Label-free Photoelectrochemical Biosensors Based On Poly(5-formylindole) Nanocomposites

Photoelectrochemical（PEC）biosensing technology as a new type of analytical method is developed by combining photoelectrochemical processes with biorecognition processes.Compared with traditional optical and electrochemical methods,this method has the advantages of simple equipment,low cost,easy miniaturization,and high sensitivity.A good photoelectrochemical active material is one of the important factors of high sensitivity of PEC analysis technology.Therefore,it is important to develop photovoltaic active materials with high photocurrent intensity.Polyindole and its derivatives are a class of functional polymer materials withgoodconductivity,highphotoelectricactivityforconstructing photoelectrochemical sensors.The polyindoles containing the aldehyde group can not only improve the photoelectric activity of the materials,but also help the immobilization of biomolecules.In this thesis,photoelectrochemical sensors were fabricated by using poly（5-formylindole）nanocomposites as photoelectroactive material.The main contents are as follows:1.Photoelectrochemical immunosensor for the carcinoembryonic antigen detection based on electrochemically reduced graphene oxide and poly（5-formylindole）hybridElectrochemically reduced graphene oxide（erGO）/poly（5-formylindole）（P5FIn）nanocomposites were used to construct a label-free and highly sensitive photoelectrochemical immunosensor to detect carcinoembryonic antigen（CEA）.The experimental results showed that P5FIn/erGO nanocomposites had high photoelectric activity and good conductivity,which were conducive to improving the sensitivity of immunosensor.In addition,the nanocomposites had good biocompatibility and stability,which were conducive to improving the stability of the sensor.The antibody（Ab）was covalently bound to the erGO/P5FIn modified electrode by gold nanoparticles（AuNP）as cross-linking.The immunosensor showed a wide linear response to CEA ranging from 0.0005 to 50 ng mL^-1 and a low detection limit of 0.14pg mL^-1.Additionally,the proposed immunosensor had long-term stability,good reproducibility and high specificity.Good recoveries were also shown when this immunosensor was used to detect CEA in human serum.2.Photoelectrochemical aptasensor based on poly（5-formylindole）/Au nanocomposites for the detection of thrombinA label-free and high-sensitive photoelectrochemical aptasensor for detecting thrombin（TB）was constructed based on poly（5-formylindole）/Au（P5FIn/Au）nanocomposites.The P5FIn/Au nanocomposites were prepared by electrochemical polymerization and were used as a photoelectrochemical substrate for immobilization of thrombin aptamer（TBA）.Because P5FIn can fully absorb light source energy to produce more photogenerated electron-hole pair,the nanocomposite material had high photocurrent signal.Au as a kind of high electroactive material can promote electron transfer and effectively inhibit the recombination of photogenerated electron-hole pair,resulting in enhanced photocurrent strength.The aptasensor was used for the quantitative detection of thrombin and showed a wide linear response ranging from0.001 to10 nM,a low detection limit of 0.2 pM,good stability,reproducibility and selectivity.The aptasensor also showed good recovery and accuracy in the analysis of the actual samples,which indicated that the sensor had good application prospect in the field of biological analysis.3.Photoelectrochemical aptasensor based on electrochemically reduced graphene oxide/poly（5-formylindole）/Au nanocomposites for the detection of aflatoxin B1Based on the electrochemically reduced graphene oxide/poly（5-formylindole）/Au nanocomposites（erGO/P5FIn/Au）,a photoelectrochemical aptasensor was constructed for the high sensitivity detection of aflatoxin B1（AFB1）.Photoelectrochemical tests showed that the charge transfer efficiency,photoelectric conversion efficiency and photocurrent intensity of the material were highly improved after Au and erGO were introduced into the nanocomposite materials.In addition,erGO had a larger specific surface area and good biocompatibility,which was beneficial to increase the load of the aptamer DNA strand.In the absence of the target analyte AFB1,the sensor showed a weak photocurrent signal due to the steric hindrance of the DNA strand.When AFB1existed,the specific binding of target analyte and the aptamer strand led to the stripping of DNA strand from the electrode surface,thus enhancing the photoelectric current signal of the sensor.Under optimal conditions,the photoelectrochemical aptasensor showed a wide linear response ranging from 0.01 to 100 ng m L^-1 and a low detection limit of 0.002 ng m L^-1.The sensor also showed good selectivity and accuracy in the detection of AFB1 in food,which indicated that the sensor had potential application value in food safety detection.