Reversible pH-induced fluorescence colour change of gold nanoclusters based on pH-regulated surface interactions.

To prepare water-dispersible, biocompatible, ratiometric pH nanosensors is challenging. We report here for the first time that the emission colour of NAD+-capped AuNCs responds to the mono-/bidentate anchoring of the phosphoric groups of the ligand. The AuNCs exhibit a high luminescence (21% quantum yield) and an outstanding performance as fluorescent ratiometric pH sensors over a broad pH range.