Ratiometric fluorescent sensing of copper ion based on chromaticity change strategy

Copper ions play a significant role in human bodies, as they are beneficial for many metabolism processes, but excessive Cu2+ may cause various symptoms. Therefore, the development of strategies capable of both sensitive detection and visualization of Cu2+ is greatly important for human health. In this work, a novel ratiometric fluorescence sensor for rapid and visual detection of Cu2+ was designed based on green emission carbon dots (CDs) and red emission CdTe/CdS quantum dots (QDs). We have calculated the chromaticity coordinates of individual CDs and CdTe/CdS QDs, and the chromaticity coordinate of their mixture would change along the line between the two points of CDs and CdTe/CdS QDs in the chromaticity coordinate system. The red fluorescence of QDs can be influenced by Cu2+, and the fluorescence color of CDs-QDs changes from yellow to green as the chromaticity coordinates change with the addition of Cu2+. This traffic-light-type color change was more sensitive to the naked eye compared to conventional single emission-based sensors. This paper not only realized ratiometric fluorescence and visual detection of Cu2+ through a convenient method but also provided a promising strategy of designing an assay kit for trace Cu2+.