Smartphone-integrated dual-emission fluorescence sensing platform based on carbon dots and aluminum ions-triggered aggregation-induced emission of copper nanoclusters for on-site visual detecting sulfur ions

A ratiometric fluorescence strategy was proposed based on carbon dots (CDs) and self-assembled copper nanoclusters (CuNCs) driven by Al3+ ions for S2- detection. Si-CDs/CuNCs@Al3+ exhibits blue and red emission under single excitation. Interestingly, the red emission of the CuNCs was regularly quenched while the blue fluorescence emission of the CDs was preserved after continuous addition of S2-. The fluorescence spectrometer-based S2- linear range is from 0.5 to 40 μM, with a low detection limit (LOD) of 0.16 μM. The fluorescence response of Si-CDs/CuNCs@Al3+ to S2- exhibits a distinct color change process (red to pink to blue), implying feasibility of visual analysis. A portable fluorescence sensing platform was established using the color-to-value conversion function of a smartphone for accurate visualization and quantitative identification of S2- without spectrometer. The fluorescent test strips prepared with Si-CDs/CuNCs@Al3+ can conduct on-site visual analysis of S2- in the water environment more conveniently and quickly. The linear range of S2- detection based on the smartphone-integrated test strip sensing platform is 1-40 μM, and the LOD is 0.42 μM. This work provides a new horizon for target on-site analysis in environmental samples.