Transition Metal Sulphides Based Near-infrared Photoelectrochemical Biosensors

Photoelectrochemical（PEC）biosensing is a novel detection technique emerged recent years.PEC sensing systems possess many advantages including high sensitivity,low background signal and good selectivity,and have made great progress in biosensing applications.Semiconductor nanomaterials with excellent photoelectric activity play a crucial role in the construction of PEC sensing platforms.The selection of photoactive materials is closely related to the performance of biosensing platforms.In order to obtain superior photocurrent responses,photoactive materials with low electron-hole recombination should be selected for PEC biosensors fabrication.To improve sensing performances of photoelectrochemical immunosensors,many photosensitive nanomaterials such as nano-Ti O₂,nano-Zn O,and quantum dots including Zn S and Cd S QDs have been extensively investigated.However,due to possessing a wide bandgap,high-energy excitation sources（usually ultraviolet light）are commonly employed for exciting them to generate photocurrent.Unfortunately,a high-energy excitation source usually causes the deactivation of biorecognition elements immobilized on the sensing interface,resulting in poor selectivity,sensitivity and stability.Therefore,developing photosensitive materials that can be excited by low-energy excitation sources such as near-infrared light is desired for PEC immunosensor fabrication.In this dissertation,photoelectrochemical biosensors based on near-infrared photoelectroactive materials with excellent photoelectric conversion efficiency were developed.The main contents were detailed as following:（1）A visible and near-infrared light dual responsive photoelectrochemical aptasensor for prostate-specific antigenA visible and near-infrared light dual responsive“signal-off”and“signal-on”photoelectrochemical aptasensor was constructed for determining prostate-specific antigen（PSA）based on Mo S₂nanoflowers and gold nanobipyramids.The dual responsive photoelectrochemical aptasensor can provide accurate results for PSA determination.For the photoelectrochemical aptasensor fabrication,amino-group functionalized aptamers were immobilized on a Mo S₂nanoflowers modified glassy carbon electrode surface for the specific recognition,and thus to achieve a“signal-off”aptasensor for PSA under visible light illumination.Subsequently,gold nanobipyramids integrated with thiol-functional aptamer were introduced to the“signal-off”aptasensing interface after PSA recognition.Under excitation with near-infrared light at 808 nm,the photocurrent response can be amplified significantly due to the excellent conductivity and local surface plasmon resonance effect of gold nanobipyramids,thus to producing a“signal-on”model for determining PSA.Under the optimized conditions,the dual-responsive photoelectrochemical aptasensor shows a linear response to the logarithm of PSA concentration in the range of 0.005 ng m L^-1to 100 ng m L^-1.The detection limit for PSA determination with a“signal-off”or a“signal-on”mode is 1.75pg m L^-1and 0.39 pg m L^-1（S/N=3）,respectively.The dual-responsive photoelectrochemical aptasensor was also employed for determining PSA in clinical serum samples with satisfactory selectivity and excellent accuracy.（2）Au NRs@Ag₂S nanocomposites based cytosensor for Hep G2 cellsUsing gold nanorods as core and Ag₂S nanofilm as shell,an Au NRs@Ag₂S nanocomposite was successfully prepared.A near-infrared（NIR）photoexcited photoelectrochemical cytosensor was developed by using Au NRs@Ag₂S as photoactive element for detecting human hepatocellular carcinoma cells（Hep G2）.The TLS11a aptamer was immobilized on the Au NRs@Ag₂S core-shell nanocomposites surface by a classical coupling reaction between the-COOH group and the-NH₂group of the aptamer.The specific recognition of Hep G2 cells was accomplished by the interaction between the TLS11a aptamer and the overexpressed factors on the surface of Hep G2 cells.The binding of Hep G2 cells resulted in steric hindrance effects that cause the charge transfer resistance increasing and retard the transfer of electron donors to the electrode surface.Therefore,the photocurrent response decreased linearly with the cell concentration increasing.The cytosensor demonstrated excellent sensitivity,selectivity and biocompatibility to Hep G2 cells.The photocurrent variations were linearly correlated to the logarithm of Hep G2 concentrations from 1.0×10²cells m L^-1to 1.0×10⁶cells m L^-1,with a detection limit（S/N=3）of 26 cells m L^-1.