Mechanistic insights into redox-protonation coupled fluorescence switching in peptide-mediated gold nanoclusters for precision tumor imaging and resection.

Photoconvertible fluorescence probes are indispensable tools for rapid and accurate tissue diagnosis. Herein, we developed peptide-coated gold nanoclusters (AuNCs) capable of fully reversible red/green fluorescence switching. Mechanistic studies revealed that the photoconversion behavior of AuNCs is dictated by the interdependent effects of Au valencies, tyrosine phenol forms, and the interactions between Lys/Arg amino groups and the gold cores. This fluorescence switching involves two key processes: (1) a gradual red-to-green shift regulated by a slow reduction reaction that modulates the Au(I)/Au(0) ratio and phenol oxidative states; (2) an instantaneous green-to-red transition triggered by mildly acidic pH, which promotes protonation of phenol and amino groups, thereby disrupting their interactions with the gold cores. Due to their high pH sensitivity, these AuNCs exhibit distinct and cell-type-specific fluorescence responses, allowing unambiguous discrimination between normal and tumor cells based on intracellular pH differences. In vivo experiments further confirmed the probe's ability to selectively and rapidly delineate tumor tissues, highlighting its potential as a fluorescence-guided navigation tool for minimally invasive cancer surgery.