Interfacial origin of label-free potentiodynamic fingerprints during bacterial growth in blood culture

Bloodstream infections require rapid microbiological diagnosis, yet conventional blood culture primarily detects microbial growth without providing direct information on pathogen identity. We previously reported a label-free potentiometric platform integrated into blood culture bottles that generates microorganism-specific electrochemical fingerprints, although the physicochemical origin of these signals remained unclear. Here, we investigated whether these fingerprints arise from bulk metabolic changes or from bacteria-electrode interfacial processes. A compartmentalized blood culture system physically separating Escherichia coli from the sensing electrodes showed that diffusible metabolites and bulk acidification alone did not reproduce the potentiometric signature observed in the presence of bacterial cells. Time-resolved electrochemical impedance spectroscopy performed at the evolving open-circuit potential further revealed marked interfacial changes coincident with potentiometric detection. At 0.1 Hz, bacterial growth produced decreases in impedance modulus of approximately 125 kΩ and 8 kΩ on polyaniline and iridium oxide electrodes, respectively, together with material-dependent phase changes. These observations indicate that the electrochemical fingerprints primarily reflect dynamic bacteria-electrode interactions rather than bulk pH variations alone. The results support a model involving bacterial adhesion, local metabolic activity and early biofilm-associated interfacial reorganization, and provide a mechanistic basis for label-free electrochemical monitoring of bloodstream infections.