Polyindole/cadmium sulphide nanocomposite based turn-on, multi-ion fluorescence sensor for detection of Cr³⁺, Fe³⁺ and Sn²⁺ ions

The elevated concentration of heavy metal ions poses severe challenges to environmental homeostasis and human health. Although significant efforts have been made towards the development of heavy metal ion sensors with varying degrees of success, these sensors are largely tailored for, and hence limited to, the detection of a single metal ion. Here we present a novel fluorescence-based sensor featuring polyindole/cadmium sulphide (PIN/CdS) nanocomposite that uniquely detects the presence and concentration of three important heavy metal ions, namely chromium (Cr³⁺), iron (Fe³⁺) and tin (Sn²⁺). The PIN/CdS nanocomposite was found to be an excellent receptor for the target ions via significant fluorescent enhancement owing to the inhibition of internal charge transfer (ICT) process and an efficient chelation enhanced fluorescence (CHEF) effect. A linear relationship between fluorescence intensity and Cr³⁺, Fe³⁺ and Sn²⁺ concentrations was obtained. Importantly, no interference was observed from 17 other commonly tested metal ions thereby making it a highly selective, yet multiplexed, probe for detection of these three ions. Finally, the sensor was used to detect and quantify aforementioned ions in routine drinking water samples. The multiplexed sensing ability and remarkable functional reversibility coupled with its straightforward synthesis and easy-to-use characteristics make this sensor particularly attractive for environmental and biomedical applications.