A smartphone-assisted ratiometric fluorescence sensor based on dual-emission copper nanoclusters for visual detection lead ion

Quantification of fluorescent assays with smartphones has great promise in environmental monitoring for providing on-site visual detection. However, the analytical performance of these fluorescence sensors based on single-color channels is usually unable to satisfy the detection accuracy. Here, we propose a smartphone-assisted ratiometric fluorescence-sensing platform based on dual-emission copper nanoclusters (Cu NCs) for precisely determining Pb2+ concentrations. The Cu NCs were prepared by using dithiothreitol (DTT) as reducing and stabilizing agents, which possess two intrinsic emission centers located at 450 nm and 620 nm, respectively. In presence of Pb2+, the red fluorescence at 620 nm of the Cu NCs were quenched via photoinduced electron transfer process, meanwhile the blue fluorescence at 450 nm could be maintained unchanged. Thus, a ratiometric fluorescence sensing of Pb2+ was facilely fabricated based on the Cu NCs without introducing other fluorescent materials as the reference, allowing sensitive and selective determination of Pb2+ with a limit of detection (LOD) of 2 nM. Moreover, extracting the fluorescence color changes of this sensor under the supporting of a smartphone app, a portable sensing platform was constructed for visual detecting Pb2+ with LOD of 0.05 mu M, showing great potential for on-site monitoring of Pb2+.