Protein-directed synthesis of pH-responsive red fluorescent copper nanoclusters and their applications in cellular imaging and catalysis

The development of functional copper nanoclusters (Cu NCs) is becoming increasingly widespread in consumer technologies due to their applications in cellular imaging and catalysis. Herein, we report a simple protein-directed synthesis of stable, water-soluble and fluorescent Cu NCs, using BSA as the stabilising agent. Meanwhile, in this study, hydrazine hydrate (N₂H₄·2H₂O) was used as the reducing agent. N₂H₄·2H₂O was a mild reducing agent suggesting that all processes could be operated at room temperature. The as-prepared Cu NCs showed red fluorescence with a peaking center at 620 nm (quantum yield 4.1%). The fluorescence of the as-prepared BSA-Cu NCs was responsive to pH in that the intensity of fluorescence increased rapidly by decreasing the pH from 12 to 6. Besides, with an arresting set of features including water-dispersibility, red fluorescence, good biocompatibility, surface-bioactivity and small size, the resultant BSA-Cu NCs could be used as probes for cellular imaging and catalysis. In this study, CAL-27 cells and the reaction of oxidation of styrene are used as models to achieve fluorescence imaging and elucidate the catalytic activity of the as-prepared BSA-Cu NCs.