Construction Of CdS-based Photoelectrochemical Sensors And Their Application In MicroRNA And Small Molecule Assays

Photoelectrochemical（PEC）sensing analysis is a kind of analysis method based on the principle of photoelectrochemistry which outputs the information of the detected object in the form of electrical signal in the presence of light source.Because the input energy and the output signal are different,it has the advantages of low background signal naturally.In addition,it also has many advantages such as high sensitivity of traditional electrochemistry and the instrument is easy to operate.Photoelectrochemical active materials,as the medium of conversion between light energy and electric energy and between electric energy and chemical energy in PEC process,have always attracted a lot of attention.CdS,as a kind of semiconductor photoelectric material with appropriate band gap,can be combined with other semiconductor materials to build a built-in electric field and improve the carrier separation efficiency of narrow band gap materials.On the other hand,as a photosensitizer,CdS can improve the light response ability of other broad band gap materials and effectively reduce the light corrosion.In addition,nucleic acid molecules or some small molecules are closely related to human diseases or food safety,so it is of great significance to develop the corresponding sensitive and convenient photoelectric sensing platform.Based on the problems of low photoelectric conversion efficiency and easy photocorrosion of photoelectric active materials,this paper carried out the work in the following three aspects:1.MicroRNAs（miR）as the newly identified biomarkers are closely associated with various cancers,and sensitive monitoring of abnormal miR is great importance in cancer diagnosis and treatment of diseases.In this work,a signal-off photoelectrochemical biosensor was constructed to sensitively detect miR-141 by competitive dual-quenching of CHA-dependent Cu2O NCs toward β-CD@CdS NRs.The biosensing platform was constructed by stepwise assembly of β-CD@CdS NRs and ADA-H1 on ITO electrode surface.In the presence of miR-141,CHA recycling was trigger to immobilize the capture DNA-labeled Cu2O NCs with the aid of hairpin DNA probe 2.The assembly of Cu2O NCs could largely reduce the photocurrent response of CdS NRs based on the competitive consumption of light energy and electron donor（AA）.The designed biosensor showed a wide linear range（1.0×10-12 M-1.0×10-7 M）and a detection limit of 4.7×10-13 M,as well as excellent selectivity and satisfactory stability.Based on the above outcomes,the proposed biosensing devices was also applied to miR-141 analysis in human serum,achieving great prospect in clinical application.2.Core-shell MoS2@CdS nanorods heterojunction photoelectrochemical materials（MoS2@CdS NRs）were synthesized by rehydrothermal method using CdS NRs synthesized in Part I as the core.The peroxidase-like activity of MoS2@CdS NRs was explained by ultraviolet detection experiment,and then,it uses its analog enzyme properties to catalyze H2O2 generated during the decomposition of glucose by glucose oxidase,so that 4-chloro1-naphthol（4-CN）in the solution is converted into insoluble precipitation on the electrode surface,thus reducing the photocurrent signal of the system,so that the glucose concentration information can be converted into photoelectric signal output.Finally,the photoelectric chemical detection of glucose was realized.The detection range of the sensor is 1.0×10-4 M-1.0 M.and the detection limit is 4.6×10-5 M.3.Firstly,ZnO nanorods（ZnO NRs）were prepared by high temperature calcination.Then,CdS was coated on ZnO NRs by liquid phase synthesis method to obtain core-shell CdS@ZnO nanorods heterojunction photoactive materials（CdS@ZnO NRs）.By comparing the photocurrent of CdS@ZnO NRs with ZnO NRs.the photocurrent of CdS@ZnO NRs is about 7.4 times larger than that of ZnO NRs,indicating that the existence of CdS affects the photocurrent of CdS@ZnO NRs in a large proportion.It is worth noting that nitrite can etch CdS.Based on this,we designed the nitrite photoelectrochemical sensing platform.In the presence of nitrite,nitrite can interact with the S2-ion of CdS,so the CdS on CdS@ZnO NRs surface is etched,thus affecting the photocurrent of electrode modified by CdS@ZnO NRs to achieve the purpose of detecting nitrite.The detection range of sodium nitrite by this sensor is 1.0×10-8 M-1.0×10-4 M,and the detection limit reached 4.0×10-9 M.And has good stability and selectivity.