High quantum yield copper nanoclusters integrated with nitrogen-doped carbon dots for off-on ratiometric fluorescence sensing of S2- and Zn2.

Pursuing nanomaterials with high fluorescence quantum yields is of great significance in the fields of bioimaging, medical diagnosis, and food safety monitoring. This work reports on orange-emitting aggregation-induced emission (AIE) copper nanoclusters (Cu NCs) integrated with blue-emitting nitrogen-doped carbon dots (N-CDs), which enables highly sensitive detection of S^2- and Zn²⁺ ions through an off-on ratiometric fluorescence method. The highly emissive Cu NCs was doped by Ce³⁺ with a high quantum yield of 51.30 % in aqueous solution. The S^2- can induce fluorescence quenching of AIE Cu NCs/N-CDs from orange to blue, while Zn²⁺ can restore the orange fluorescence. The probe provided linear detection ranges of 0.5-170 μM for S^2- and 0.05-200 μM for Zn²⁺, with detection limits of 0.17 μM and 0.02 μM, respectively. Moreover, a smartphone assistant ratiometric fluorescent test strips were developed for the rapid and visual detection of S^2- and Zn²⁺. The AIE Cu NCs/N-CDs probe exhibited diverse fluorescence color responses, high fluorescence stability, and low cytotoxicity. The ratiometric system was successfully applied to the detection of S^2- and Zn²⁺ in real water samples as well as in cellular and living imaging, demonstrating its potential in biochemical analysis and food safety monitoring.