Semi-quantitative and visual assay of copper ions by fluorescent test paper constructed with dual-emission carbon dots.

A novel, simple and effective dual-emissive fluorescent probe for the sensitive and selective detection of Cu(ii) has been developed by mixing blue carbon dots and orange carbon dots, with a sensitive detection limit of 7.31 nM. The blue fluorescence can be selectively quenched by Cu(ii), while the orange fluorescence is a internal reference, resulting in a distinguishable fluorescence color change from blue to orange under a UV lamp. Meanwhile, its as-prepared text paper provides a convenient and simple approach for the visual detection of Cu(ii) and successfully applied in real water samples, with a dose-discerning ability as low as 50 nM. The methodology reported here opens a novel pathway toward the real applications of fluorescent test papers.