BSA-Capped Dual-Emissive Silver Nanoclusters for Detection of IO₄^– and Cu²⁺ Ions

Dual-emissive protein-capped metal nanoclusters are emerging nanoprobes for ratiometric sensing. Here, we report dual-emissive bovine serum albumin (BSA)-capped silver nanoclusters (AgNCs) with a blue emission band at 450 nm and a far-red emission band at 680 nm. The blue emission is attributed to the BSA capping, while the far-red emission originates from the AgNCs. The intensity ratio of the two bands is susceptible to the presence of IO4– and Cu2+, allowing selective detection of these analytes with a limit of detection (LOD) of 18.8 and 21.6 nM, respectively. These two analytes display different effects on the emission bands. The blue emission band increases with simultaneous diminution of the far-red band in the presence of IO4–; however, only the far-red emission band decreases in the presence of Cu2+ without altering the blue emission. Both the analytes manifested distinct visual changes in the emission color of the AgNCs solution under a UV lamp, which can also be evident from the shift of the Commission Internationale d’Eclairage (CIE) coordinates from (0.48, 0.32) to (0.18, 0.17) and (0.24, 0.25) for IO4– and Cu2+, respectively. IO4– induced a conformational change in BSA, intensifying the blue emission band along with a dynamic quenching of the AgNCs’ emission at 680 nm. In contrast, Cu2+ triggered only a metal exchange method-based quenching of the 680 nm emission with almost no effect on the BSA capping. A smartphone-based on-site detection of IO4– and Cu2+ was also achieved. Inspired by the contrasting fluorescence (Fl) response signals of AgNCs toward IO4– concentration, a simple logic gate circuit was constructed. This investigation will provide important insight into the one-pot synthesis of dual-emissive silver nanoclusters and the ratiometric detection mechanism of IO4– and Cu2+.