Screen-printed potassium-selective organic electrochemical transistors: Electrical and electrochemical investigation of ion-sensing mechanisms

: Potassium-selective organic electrochemical transistors (OECTs) provide a route for coupling ion recognition with amplified electronic readout in low-voltage sensing platforms. Here, we report a multilayer screen-printed OECT incorporating Ag/AgCl contacts, carbon conductors, a polyethylene glycol (PEG)- and Tween 80-modified PEDOT:PSS channel, dielectric encapsulation, and a potassium ionophore III-based ion-selective membrane. The electrical and electrochemical response of the device was investigated over KCl concentrations from 1.0 × 10 -4 to 1.67 M using output and transfer characteristics, transient gate modulation, cyclic voltammetry, electrochemical impedance spectroscopy, and interference measurements. Increasing K + concentration produced progressively stronger drain-current modulation, yielding a current sensitivity of 2 μA decade -1 (R 2 = 0.9918) and an equivalent gate-voltage-shift sensitivity of 59.8 mV decade -1 (R 2 = 0.9953). Transient measurements showed reversible and concentration-dependent switching, while cyclic voltammetry revealed increasing anodic and cathodic current magnitudes with increasing KCl concentration. Impedance spectroscopy further showed a concentration-dependent reduction in effective electrochemical impedance and enhanced low-frequency capacitive behavior. The device exhibited preferential response to K + over NH 4 + , Na + , Mg 2+ , and Ca 2+ , with drain-current modulation approximately 1.3–4.8 times larger than that of the tested interferents. The combined measurements establish a direct relationship between selective K + transport, interfacial electrochemical processes, and modulation of electronic conduction in the PEDOT:PSS channel, providing mechanistic insight into ion sensing in screen-printed OECTs.