-holes and rapid charge recombination.In this thesis,effective strategies of crystal facet control,micro-morphology adjustment and heterostructure construction have been adopted to conquer the limiting features of TiO₂ and improve the performance of PEC biosensors based on the functional TiO₂ thin films,and high sensitivity PEC glucose biosensors have been constructed.The details are as follows:1)Controllable sythesis of TiO₂ thin films dominantly exposing{001}facets for the application of photoelectrochemical glucose biosensor{101}and{001}crystal facets of anatase TiO₂ have different atomic and electronic structures,photogenerated electrons and holes are selectively enriched on{101}and{001}crystal facets,respectively,exhibiting photogenerated charge spatial separation ability.Since the{001}crystal facet of anatase TiO₂ fully exposes five-coordinated unsaturated Ti atom,it is highly active and easy to form strong chemisorption with glucose oxidase,which is beneficial for the interface charge transfer.Therefore,the TiO₂functional film with exposing the highly active{001}crystal facet can achieve strong chemisorption of glucose oxidase on the photogenerated hole enriched area,which is favorable to bulid a photoelectrochemical biosensor device with high performance.In a typical process,an anatase phase TiO₂film with dominant exposure of{001}crystal facets was fabricated on the titanium foil by a hydrothermal method,then a PEC glucose biosensor was constructed based on it.The sensitivity of the linear response range from 0 3m M is 9.25?Am M^-1cm^-2,the detection limit is 0.179 m M(S/N=3).This work provides an important reference for the study of improving the performance of photoelectrochemical biodetectors based on the crystal facet engineering.2)Au nanopartical modified TiO₂ thin films dominantly exposing{001}crystal facets for the application of photoelectrochemical glucose biosensorTheoretical and experimental studies have shown that the performance of TiO₂-based sensors can be effectively improved by introducing sensitizers to extend the absorption range.Au nanoparticles,having visible light response surface plasmon resonance absorption and good biocompatibility for many biomasses,can be used as an efficient sensitizer to achieve good bioassay for many biomasses.Moreover,there is strong adsorption energy between Au nanoparticles and{001}facets of TiO₂,therefore Au nanopaorticles can be well adsorbed on{001}facets of TiO₂.In this chapter,we used a variety of methods to modify the Au nanoparticles as the sensitizer on the the TiO₂functional film dominantly exposing{001}facets.The strong interaction between the Au nanoparticles and the{001}facets of TiO₂ film enhances the ability of the photo-generated carrier separation and transfer across the interface,as well as the introduction of the Au nanoparticles increases the number of detection sites.Further more,the existence of{001}and{101}quasi-heterojunctions can achieve quick transfer of the sensitized electrons from the{001}facet to the{101}facet,reducing the recombination probability of photogenerated carriers.Subsquently,glucose oxidase was further decorated on above films for constructing the photoelectrode of the biosensor.Finally,a high performance with a satisfied sensitive of 16.97?A m M^-1 cm^-2,0-3 m M linear range with glucose detection limit(LOD))6.3?M(S/N=3)was obtained.The sensitivity is even higher than the other TiO₂-based photoelectrode systems with high specific surface area,demonstrating the advantage of crystal facet engineering in the direction of PEC biosensors.3)Constructing PEC glucose biosensor based on TiO₂@PDA core shell nanorod arraysThe one-dimensional single crystal nanorod array structure can realize the orthogonalization of the light incident direction and the carrier diffusion direction,and effectively promote the transport and separation of the photogenerated charge while ensuring sufficient light absorption,which is regarded as a kind of ideal structure of photoelectrode.Constructing one-dimensional core-shell heterostructure arrays can further enhance the light absorption and charge separation ability.Meanwhile,the shell layer can also act as a dispersant(and an intermediate layer)to inhibit the aggregation of active substances.In this section,we constructed a novel TiO₂@PDA(polydopamine)core-shell nanorod array photoelectric functional film,and established a stable and high sensitive PEC glucose biosensor.PDA as a p-type semiconductor has a suitable band edge position to construct type II heterostructure with TiO₂,Moreover,the surface hydroxyl group of TiO₂ and the PDA catechol group form a bridged bidentate bond by chelation,which can serve as a direct electron transfer channel between PDA and TiO₂.In addition,the PDA also stabilizes the biosensor performance by avoiding the decomposition of enzymes induced by the strong oxidizing holes from the TiO₂ core.A remarkable performance with an ultrahigh sensitivity of57.72?Am M^-1 cm^-2,0.2-1.0 m M linear range with a glucose detection limit of 0.0285 m M(S/N=3)and a high sensitivity of 8.75?A m M^-1 cm^-2 for a dynamic range of 1.0-6.0 m M were obtained in the glucose detection.This work might provide a strategy of constructing inorganic/organic core/shell structure with satisfactory PEC performance.