A ‘turn-on’ fluorescent sensor for the selective detection of cobalt and nickel ions in aqueous media

Two newly designed turn-on fluorescein-based chemosensors are highly sensitive and selective for Co2+ and Ni2+ in both absorption and emission modes, normally difficult to achieve with these paramagnetic ions. Binding to both ions is reversible, as indicated by the bleaching of the color when the metal is extracted with EDTA. Given the difficulty of designing enhanced fluorescent sensors for paramagnetic Co2+ and Ni2+ ions, the fluorescein compounds may inspire the further development of more sophisticated sensing constructs for the detection of these ions.