Photoelectrochemical Aptasensing Of Aflatoxin B1 And Adenosine Triphosphate Based On Inorganic Semiconductor Composite Materials

Aflatoxin B1（AFB1）existing widely in natural foods,is recognized as one of the most carcinogenic substances.Adenosine phosphate（ATP）is a very important energy substance in organism,which plays a key role in various physiological metabolic activities.Abnormal ATP levels can lead to a variety of diseases.Therefore,it is of great significance to develop efficient methods for rapid and sensitive detection of AFB1 and ATP.Photoelectrochemical analysis as a newly developed method based on photoelectric conversion has a low background signal and high sensitivity.The development of high-performance photoactive materials is the key to improve the sensitivities of PEC biosensors.Aptamer as a specific molecular recognition tool has been widely used for biosensing,due to their advantages of facile synthesis,low cost,good thermal stability,and and easy labeling.In this thesis,two kinds of high-performance photoelectric active materials were developed,and PEC detection of AFB1 and ATP was realized based on target-induced aptamer structure switch.The main contents are as follows:（1）Cobalt-doped tungsten trioxide（Co-WO₃）nanorods/gold nanoparticles（Au NPs）were used for PEC sensing of AFB1 based on aptamer structure switch and horseradish peroxidase（HRP）-induced biocatalytic precipitation.Because of the decreased band gap and the increased visible light absorption of Co-WO₃ nanorods,Co-WO₃ nanorods show higher PEC activity than WO₃ nanorods under the visible light irradiation.Co-WO₃ nanorods decorated with Au NPs offer superior PEC activity to Co-WO₃ nanorods due to the surface plasmon resonance effect.To construct a PEC aptasensor,short DNA strands（DNA₁）are immobilized on the Co-WO₃-Au NPs modified indium-tin oxide electrode.HRP-labeled aptamer hybridizes with the DNA₁ on the photoelectrode in the absence of AFB1,and precipitations generated by HRP catalysis can quench the photocurrent of the photoelectrode.In the presence of AFB1,HRP-labeled aptamer does not hybridize with the DNA₁ due to the formation of aptamer-AFB1 complex,and thus high photocurrent signal is achieved.The PEC aptasensor for AFB1 detection shows a broad linear range from 5 fg m L^-1 to 10 ng m L^-1,with a detection limit of 1 fg m L^-1.（2）Cd Se quantum dots（QDs）-decorated Zn In₂S₄ nanosheets were used for PEC sensing of ATP based on aptamer structure switch and exciton-plasmon interactions.The formation of Cd Se/Zn In₂S₄ promotes the separation of photogenerated electron and hole,and enhances the absorption of visible light.Therefore,Cd Se/Zn In₂S₄,as a new photoelectric material,can exhibit better PEC activity than Zn In₂S₄nanosheets and Cd Se QDs under visible light irradiation.To construct a PEC sensor,Au NP-labeled strand DNA（c-DNA）was immobilized on the Cd Se/Zn In₂S₄ photoelectrode and hybridized with an aptamer（Apt）to form a double-stranded DNA.In this case,Au NPs are kept away from Cd Se/Zn In₂S₄,so the exciton-plasmon interaction between Cd Se QDs and Au NPs can greatly quench the photocurrent of the photoelectrod（"signal off"state）.In the presence of target ATP,the Apt dissociates from the double-stranded DNA due to the formation of Apt-ATP complex,and the c-DNA with complementary bases at both its ends forms a hairpin structure in the presence of Mg²⁺.As a result,Au NPs labled on the c-DNA will be in close contact with Zn In₂S₄/Cd Se,so enhanced photocurrent can be obtained（"signal on"state）due to the great plasmon–exciton coupling effect.The PEC aptasensor for ATP detection shows a broad linear range from 0.2 p M to 1μM,with a detection limit of0.1 p M.