A phenazine-imidazole based ratiometric fluorescent probe for Cd²⁺ ions and its application in in vivo imaging

A new phenazine-imidazole based Schiff base (PIS) fluorescent probe has been developed for the ratiometric detection of Cd²⁺ ions in aqueous media at physiological pH. PIS upon binding with Cd²⁺ ions shows red shifted fluorescence and thereby, permits ratiometric detection of Cd(II) ions. A detection limit down to 2.10 × 10^-8 M was determined for Cd²⁺ quantitation. Also, the accompanying apparent fluorescence color change (from yellow to orange red) is noticeable to the naked eye under a UV-lamp. The sensing mechanism could be attributed to the 1 : 1 PIS-Cd complexation, followed by extension of the conjugation due to better planarity and modulation of the charge transfer efficiency in the probe. This was complemented by solvatochromism and density functional theory calculations. Furthermore, PIS was used to detect Cd²⁺ in Oxya chinensis cells, zebrafish larvae and live tissues of Arabidopsis thaliana under a fluorescence microscope, showing great potential in analyzing living biosystems.