A Ratiometric Fluorescence Probe for Visualized Detection of Heavy Metal Cadmium and Application in Water Samples and Living Cells

Heavy metal cadmium (II) residuals have inflicted severe damage to human health and ecosystems. It has become imperative to devise straightforward and highly selective sensing methods for the detection of Cd²⁺. In this work, a ratiometric benzothiazole-based fluorescence probe (<b>BQFA</b>) was effortlessly synthesized and characterized using standard optical techniques for the visual detection of Cd²⁺ with a change in color from blue to green, exhibiting a significant Stokes shift. Moreover, the binding ratio of <b>BQFA</b> to Cd²⁺ was established as 1:1 by the Job's plot and was further confirmed by FT-IR and ¹HNMR titrations. The ratiometric fluorescence response via the ICT mechanism was confirmed by DFT calculations. Furthermore, the limit of detection for detecting Cd²⁺ was determined to be 68 nM. Furthermore, it is noteworthy that <b>BQFA</b> showed good performance in real water samples, paper strips, smartphone colorimetric identification, and cell imaging.