Fabrication And Characterization Of Molecular Imprinting-Organic Electrochemical Transistor Sensors

Organic electrochemical transistors(OECTs)have the potential to be used in biosensors due to their many advantages like small size,low cost,easy fabrication,good biocompatibility and low operating voltage.However,its selectivity is not satisfactory,which restricts its application in the sensor.Molecularly imprinted polymers(MIPs)are polymers that have an ability to specifically recognize specific molecular,which have been widely used in sensors due to the advantages of easy fabrication,good stability and high selectivity.Therefore,the integration of MIP in OECTs is a reasonably effective way to improve the selectivity of OECTs in biosensors.However,MIP-modified OECTs have not yet been explored or published.In this thesis,we focused on the selectivity of OECT sensors.First,high sensitivity and high selectivity OECT sensor modified with MIP(MIP-OECT)was prepared using readily oxidizable ascorbic acid(AA)as a template and o-phenylenediamine(o-PD)as a functional monomer.Next,the chiral detection effect of this method on chiral substances(histidine)was studied,and good results were obtained.Furthermore,the applicability and sensing mechanism of this type of MIP-OECT sensors in chiral detection were studied in depth by using aromatic chiral amino acids(tryptophan and tyrosine)as template molecules,and the practical application of MIP-OECT sensors were also studied.The main study results of this thesis are as follows:1.Preparation and Properties of Ascorbic Acid MIP-OECT Sensor with High Sensitivity and High SelectivityMIP-OECT sensor was prepared by using AA as templates and o-PD as functional monomer.Cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS)measurements were carried out to monitor the stepwise fabrication of the modified electrodes and the adsorption capacity of the modified electrodes.Atomic force microscopy(AFM)was employed for examining the surface morphology of the electrodes.Important detection parameters,pH and detection temperature were optimized.The MIP-OECT sensor exhibited a low detection limit of 10 nM(S/N>3)and a sensitivity of 75.3 ?A channel current change per decade under optimal conditions.Furthmore,the MIP-OECT sensor exhibited excellent specific recognition ability to AA,which prevented the interference from other structurally similar compounds and common metal ions.In addition,a series of vitamin C beverages were analyzed to demonstrate the feasibility of the MIP-OECT sensor.2.Selective recognition of the histidine chiral enantiomer MIP-OECT sensorChiral recognition of a-amino acids is attracting increasing interest due to the importance of ?-amino acids in protein metabolism as well as in food products and pharmaceuticals.The histidine enantiomer recognition sensors were prepared by electro-polymerization using acrylamide as functional monomer and D/L-His as templates.Infrared spectroscopy and scanning electron microscopy showed that MIPs were successfully prepared.The changes in channel current were proportional to D-His and L-His concentrations from 100 nM to 10 ?M,with sensitivities of 8.2 and 22.7 ?A decade-1,and the detection limits of 10 nM and 100 nM(S/N>3),respectively,under the optimal conditions.Furthermore,the highly selective MIP film allowed to differentiate L-His from D-His or D-His from L-His.In terms of selectivity,the tests suggested apparent differences in channel current changes between L-His and interferences including common metal ions.In addition,the L-His MIP-OECT sensor can be used for the detection of L-His in human urine.3.Study on the MIP-OECT sensors and detection mechanism of the chiral enantiomers of weakly oxidative aromatic amino acidsIn order to study the applicability and sensing mechanism of this type of MIP-OECT sensors in chiral detection,the MIP-OECT chrial sensors were prepared with D/L-Trp and D/L-Tyr as templates.CV,EIS and AFM were used to analyze the electrical properties and morphologies of different modified electrodes,which proved that the modified electrodes were able to selectively recognize the templates.The sensor showed sensitivity of 3.19 and 3.64 ?A ?M-1 for L-Trp and L-Tyr with the detection limit of 2 nM and 30 nM(S/N>3).The selectivity factors proved that the sensors can be used for the chiral recognition of Trp and Tyr.The detection mechanism is:MIP film selectively adsorpted the templates,and then electrocatalytic oxidation of them to produce Faraday current,resulting in an increased in effective gate voltage,and ultimately leading to a decrease in channel current.In addition,MIP-OECT sensors prepared with L-Trp and L-Tyr as templates can be used for the detection of L-Trp and L-Tyr in amino acid tablets.