Can the pH at the air/water interface be different from the pH of bulk water? [Physical Sciences]

A recent article in PNAS (1) reports stable pH gradients in aqueous phosphate buffer microdroplets based on the pH dependence of surface-enhanced Raman spectroscopy (SERS) signals from 4-mercaptobenzoic acid–functionalized gold nanoparticle pH probes. The probing SERS signals were a 1,470-cm−1 shift assigned to a COO− stretching and a 1,710-cm−1 shift...

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