Organic Electrochemical Transistor For H~+ And Na~+ Detection

In recent decades,the application of ion detection in agricultural production,environmental protection,health monitoring and other fields has become more and more common,and ion selective electrodes are the most common and widely used tools for ion detection.The disadvantages such as the need for reference electrode and low detection sensitivity limit its further development.Organic electrochemical transistors（Organic Electrochemical Transistor,OECTs）based on poly（3,4-ethylenedioxythiophene）/polystyrene sulfonate（PEDOT:PSS）have many advantages such as high transconductance,good mechanical flexibility and biocompatibility,and have been widely used in the field of biosensing.In this thesis,H⁺sensitive OECT with super-Nernst limit is constructed by modifying OECT gate with H⁺sensitive polymer,poly（3,4-ethylenedioxythiophene）/bromothymol blue（PEDOT:BTB）,and further explored the method to improve the detection sensitivity of H⁺.At the same time,a highly sensitive Na⁺sensitive OECT was constructed based on spin-coated PEDOT:PSS and Na⁺selective membrane,and the application of OECT in the fields of ion detection was explored.Specifically,this thesis mainly carries out the following aspects of work:（1）Construction and testing of H⁺sensitive OECT:PEDOT:PSS was prepared by alternating current deposition between the source and drain electrodes with a distance of 10μm,and the PEDOT:BTB was modified by linear cyclic voltammetry（Cyclic Voltammetry,CV）on the gate of the microelectrode chip to construct H⁺sensitive OECT.The study found that the H⁺detection sensitivity of the PEDOT:BTB tested by electrochemical method was about 40.03 m V·dec^-1.When the PEDOT:BTB was modified on the gate of the OECT device,it could be observed that the source-drain current(I_DS)of H⁺sensitive OECT gradually increased with the decrease of p H value,and its detection sensitivity to H⁺was about 86.06 m V·dec^-1,which is about1.45 times the Nernst limit(59.16 m V·dec^-1).72 h H⁺response test shows that the device can maintain the sensitivity to H⁺for a long time.（2）Methods to improve the sensitivity of H⁺detection:This thesis studies the influence of the CV times of PEDOT:BTB,the setting of gate voltage（V_G）and the transconductance value of OECT device on the sensitivity of H⁺detection.In the experiment,through electrochemical testing（including open circuit potential and electrochemical impedance spectroscopy）,OECT characteristics testing（including transfer,output,single stage constant voltage test）,the three influencing factors were analyzed in depth respectively.It was found that the PEDOT:BTB with more CV times,the selection of the corresponding V_G at the transconductance intersection,and the higher transconductance value of the OECT device all contributed to the improvement of the H⁺detection sensitivity.Finally,OECT device with H⁺detection sensitivity of 101.49 mV·dec^-1 was prepared by optimizing experimental conditions.（3）Construction and testing of Na⁺sensitive OECT:In order to explore more applications of OECT in the field of ion sensing,Na⁺sensitive OECT was also prepared based on Na⁺selective membrane.The PEDOT:PSS of the device was prepared by spin-coating method,and its conductivity and stability were improved by sulfuric acid treatment.The sensitivity of Na⁺sensitive OECT prepared by the above method can reach 0.79 m A·dec^-1 in the range of 10^-4～10^-1 M Na Cl concentration.At the same time,the response of Na⁺sensitive OECT to Na⁺,K⁺,Ca²⁺was measured by the single stage constant voltage method.It was found that the fluctuation of source-drain current of the OECT for KCl and Ca Cl₂ is very small,which proves that the OECT has a specific selectivity for Na⁺.The results of reversibility test show that the Na⁺sensitive OECT device has good repeatability.