A simple but efficient fluorescent sensor for ratiometric sensing of Cd2+ and bio-imaging studies

A very simple schiff base fluorescent probe (NIS) was facilely prepared via a one-step, one-pot condensation reaction between 2, 3-naphthalenediamine and imidazole-2-carboxaldehyde. Among common biologically relevant metal ions, NIS can selectively recognize Cd 2+ via ratiometric fluorescence signal. The chelation of NIS with the Cd 2+ ions resulted in a fluorescence enhancement together with a blue shift (˜74 nm) in the emission maxima, presumably due to the combined effects of ICT (internal charge transfer) and CHEF (chelation-enhanced fluorescence). The binding stoichiometry of NIS to Cd 2+ is 1:1 and the fluorescence intensity ratio (F 398 /F 472 ) changes allow a ratiometric detection of Cd 2+ with the detection limit of 3.87 × 10 −7  M. Under fluorescence confocal microscope and via two emission channels, the probe is capable to detect Cd 2+ ions in Human liver cancer cells (SMMC-7721), zebrafish and live tissues of Arabidopsis thaliana, demonstrating its applicability for detecting Cd 2+ ions in different biological context with low toxicity.