Preparation Of Metal Chalcogenide Quantum Dots And Their Application In The Photoelectric Detection Of Small Biological Molecules And DNA

Photoelectrochemical?PEC?bioanalysis as a newly emerging sensing technique,in which the input signal of light and the output signal of photocurrent are completely separated,has received considerable attention owing to the high sensitivity and low background signal.Semiconductor nanomaterials especially metal chalcogenide quantum dots,exhibit special PEC properties that are different from the bulk materials,such as quantum confinement effects,surface effects,etc.Enormous efforts have been expended to develop PEC devices with different properties,and present a trend of miniaturization and intelligence,which has great application value in the field of biological analysis.1.This work developed an enhanced photoelectrochemical biosensor for sensitive determination of glutathione?GSH?by means of the heterojunction effect of CdS/WS₂.The CdS/WS₂ photoanode was successfully constructed through the method of stepwise assembly,and achieved around 310%increase of photocurrent response in respect to CdS quantum dots?QDs?modified electrode due to the formation of heterostructure.Under illumination,with the photogenerated electrons of CdS QDs tended to WS₂ nanosheets and sequentially driven to ITO electrode,the corresponding photogenerated holes could continuously oxidize GSH into glutathione disulfide,inhibiting the recombination of electron-hole pairs,leading to a remarkable photocurrent change because of the efficient charge carrier separation.Under the optimized conditions,the biosensor demonstrated excellent sensing performances with the low applied bias potential of 0 V?vs Ag/AgCl?,as well as good stability,high selectivity,wide linear range from 20?M to 2.5 mM,desirable detection limit of 5.82?M.In addition,this biosensor has also been successfully utilized to the monitoring of GSH in human serum.2.A photoelectrochemical DNA sensor based on the triple signal amplification strategy of CdS/WS₂ heterojunction,hybrid chain reaction and enzyme catalysis was successfully constructed.The introduction of CdS/WS₂ heterostructure can not only greatly improve the photocurrent signal of the system,but also provide a good microenvironment for the fixation of probe DNA.In the presence of target DNA,the DNA probe has been immobilized on the surface of the electrode by DNA recognition reaction and initiates a hybridization chain reaction with the aid of auxiliary probe to form long double-stranded DNA structure with a large number of bio-H1 and bio-H2.Then,the alkaline phosphatase was assembled on the surface of the double-stranded DNA which based on the biotin-avidin interaction,and can catalyze the hydrolysis of trisodium L-ascorbic acid-2-phosphate in the electrolyte to produce ascorbic acid.The ascorbic acid acted as an electron donor,which can effectively inhibit the recombination of electron-hole pairs and produce a significant change in photocurrent,thereby greatly improving the sensitivity of the sensor and realizing the ultra-sensitive and specific detection of the target DNA.The biosensor has good sensing performance and a wide linear range?from 5 fM to 50 pM?with a detection limit as low as 2.29 fM.This sensing strategy based on multiple signal amplification has guiding significance for the design of photoelectrochemical sensing platform.3.CdTe QDs co-modified with mercaptopropionic acid and cyclodextrin?MPA/SH-?-CD@CdTe QDs?,and cyclodextrin-modified gold nanoparticles??-CD@Au NPs?were successfully prepared.A photoelectrohemical DNA sensor was successfully constructed,which based on the host-guest interaction between ?-cyclodextrin(?3-CD?and adamantane?ADA?and mimetic enzyme catalysis.Through experimental verification,CdTe quantum dots were oxygen-sensitive,and the photocurrent was related to the content of oxygen in the electrolyte.In the presence of target DNA,ADA-tagged hairpin DNA was opened and formed double-stranded DNA structure that separated the ADA at both ends,thereby was coupled to the electrode surface through host-guest recognition.Subsequently,the ?-CD@Au NPs mimetic enzyme was also immobilized to the other end of the DNA duplex through the interaction of host-guest recognition,thereby efficiently catalyzing the oxidation of glucose,consuming the oxygen in the electrolyte,and significantly reducing the photocurrent.Under optimized conditions,the biosensor has good sensing performance,a wide linear range?from 10 fM to 100 pM?,a detection limit of 3.1 fM,high selectivity and stability,and showing great prospect in bioanalysis and DNA detection.