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

A 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.