Preparation Of TiO₂ Heterojunction Nanostructures And Their Application In Electrochemical/Photoelectrochemical Aptasensors

The outstanding advantages of TiO₂ nanomaterials have made it widely used in various fields.However,some disadvantages of TiO₂ including the poor electrical conductivity,low separation efficiency of photogenerated charges and sole absorption of UV light have limited its futher application.To improve the application of TiO₂ in the various fields,it is necessary to modify TiO₂ by some methods.In this work,different TiO₂ nanocomposites were synthesized to minimize the shortcomings,and the composites were applied for the construction of electrochemical and photoelectrochemical biosensors.The synergistic interaction between metal sulfide and TiO₂ nanomaterials including nanorods,nanospheres and nanocubes,will benefit the performance of biosensors based on the nanocomposites.The main contents are listed as follows:1.Fabrication of electrochemical aptasensor using MoS₂-TiO₂@Au nanocomposites as the sensor scaffold for detection of tetracyclineFirstly,the TiO₂ nanorods were grown on MoS₂ nanospheres by a facile hydrothermal method to form flower-like MoS₂-TiO₂ composites,which were then aminated.Following that,gold nanoparticles were deposited on the aminated MoS₂-TiO₂ to produce MoS₂-TiO₂@Au ternary composite which was used as scaffold of biosensor.The thiolated TET aptamer through Au-S bonds was immobilized on the glass carbon electrode modified by MoS₂-TiO₂@Au to construct an electrochemical aptasensor.The tetracycline aptamer could well hybridize to its complementary biotin-DNA oligonucleotide?bio-cDNA?and also specifically combine with TET?a competitive relation was formed between TET and bio-cDNA?.The avidin-horseradish peroxidase?avidin-HRP?could catalyse the conversion of hydroquinone?HQ?to benzoquinone?BQ?with the assistance of H₂O₂,which has significantly amplified the electrochemical detection signal and could apply for the quantitative determination of TET.2.A photoelectrochemical aptasensor constructed with core-shell CuS-TiO₂ heterostructure as the sensor scaffold for detection of microcystin-LRInitially,the smooth TiO₂ nanospheres were prepared by sol-gel method,which was then calcined at450°C for 2 h to obtain anatase TiO₂.Following that,CuS nanoparticles were deposited on the surface of spherical TiO₂ with a hydrothermal method to form CuS-TiO₂ heterostructure.The CuS-TiO₂nanocomposite was immobilized on ITO with chitosan film,the PEC aptasensor was fabricated by using glutaraldehyde as a linker to covalently bind corresponding aminated aptamer to chitosan film for the detection of MC-LR in environmental water samples.The composite also possesses a large specific surface,loading amount the biomolecules.At the same time,it delays the recombination of photo-generated charges,which enhanced the photo-to-current conversion efficiency.MC-LR captured by the aptamer on the aptasensor could be oxidized into the non-toxic and harmless small molecule by the photogenerated hole resulting in the separation of photogenerated charges and enhancing the photocurrent.3.A photoelectrochemical aptasensor for aflatoxin B1 detection based on an energy transfer strategy between Ce-TiO₂@MoSe₂ and Au nanoparticlesBriefly,Ce-TiO₂@MoSe₂ heterojunction was obtained by growing MoSe₂ nanosheets on a TiO₂nanocube doped by Ce element with a facile hydrothermal method,which was used as scaffold to load aflatoxin B1?AFB1?aptamer.Then,AuNPs-labeled DNA sequence was subsequently hybridized with the aptamer to fabricate a sandwich structure,which realized the resonance energy transfer?RET?between the Ce-TiO₂@MoSe₂ composite and AuNPs.After AFB1 was modified on the electrode,the sandwich structure was destroyed,which greatly weakened RET,leading to the increase of photocurrent.The energy resonance transfer become weaker attributed to the enhancement of AFB1 concentration,furthemore resulting in the amplication of photocurrent response.