Smartphone‐Based Stand‐Alone Colorimetric Sensing of Cobalt(II) by Using Schiff Base Probes

ABSTRACT Cobalt ion, though essential in trace amounts, exerts significant health risks upon excessive exposure. Therefore, the development of simple, efficient, and selective sensors of Co 2+ will find notable applications in environmental and health sectors. In this study, three Schiff base colorimetric probes of Co 2+ ( ST , AT , and DA ) have been reported. These probes exhibited a distinctly visible change in color upon binding with Co 2+ , which enabled naked‐eye detection of the metal ion without using any sophisticated instrument. Further, rapid response, high selectivity, and sensitivity (detection limit as low as 1.18, 0.32, and 0.60 µM for ST , AT , and DA ) of the probes were confirmed. DFT calculations revealed ligand‐to‐metal charge transfer (LMCT) and also an increase in intramolecular charge transfer (ICT) in the probe molecules when complexed with Co 2+ . The practical applicability of the probes was demonstrated through smartphone‐based reliable quantitative and on‐site detection of Co 2+ for environmental and biological monitoring of the metal ion.