Microfluidic Ion Transport In Organic Electrochemical Transistors

Organic electrochemical transistors(OECT)are widely used in the field of biosensing because of their good biocompatibility,low operating voltage and high transconductance.From the birth of OECT to now,although the device physics and model of OECT have been continuously improved,the mechanism of microfluidic ion transport in OECT is not yet clear,so its ion transport is still the key factor affecting the performance of OECT devices.This paper focuses on the microfluidic ion transport in OECT and the OECT-based ATP sensor.(1)The organic semiconductor film of OECT is prepared by cyclic voltammetry.Specifically,the growth of organic semiconductor thin films is controlled by changing the voltage scanning range and scanning rate of the working electrode,the morphology of the thin films is characterized by SEM and super depth-of-field confocal microscope,and the electrical properties of semiconductor thin films are characterized by digital source meter.The experimental results show that when the working electrode voltage range is 2V～-2V and the scanning rate is 500 V/s～650 V/s,the organic semiconductor thin films are uniform and compact,and the electrical properties of the films are good.With the increase of the voltage or the acceleration of the scanning rate,the growth rate of the film is also accelerated,and there will be polymer accumulation in the middle of the film,which will lead to the fracture of the film and the decline of electrical properties.When the voltage is low or the scanning rate is small,the growth of organic semiconductor films is slow,the structure is loose,and the morphology is poor.After extensive testing,the best preparation method of organic semiconductor thin films was obtained.(2)The mechanism of ion transport in OECT is studied.Using the electrode deposited with organic semiconductor film as the working electrode,the transport properties at different working voltages and electrolyte concentrations were studied by cyclic voltammetry and electrochemical impedance spectroscopy(EIS).The results show that the ion transport in OECT is controlled by electrophoresis and diffusion,and the ion transport has a synchronous effect on the carrier transport and transport in the organic semiconductor layer.Furthermore,by testing the transient response of OECT,it is concluded that the higher the gate voltage or the higher the ion concentration,the shorter the response time of the channel current,which indicates that the rate of cation entering the semiconductor channel is faster,but the discharge rate is slower.By adding the gate of OECT,the double liquid gate transistor is fabricated,and the transfer curve of the device under the double gate control is tested.the experimental results show that the combination of the two gates can increase the regulation range of the channel current,and the gate voltage and threshold voltage corresponding to the maximum transconductance can be controlled linearly,and the position of the high-performance region can be adjusted,thus realizing the high precision regulation of ion transport.Finally,the transport in electrolyte and organic semiconductor thin films is simulated by multi-physical field simulation software,Comsol Multiphysics,and the following conclusions are drawn: the larger the gate capacitance is,the higher the gate voltage is,and the higher the transport efficiency is,and there is a positive correlation between ion transport and gate voltage.(3)The ATP biosensor based on OECT is constructed to detect the concentration of ATP.The high current OECT device is fabricated by spin coating method,and its stability is tested to ensure that the device can be effectively applied to the sensing test of ATP.The aptamer was modified on the surface of the gold grid,and the gate was incubated in different concentrations of ATP aqueous solution and the transfer curve was tested.In order to ensure the single variable and the amplification performance of the device without affecting the use of the device,only one gate is used,and the scanning range of the gate voltage is set to-0.3V～+0.9V.In addition,according to the conclusion of ion transport,a modified Imurv theoretical model is constructed.The experimental results verify the effectiveness of the theoretical model,and the linear range of ATP concentration detection of ATP aptamer sensor based on OECT is 10-11mol/L～10-6mol/L,and the detection limit is 10-11mol/L.This is about four orders of magnitude smaller than the detection limit of the traditional electrochemical detection method,and greatly improves the detection range of ATP.