Multifunctional Fluorescent Copper Nanoclusters for Ag⁺ Sensing, Anticounterfeiting, and Blue/White Light-Emitting Diodes

Copper nanoclusters (CuNCs) with bright blue-emitting fluorescence have been synthesized via a simple one-pot process using 2-mercapto-1-methylimidazole (MMI) as a stabilizer. The as-prepared MMI-CuNCs exhibited a high quantum yield of 19.2%, a long luminescence lifetime of 10.57 μs, and excellent photostability. Significantly, the fluorescence intensities of MMI-CuNCs were effectively quenched with addition of Ag⁺ ions, and the MMI-stabilized CuNCs were developed as a sensitive fluorescent nanoprobe for the label-free determination of silver ions for the first time. The fluorescence sensor provided a fast linear response toward Ag⁺ in the range of 0.025–50 μM, with a detection limit of 6.7 nM. The fluorescence quenching mechanism was ascribed to an agglomeration-induced effect and static quenching. A fluorescence sensing platform was successfully applied for Ag⁺ detection in human serum samples with good accuracy and high reproducibility, signifying the practical applicability of the assay. Additionally, MMI-CuNCs displayed good solid-state blue emission and are suitable for security ink applications. The MMI-CuNCs were utilized as a color conversion layer to construct blue- and white-light-emitting diodes (LEDs) with excellent white light properties by a facile combination of MMI-CuNCs and UV LED chips. This result facilitates multiple functions of MMI-CuNCs in the application of label-free sensors, anticounterfeiting, and optical devices.