Ultrafast, sensitive and visual sensing of copper ions by a dual-fluorescent film based on quantum dots

The use of fluorescent sensors is one of the most promising approaches for meeting the growing demand for a sensitive, convenient and cost-effective detection method of metal ions. However, visual sensing based on fluorescent materials remains a challenge due to the hard-to-see changes in fluorescence intensity, long response time and poor stability. Here, a simple and effective film sensor was developed for the visual detection of Cu2+ using quantum dots (QDs) modified by polyethylenimine (PEI) and poly(vinylidene fluoride) (PVDF) by electrospinning and dip-coating methods. QDsr-PEI on the surface of nanofibers could be used as a responsive red fluorescence signal, while the QDsg dispersed in the nanofibers were used as a green background signal. Due to the high Cu2+ binding capacity of PEI and the contrast-color sensitivity of the two kinds of QDs, it realized an obvious fluorescence change from red to green toward Cu2+ in the liquid phase with a short response time of 30 s and a low detection limit of 2 μM by observation. Furthermore, the film exhibited excellent fluorescence stability to a high temperature and UV light, which is beneficial for satisfying much more possible applications. These results demonstrate that the dual fluorescent film sensor has a great potential for the real-time and visual detection of Cu2+.