Research On The Application Of Photoelectric Conversion Based On Semiconductor Quantum Dots

Photoelectrochemical analysis is a new analytical method based on photochemi-cal,electrochemical and chemical or biological recognition.In view of the PEC sen-sor is an emerging detection technology,it is particularly important to expand the photoelectric conversion unit with superior performance,to develop new detection methods and to construct a new sensing system.In this thesis,the CdS QDs and CdS QDs/TiO₂ composites which be act as photoelectric conversion unit were used to es-tablish a series of sensitive photoelectrochemical detection methods.1.The parameters could influence the efficiency of electrostatic self-assembly were investigated in this paper.A:fter a series of electrode preparation conditions were optimized,the electrodes we fabricated have high photocurrent intensity,which is 8-10 times of the traditional method.Based on CdS QDs multilayers,a sensitive and selective photoelectrochemical?PEC?sensor for thrombin was fabricated by using aptamer?ONS2?-labeled Pt nanoparticles?NPs?as novel energy transfer nanoprobes and thrombin as a 'protective agent'.In the absence of thrombin,ONS2-labeled Pt NPs could be captured on CdS QDs surface by DNA hybridization between the thrombin aptamer?ONS1?and ONS2 and result in photocurrent quenching of sensing system After the specific binding of thrombin aptamer and thrombin,however,the Pt NPs could not be captured on CdS QDs surface.The thrombin aptasensor displayed a linear range from 10-10 mol/L to 10-15 mol/L and a detection limit of 10-16 mol/L.Fab-rication of QDs multilayers with high photoelectric conversion efficiency is of great significance for the future development of PEC biosensor.2.In this paper,a sensitive mercury ion sensor was designed by using CdS QDs/TiO₂ composite as the photoelectric conversion unit.After the coupling of two inorganic semiconductors?CdS QDs and TiO₂?with different band gaps,the perfor-mance of electrode has been greatly improved.After excited by the specific wave-length of light,electronic in CdS QDs will be motivated from the valence band to the conduction band.Then the Excited state electron will move to TiO₂,due to the va-lence band of TiO₂ is lower than CdS QDs.The spatial separation of the e-h pairs in the different semiconductors retards their recombination,and the photoelectric con-version efficiency will be improved.In order to quantitative detect Hg²⁺,we used two complementary single-stranded DNA in this sensor.One strand of DNA?ONS1?with many T bas could form a clip structure with the help of Hg²⁺,which result in ONS2 cannot hybridize with Au NPs marked DNA?ONS2?,and inhibit the de-crease of photocurrent.3.A sensitive photoelectrochemical?PEC?method for Hg²⁺detection is reported,based on the Hg²⁺-mediated structural switch of an oligonucleotide strand and biocat-alytic precipitation?BCP?on a CdS quantum dots electrode.The stable T-Hg-T struc-ture could formed by Hg²⁺ and thymine through coordination This structure could leads to the formation of G-quadruplex and bind hemin to form a stable G-quadrnplex/hemin complex,which could accelerate oxidation of 4-chloro-l-naphthol?4-CN?by H2O₂ to yield the insoluble?BCP reaction?and insu-lating product benzo-4-chlorohexadienone on the photoelectrode,thereby efficiently causing the change in the photocurrent signal This simple PEC sensor could detect aqueous Hg²⁺ at concentrations as low as 4 nM with high selectivity.The recovery rate was 100.8?108.4%,and the relative standard deviation was 5.79%.Therefore,the sensor can be used as an effective tool to detect Hg²⁺.