A PEDOT: PSS-based miniature sodium sensor using polarization technique to improve reproducibility

A major obstacle in the development of solid contact ion-selective electrodes (SC-ISEs) is the frequent calibration procedures due to the low reproducibility of standard potential(E⁰) and the unstable signals. To address these challenges, we developed an all-solid state miniature sodium ion-selective electrode (Na⁺-ISE) based on acid-doped poly(3,4-ethylenedioxythiophene)-polystyrene sulphonate (PEDOT: PSS) as the solid contact layer, in combination with an external polarization technique. Acid doping minimized the Coulomb interaction between PEDOT and PSS, inducing significant phase separation and conformational re-aggregation of PEDOT chains, thus creating more contact points to facilitate charge transport and ion-to-electron transduction. The sensor exhibited excellent potentiometric performance with a detection limit of 5.90378 μM and potential drift of 10.99 μV/h. More importantly, external polarization significantly improved E⁰ reproducibility across different electrodes (standard deviation reduced from 57.41 mV to 1.95 mV) and reduced batch-to-batch E⁰ variability. The performance of the potentiometric sensor system was evaluated in inactivated fetal bovine serum, and the measurement results were highly comparable to those of the reference methods with deviation of less than 4 %. The electrochemical sensing system developed in this study provides a novel strategy for highly stable sodium ion sensing, indicating promising potential for calibration-free measurement in medical application.