Localized pH modulation by palladium electrochemistry for reagent-free regeneration of biosensing systems

Localized electrochemical control of pH could enable reagent-free regeneration, conditioning, and actuation of biosensing systems, but practical design rules for integrating solid-state pH modulators with biointerfaces remain poorly defined. Here, we systematically characterized electrochemical pH modulation by palladium electrodes in an integrated microfluidic platform, examining how electrode morphology, applied potential, buffering capacity, and diffusion restrictions govern the rate, magnitude, and spatial propagation of pH changes. In 0.1× PBS, local pH was modulated from 7.4 to 4.6 under anodic bias and 11.6 under cathodic bias within 20–30 min (at a distance of 1 mm from the palladium electrode), while in 1× PBS the same biases produced attenuated but still substantial shifts from 7.4 to 4.6 and 10.8 over 60 min. Increasing the Pd electrode’s electrochemical surface area primarily accelerated pH modulation, while buffer strength and restricted transport suppressed both its magnitude and spatial propagation. We then evaluated the ability of palladium-driven pH modulation to perturb the response of electrochemical aptamer biosensors and regenerate peptide-mediated affinity capture. Cathodic operation, i.e., alkalinization, qualitatively reproduced the expected pH-dependent behavior of methylene blue-labeled aptamer electrodes, but anodic operation, i.e., acidification, caused rapid signal degradation, including elevated background current and loss of a resolvable redox peak over time. In contrast, palladium-driven acidification proved sufficient to trigger release of IgG2 from immobilized peptide receptors over three binding-regeneration cycles. These results establish palladium electrochemical pH modulation as a practical strategy for localized control of pH-sensitive biorecognition, while identifying important constraints for operation near redox-active electrochemical biosensors.