A convenient purification method for metal nanoclusters based on pH-induced aggregation and cyclic regeneration and its applications in fluorescent pH sensors

Herein, we report a convenient approach to purify water-soluble bovine serum albumin (BSA)-capped metal nanoclusters by pH-induced precipitation under acidic conditions. The fluorescence of metal nanoclusters could be completely recovered upon the re-dispersion of nanoparticles into basic media. BSA metal nanoclusters have been prepared to monitor pH at highly acidic medium. When pH decreased, the fluorescence of the nanoclusters under a UV lamp decreased and completely disappeared after pH 4. And a fluorescent pH sensor for pH monitoring has been developed based on the “OFF–ON” signal switch of the gold clusters agarose hydrogel.