Programmable Single-Stranded DNA Layers as Modulators of Nanoscale pH at Electrocatalytic Interfaces

Control of the local reaction environment at electrocatalytic interfaces is crucial for determining the activity and selectivity of many electrochemical reactions. Here, we demonstrate that single-stranded DNA (ssDNA) layers with anionic phosphate backbones can serve as ionomer-like coatings that modulate local pH. On gold nanoparticle (AuNP) electrocatalysts, ssDNA layers enable nanoscale control of the interfacial environment by independently controlling coating thickness through strand-length variation and internal phosphate backbone networking through sequence-encoded base-pairing interactions. We find that ssDNA layers modulate the activity and selectivity of hydroxide ion (OH^-)-involving reactions in a sequence-dependent manner on AuNPs, as exemplified by the hydrogen evolution and glycerol oxidation reactions. Through structure-activity analysis, temperature-dependent experiments, and ssDNA constructs with systematically varied base-pairing, we identify base-pairing interactions within ssDNA layers as the key determinant governing the catalytic behavior. Operando surface-enhanced Raman spectroscopy reveals an ssDNA-mediated regulation mechanism in which the anionic phosphate backbones induce Donnan exclusion of OH^- at the nanoscale interface, with the extent of OH^- buildup or replenishment strongly dependent on base-pairing interactions. Our results suggest ssDNA as a programmable platform for engineering nanoscale reaction environments and propose design principles for ionomer-like architectures in electrocatalysis.