Photoelectrochemical Immunoassay Based On Cadmium Sulfide Quantum Dots And Enzyme/mimetic Enzyme-mediated Catalytic Reaction

Photoelectrochemical（PEC）immunoassay,as an emerging analytical method,has been widely used in the monitoring of various proteins and tumor markers due to their high sensitivity,low backgroud and high specificity,which stems from desirble immunological recognition and complete separation of excitation light and photoelectrochemical signal.However,comparied to electrochemical and fluorescent techniques,PEC immunoassay study is still in the early stage,and confronted several limitations such as complicated modification steps,unsatisfactory light-electricity conversion and stability of photoactive materials.To solve these problems,three interesting works were designed as follows:1.Based on enzymatic biocatalytic precipitation to quench the amplified photocurrent response that generated from WS2 nanosheets sensitized CdS quantum dots heterostructure,a novel photoelectrochemical immunosensor was constructed for sensitive alpha-fetoprotein（AFP）monitoring,in which anti-AFP antibody and horseradish peroxidase-tagged anti-AFP antibody（HRP-Ab2）served as capture unit and signal indicator,respectively.In the presence of AFP,HRP-Ab₂ was immobilized on electrode surface for establishing sandwich-type immunocomplex via antigen-antibody interaction,and subsequently catalyzed 4-chloro-l-naphthol to form the nonconductive and insoluble precipitation,which effectively impeded the diffusion and electron transfer of electron donor,achieving the decreased photocurrent.Under optimized conditions,the excellent linearity range（1 pg mL-1-20 ng mL-1）,satisfactory detection limit（0.43 pg mL-1）,desirable selectivity and good stability were obtained for designed immunosensor.Moreover,the application of AFP determination in human serum allowed it to hold great potential for early diagnostics of some cancer diseases.2.A novel PEC immunosensor was designed for ultrasensitive monitoring of prostate specific antigen（PSA）based on Cu2+-mediated catalytic reaction for inhibiting the in situ generation of CdS quantum dots（QDs）coupled with the enhancement effect of CdS/MoS2 heterojunction,which was constructed by the stepwise modification of MoS2 QDs and CdS QDs on ITO electrode surface.In the presence of PSA,CuO NPs-labeled anti-PSA antibody was immobilized onto anti-PSA antibody modified 96-well plate via sandwich immunoreaction,and dissolved by hydrochloric acid to obtain a large number of Cu2+.As Cu2+-triggered catalytic oxidization of glutathione occurred,in situ growth of CdS QDs was significantly suppressed,resulting in the reduction of photocurrent response.Under optimal conditions,the biosensor exhibited the desirable linearity in the range from 0.5 pg mL-1 to 10 ng mL-1,low detection limit of 0.29 pg mL-1,satisfactory selectivity,good stability,and was applied to PSA detection in human serum,holding great potential for early diagnostics of some cancer diseases.3.An ultrasensitive split-type photoelectrochemical immunosensor was constructed to detect carcinoembryonic antigen（CEA）based on the inhibition of in situ generated CdS quantum dots（QDs）by the catalytic oxidation of hybrid chain reaction（HCR）-programmed dsDNA@hemin complex.In the presence of CEA,biotin-labeled anti-CEA antibody was introduced onto anti-CEA modified 96-well plate by sandwich immunological reaction,followed by the immbilization of biotin-labled DNA probe in the aid of biotin-streptavidin linkage,which could futher innitiate the HCR process to form long double-stranded DNA.Then,dsDNA@hemin complexes were generated after the convenient assembly of hemin molecules into dsDNA scaffold though groove interaction,and catalyzed the oxidation of glutathione to suprress the formation of CdS QDs,resulting in the reduction of photocurrent response.Under optimal conditions,the biosensor had desirable linearity in the range from 1 pg ml-1 to 10 ng mL-1,satisfactory detection limit of 0.66 pg mL-1,high selectivity and stability.Moreover,the detection of CEA in human serum exhibited acceptable accuracy and repeatability,providing broad application prospects in the early diagnosis of certain cancer diseases.