Carboxylic Acid‐Functionalized Conjugated Polymer Promoting Diminished Electronic Drift and Amplified Proton Sensitivity of Remote Gates Compared to Nonpolar Surfaces in Aqueous Media

Abstract

AbstractA systematic analysis is used to understand electrical drift occurring in field‐effect transistor (FET) dissolved‐analyte sensors by investigating its dependence on electrode surface‐solution combinations in a remote‐gate (RG) FET configuration. Water at pH 7 and neat acetonitrile, having different dipoles and polarizabilities, are applied to the RG surface of indium tin oxide, SiO2, hexamethyldisilazane‐modified SiO2, polystyrene, poly(styrene‐co‐acrylic acid), poly(3‐hexylthiophene‐2,5‐diyl) (P3HT), and poly [3‐(3‐carboxypropyl)thiophene‐2,5‐diyl] (PT‐COOH). It is discovered that in some cases a slow reorientation of dipoles at the interface induced by gate electric fields causes severe drift and hysteresis because of induced interface potential changes. Conductive and charged P3HT and PT‐COOH increase electrochemical stability by promoting fast surface equilibrations. It is also demonstrated that pH sensitivity of P3HT (17 mV per pH) is an indication of proton doping. PT‐COOH shows further enhanced pH sensitivity (30 mV per pH). This combination of electrochemical stability and pH response in PT‐COOH are proposed as advantageous for polymer‐based biosensors.