Tunability of Morphology and Conductivity of PPy Films Deposited Au/PI Flexible Electrode for High‐Sensitivity EGFET‐Based pH Sensor

Abstract This work presents EGFET‐based pH sensors utilizing polypyrrole (PPy) films on flexible Au/PI substrates as sensing electrodes. The PPy films are synthesized on the Au electrodes via vapor‐phase polymerization using FeCl 3 solutions at concentrations of 0.1, 0.4, 0.8, and 1.2 m , as the oxidant. Characterization of SEM, FTIR, Raman scattering, and UV–vis reveals that the morphology, doping, and bandgap ( E g ) of the synthesized PPy films strongly depend on FeCl 3 concentration. The fabricated PPy‐Au sensing electrodes are integrated into an EGFET configuration and evaluated in buffers with pH values of 2.5, 4.3, 6.5, 7.5, and 9.2. The sensors exhibit excellent sensitivity, increasing from 58.19 µA/pH for PPy‐0.1 to 71.51 µA/pH for PPy‐1.2 as FeCl 3 concentration increases. Response times lengthen with higher FeCl 3 concentrations, while hysteresis and drift decrease. Stability assessments of the PPy‐0.8 and PPy‐1.2 sensors over a temperature range of 25–45 °C and 70 h show standard deviations of 6.85 µA and 3.88 µA, respectively, indicating robust long‐term performance. High selectivity is confirmed by testing the PPy‐1.2 sensor under pH shifts from 4.3 to 6.5 in the presence of interfering ions (e.g., Na⁺, Ca 2 ⁺, lactic acid).