Organic Electrochemical Transistor Based On Ionic Liquid

In recent years,organic electrochemical transistors(OECT)based on poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate)(PEDOT:PSS)have been widely used for high-sensitivity biosensing.PEDOT:PSS films can be prepared by alternating current(AC)electrodeposition method,and their structure and morphology can be adjusted by electrochemical parameters such as the electrolyte concentration,the amplitude,and frequency of the alternating voltage.Although PSS polymer is beneficial for the solvation of 3,4-ethylenedioxythiophene(EDOT)monomer,its conductivity is poor,and it has the shortcomings of weak acidity and instability in the aqueous solution,which seriously affects the device performance of OECT and its application in the field of biosensing.In this paper,using ionic liquid(IL)as the solvent for the monomer,single-phase PEDOT-based high-stability OECTs are prepared.By constructing an OECT aptamer biosensor(OECT-AB),the potential application of PEDOT OECT in the detection of adenosine triphosphate(ATP)is explored.Specifically,this article mainly carries out the following aspects of work:(1)Preparation of high stability OECTs:Based on the proton-type ionic liquid,n-hexylamine bistrifluoromethanesulfonimide(HHexam(Tf₂N)),PEDOT film is electrodeposited between 5 pairs of microelectrodes with a spacing of 10?m.The influence of AC amplitude and frequency on the morphology of PEDOT film is explored.The study finds that when the AC amplitude is fixed,semiconducting films'width gradually decreases with the increase of the frequency.On the other hand,when keeping the AC frequency constant,increasing the voltage amplitude from 5.0 V to 6.0 V,although the average width does not change significantly,the film's porosity increases.Energy dispersive spectroscopy(EDS)and Raman spectroscopy(Raman)test results show that:based on AC electrodeposition in ionic liquid,the co-electrodeposition of anions[Tf₂N]^-and radical cations[EDOT]ⁿ⁺can be realized.As such,this paper realizes an OECT that can maintain high stability during 150 hours of continuous measurement.Specifically,the maximum transconductance,on/off current ratio,and hysteresis are stable at 2.79 m S,504,and 0.12 V,respectively.The transient behavior is also very stable,with a time constant of 218.6 ms.(2)Gate functionalization of PEDOT OECT:Firstly,nucleic acid aptamers are designed and processed according to the molecular structure of ATP.After that,probe fixation,6-mercaptohexanol(MCH)blocking,and electrochemical verification of ATP sensing are carried out in turn.Experimental results of probe fixation and MCH blocking are verified by cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS).Electrochemical verification of ATP sensings is achieved by square wave voltammetry(SWV).The experimental results show that the sequence of the nucleic acid aptamer designed in this paper is reasonable.When the ATP concentration ranges from 10^-8 M to 10^-4 M,the SWV peak current decreases with the increase of ATP concentration.(3)OECT based ATP sensor verification:This chapter uses commercialized IL,1-butyl-3-methylimidazole hexafluorophosphate(BMIMPF₆)as the solvent to verify the universal applicability of ionic liquids in the preparation of high-stability OECTs.In detail,Ag/Ag Cl electrode was selected as the OECT gate for device performance calibration.Then,electrodes functionalized with aptamers are used as the OECT gate for ATP biosensing verification.It is found that when the maximum transconductance of the Ag/Ag Cl gated OECT is 2.51 m S,the ATP sensing in the concentration range of 10^-12 M to 10^-6 M can be achieved.The steady-state test results show that:with the increase of ATP concentration,the maximum drain current and maximum transconductance increase;the transient test shows that the response time decreases with the increase of ATP concentration,that is,the response speed increases.(4)Performance optimization of PEDOT OECT:Chloroauric acid is mixed into the electrolyte of EDOT monomer solvated by BMIMPF₆ to realize co-electrodepositions.EDS results show that Au nanoparticles and PEDOT films are successfully deposited onto the electrode.The higher the amount of chloroauric acid,the higher the Au nanoparticles'content in the PEDOT film.The device characterization of OECT prepared by different amounts of chloroauric acid showed that as Au nanoparticles'content increases,the maximum transconductance and maximum source-drain current of OECTs increase,which lays the experimental foundation for OECT-based aptamer sensor performance optimization.