A simple benzothiazolium-based sensor for cyanide detection: Applications in environmental analysis and bioimaging.

A new sensor based on Ethylbenzothiazolium-2-hydroxynaphthaldehyde conjugate-based fluorescent sensor, (E)-3-ethyl-2-(2-(2-hydroxynaphthalen-1-yl) vinyl) benzo[d]thiazol-3-ium iodide (SU-1) was designed and synthesized. The structure of SU-1 was confirmed by H NMR, C NMR, HRMS, and single crystal XRD spectral analysis. SU-1 displayed a colorimetric and fluorometric response in a DMSO:HO (1:1,v/v) matrix, changing color from pale yellow to colorless visible to the naked eye, accompanied by a ∼ 120 nm red-shift in the absorption spectra upon CN addition. This shift, due to formation of deprotonation followed by the nucleophilic attack on the benzothiazolium ring's double bond, disrupts π-conjugation, blocking intramolecular charge transfer within SU-1. However, competitive anions showed negligible interference while detecting CN. The Limit of detection for CN was determined to be 0.27 nM, significantly below the WHO's permissible CN concentration in drinking water (1.9 μM). Job's plot analysis shows that the binding stoichiometry of SU-1 to CN is a 1:1, with a stability constant (Ka) of 1.58 x 10 M. The sensor demonstrated practical applications in environmental water samples and fluorescence imaging of intracellular CN in CAD cell line.