Acetone-triggered self-assembly of L-cysteine-capped copper nanoclusters: a robust "assembly-to-disassembly" strategy...

Copper nanoclusters (CuNCs) are promising fluorophores, yet their practical applications are often limited by low photoluminescence efficiency and poor environmental stability. Herein, we report an acetone-triggered strategy for constructing stable and strongly emissive L-cysteine-capped CuNC submicron assemblies (L-cys-CuNCs/AC) in water. Upon addition of a small amount of acetone, weakly emissive CuNC precursors rapidly evolved into brightly red-emissive assemblies with an emission maximum at 632 nm. Absolute photoluminescence quantum yield measurements revealed a dramatic increase from 0.11% for the precursor dispersion to 19.92% for the assembled state, confirming a substantial assembly-induced enhancement in fluorescence efficiency. Comparative experiments with other water-miscible organic solvents, including methanol, ethanol, acetonitrile, DMF, and DMSO, showed that none of them induced comparable fluorescence enhancement, highlighting the unique role of acetone in triggering the assembly process. The resulting assemblies also exhibited good storage stability in water for over 3 months. Taking advantage of the strong affinity of cyanide (CN^-) toward copper species, we further developed a turn-off fluorescent sensor based on an assembly-to-disassembly process. CN^--induced chemical etching led to structural disintegration of the assemblies and efficient fluorescence quenching, affording a linear response over 10-100 µM with a detection limit of 5.2 µM. The probe was successfully applied to tap water and artificial lake water samples, providing recoveries of 97.6-110.3%. This work provides a simple route for constructing highly emissive CuNC assemblies in aqueous media and demonstrates their potential for cyanide analysis in environmental water samples.