Noninvasive Monitoring of Skin pH Changes Induced by Microneedle Electroporation

The pH of the skin surface plays a critical role in maintaining epidermal homeostasis and barrier function. Microneedle electroporation represents a pivotal advancement in transdermal drug and gene delivery; however, the concomitant electrochemical reactions that pose risks of cutaneous pH perturbation have not been experimentally characterized. This study establishes a quantitative, noninvasive analytical methodology to visualize and measure these microenvironmental changes in situ. A high-resolution ratiometric fluorescence imaging approach was employed using the pH-sensitive probe 8-hydroxy-1,3,6-pyrene trisulfonic acid in combination with confocal microscopy. The native pH gradient in ex vivo mouse skin was mapped, confirming an acidic stratum corneum (pH 6.4 ± 0.2) transitioning to a near-neutral dermis (pH 7.1 ± 0.2). Direct-current (DC) electroporation with microneedle electrodes resulted in significant and spatially localized acidification near the anode. After a 150 V, 100 ms pulse, the maximum pH deviation reached 1.11 units (pH 6.1 ± 0.1, p < 0.001), indicating substantial perturbation of cutaneous pH balance. In contrast, application of a bipolar alternating current (AC) sine-wave pulse prevented these pH changes, preserving the physiological pH gradient throughout the treated area. These results demonstrate that AC electroporation can reduce electrochemical side effects, such as pH disruption. This study provides direct, quantitative visualization of microneedle electroporation-induced pH disturbances in skin and identifies AC waveform modulation as a promising strategy to mitigate pH alterations associated with dermal electroporation protocols.