Tracing Protons within Electrochemically Active Biofilms via Real-Time pH Mapping
Yuyi Gu, Xiang Qi, Pengfei Huo, Ziwei Kou, Yijun Yin, Wentao Wang, Xia Huang, Peng Liang
Abstract
Accurately characterizing the proton’s spatiotemporal distribution is critical for elucidating proton/electron generation and transfer mechanisms in electroactive biofilms (EABs). This study employed ratiometric fluorescence sensing for nondestructive, real-time pH mapping in current-producing EABs. The distribution of protons in EABs is determined by both their generation, which is electron donor-dependent, and their transfer, mediated by concentration gradients and buffering effects. Real-time pH mapping evidenced that under low organic conditions (≤0.4 g/L NaAc) in a PBS-free system, proton diffusion driven solely by concentration gradients prevented internal acidification (pH ≥ 6). However, elevated organics (0.8 g/L NaAc) triggered excessive proton accumulation exceeding transfer capacity, resulting in pronounced acidification (pH < 6) and subsequent electroactivity suppression. It also showed that while employing PBS maintained a neutral pH (∼7) for sustained current generation, it concurrently diminished the intrinsic proton concentration gradient, impairing proton diffusion efficiency. Finally, the electron flux was further derived in two ways: converted from the stoichiometric relationship with proton flux ( J e, cal ) and calculated from the measured current ( J e, test ) by applying proton flux, and a better linear fitting correlation was achieved when there was no PBS. This evidences the possibility to trace electron transfer through monitoring protons.