Preparation Of TiO₂ Nanocomposites And Their Application In Photoelectrochemical Biosensors

As a newly developed analysis technique,photoelectrochemical?PEC?biosensors have combined the advantages of optical methods and electrochemical methods,and exhibited high sensitivity,rapid response,inexpensive apparatus and simpleness.Before the construcution of the PEC sensors,the development of photocatalytic semiconductor nanomaterials is critical to the performance of biosensors.Among the various photoactive materials,TiO₂ is an ideal and typical photoactive material to fabricate PEC sensors due to its strong photocatalytic activity,good stability,nontoxicity,controllable morphology and excellent biocompatibility.However,the wide band gap of TiO₂?3.2 e V?limits its absorption in the visible region and the photogenerated electron-hole pairs are subjected to fast recombination.To minimize these drawbacks,many narrow band gap semiconductors materials have been combined with TiO₂ to form the composites with the enhanced visible light absorption and electronic transfer to improve its PEC performance.In this work,various semiconductor materials sush as g-C₃N₄,BiVO₄,MoS₂ and noble metal Au NPs combined with TiO₂ respectively,which were designed as the photoactive substrates to immobilize the biomolecules for PEC bioanalysis.The main contents are listed as follows:1.A photoelectrochemical enzyme biosensor based on g-C₃N₄-TiO₂ nancomposite for detection of glucose.In this chapter,we reported a novel photoelectrochemical enzyme sensor with a g-C₃N₄-TiO₂ nanocomposite as the scaffold for detection of glucose.Initially,the pure g-C₃N₄ were synthesised by pyrolysis of tripolycyanamide powder.Then,the g-C₃N₄-TiO₂ nanocomposite was prepared using a solvothermal method with TTIP as titanium source and g-C₃N₄ as the substrate,on which TiO₂ nanosheets were tightly deposited.The structure and performance of prepared samples were characterized by the various techniques.The PEC GOx biosensor was then prepared with g-C₃N₄-TiO₂ nanocomposite as sensor scaffold and Nafion as a binder to immobilize GOx on the ITO electrode.Finally,this PEC biosensor was researched by PEC method and applied to detecct glucose.2.A photoelectrochemical aptasensor based on TiO₂-BiVO₄ nancomposite for detection of 17?-estradiol.In this section,TiO₂-BiVO₄ was employed as a nanostructured support to cross-link DNA aptamer for constructing a visible-light driven PEC aptasensor,which was used for detecction of 17?-estradiol?E2?.Initially,the monoclinic BiVO₄ were prepared by chemical precipitation and calcination method with Bi?NO3?3·5H2O and NH4VO3 as raw meterials.The precursor TiO₂ spheres were synthesized using a sol-gel method with TTIP as titanium source.Secondly,the TiO₂-BiVO₄ nanocomposite and anatase TiO₂ spheres were obtained by the solvothermal method.Various techniques have been applied to characterize the structure and performance of these nanomaterials.After that,the TiO₂-BiVO₄ nanocomposite was assembled on the ITO eletrode,and then the aptamer of E2 was immobilized onto the electrode with glutaraldehyde as cross-linker to obtain the PEC aptasensor.Finally,the proposed PEC proposed aptasensor showed excellent analytical performance with E2 as an analyst model.3.A photoelectrochemical aptasensor based on TiO₂-MoS₂-Au NPs nancomposite for detection of kanamycin.In this paper,we reported the development of a PEC aptasensor consisting of a novel TiO₂-MoS₂-Au NPs flower-like nanocomposite using kanamycin as a model analyte.We have firstly synthesised mesoporous TiO₂ microspheres with a large and rough surface by sol-gel and solvothermal method with TTIP as titanium source.MoS₂ flakes were synthesized using TiO₂ microspheres as the substrates to form TiO₂-MoS₂3D flower-like nanocomposite and then Au NPs were deliberately decorated on the surface of the TiO₂-MoS₂ nanocomposite with a routine chemical reduction method to produce the ternary nanocomposite.These nanomaterials were characterized by the same techniques as above.The TiO₂-MoS₂-Au NPs nanocomposite was demonstrated to accelerate the electron transfer,increase the loading of aptamers and improve the visible light excitation of the sensor.Finally,SH-functionalised kanamycin aptamers as a recognition unit were immobilised on the modified electrode to develop an aptasensor for kanamycin.