Research And Applications Of Photoelectrochemical Biosensors Based On Polyindole Nanocomposites

Photoelectrochemical（PEC）biosensing combining photoexcitation and electrochemical detection is a new analysis method.Due to the effective separation of photoexcitation and detection,photoelectrochemical sensor has the advantages of low background signals,high sensitivity,easy operation,and fast analysis speed.As the most important component of photoelectrochemical sensors,photoactive materials are directly related to the sensitivity of PEC sensors.Polyindole is p-type organic conductive polymer material with good photoelectric activity.Polyindole has a stable photocurrent signal under visible light.In addition,polyindole has the advantages of good stability,electrochemical activity,easy modification,and large specific surface area.Thus,it has a good application prospect in the field of PEC sensors.Functional groups also have effects on the photoelectric activity and stability of polyindole.In this thesis,polyindole-based nanocomposites with good photoelectric activity are prepared and applied to the construction of high-sensitivity photoelectrochemical sensors.The main contents are as follows:1.Photoelectrochemical aptasensor for aflatoxin B1 detection based on organic-inorganic poly（5-formylindole）/nickel oxide heterojunctionA cathode photoelectrochemical aptasensor for detecting aflatoxin B1（AFB1）is constructed based on poly（5-formylindole）/nickel oxide（P5FIn/NiO）heterojunction.Due to the synergistic effect between organic and inorganic materials,the P5FIn/NiO heterojunction prepared by hydrothermal synthesis and electrochemical polymerization has good photoelectric activity.The stepwise energy level distribution of P5FIn and NiO is beneficial to the rapid transfer of photogenerated electrons and improves the electron-hole separation rate.The P5FIn/NiO heterojunction with large specific surface area and good biocompatibility provides a good platform for the fixation of biomolecules.The amino-modified AFB1 aptamer chain is modified on the electrode surface by forming an imino bond with the aldehyde group of P5FIn.The linear range of the aptamer sensor for AFB1 is 0.005-50 ng mL^-1,and the detection limit is 1.5 pg mL^-1.In addition,the aptasensor has good stability,selectivity and reproducibility,and also has excellent performance in actual sample detection.This sensor has potential value in food safety testing.2.Separated photoelectrochemical aptasensor for thrombin detection based on poly（5-formylindole）/poly（3,4-ethylenedioxythiophene）compositesThe photoactive materials and recognized biomolecules are placed on the same electrode in traditional photoelectrochemical sensor.In this mode,the detection process may damage the photoactive material,resulting in false negative test results.In this section,the ITO electrode modified by poly（5-formylindole）/poly（3,4-ethylenedioxythiophene）（P5FIn/PEDOT）composites prepared by two-step electrochemical deposition is used as the photoelectrode.The ITO modified by erGO is used as the detection electrode and a separated photoelectrochemical aptasensor for detecting thrombin（TB）was prepared.It is determined through energy level calculation that P5FIn and PEDOT have a stepwise energy level distribution.Under visible light excitation,the P5FIn/PEDOT composites has stronger photoelectric activity than pure P5FIn.Er GO has good electrical conductivity,biocompatibility,and a large fold-like morphology.TB aptamer chain is fixed on the surface of the erGO by π-πstacking.After the detection electrode is incubated with TB,the aptamer chain will fall off the graphene surface.The specific detection of TB is achieved through the enhancement of photoelectric signals.This separated photoelectrochemical aptasensor has a wide detection limit of 0.0001-10 nM and a low detection limit of 0.041 p M.The experimental results show that the separated photoelectrochemical sensor has good stability,reproducibility,selectivity and analytical performance.These results also indicate that the sensor has potential application value in the clinical diagnosis of early cancer.3.Ratiometric photoelectrochemical immunosensor for prostate antigen detection based on p-n type poly（indole-5-carboxylic acid）/tungsten trioxide heterojunctionThe p-πconjugate effect in the carboxyl group can strengthen the electron delocalization of polyindole.Thus,poly（indole-5-carboxylic acid）（P5ICA）has good photoelectric activity.However,the poor stability of P5ICA limits its application in the field of photoelectrochemistry.The single-signal detection mode of the photoelectrochemical sensor may have the disadvantages of fluctuations in the photocurrent signal caused by the instrument or the environment.The strategy of combining the ratio detection mode and photoelectrochemical analysis can effectively reduce the background signal interference caused by environmental.In this section,p-n-type poly（indole-5-carboxylic acid）/tungsten trioxide（P5ICA/WO₃）heterojunction was prepared.The N-W bond between P5ICA and WO₃ can enhance the stability of P5ICA.The energy level matching between P5ICA and WO₃ also increases the utilization of visible light and effectively reduces the electron-hole recombination in the heterojunction.Based on the P5ICA/WO₃ heterojunction,a ratiometric photoelectrochemical sensor is prepared for PSA detection.The ratio mode reduces the background signal of the sensor and improves the sensitivity.The sensor has a detection range of 0.0005-50 ng mL^-1 and a low detection limit of 0.12 pg mL^-1.In addition,the ratiometric photoelectric sensor has good accuracy and selectivity for PSA detection,and has good recovery and accuracy in actual sample analysis,indicating that the ratiometric sensor has potential value in the field of biological analysis.