Flexible Polypyrrole-Based pH Sensors via Oxidative Chemical Vapor Deposition.

Abstract

The dynamic physicochemical environment of healing wounds provides valuable diagnostic information, with pH serving as a key biomarker for infection, inflammation, and tissue regeneration. However, the development of flexible, biocompatible, and stable pH sensors that can be seamlessly integrated into wearable platforms remains challenging. Here, we report a strategy to fabricate electrically conductive, pH-responsive bioelectronic sensors based on ultrathin polypyrrole (PPy) films deposited via oxidative chemical vapor deposition (oCVD). The resulting flexible sensors enable monitoring of physiologically relevant pH changes (4-9) and exhibit modulation of electrical conductivity up to two orders of magnitude, reaching 304 S.cm^-1 (pH 4). Grazing-incidence wide-angle X-ray scattering reveals enhanced structural order and efficient π-π stacking with increasing dopant concentration, leading to improved charge transport. Complementary spectroscopic analyses demonstrate that reversible protonation-deprotonation of the PPy backbone, governed by dopant counterion exchange, underlies the pH-dependent electrical response. The all-polymer pH sensors display high sensitivity, stability, and repeatability. Moreover, the substrate-independent nature of oCVD enables the fabrication of pH-sensing patches and spatially patterned micro-islands, facilitating seamless integration into smart wound dressings for spatiotemporally resolved bioelectronic monitoring. This work advances the design of flexible, wearable pH sensors and provides opportunities for real-time wound-healing monitoring.