A non-fluorescent group-based "off-on-off" chemosensor for detection of Al3+ and Fe3+ and zebrafish bioimaging

The chemosensor <bold>LN</bold> (4-((2-hydroxy-4-methoxybenzylidene)amino)-N-(pyrimidin-2-yl)benzenesulfonamide), containing naphthol OH and imine groups, was synthesised via an amine-aldehyde condensation reaction using sulfadiazine and 4-methoxysalicylaldehyde as starting materials. The sensor was successfully used for the sequential recognition of Al3+ and Fe3+ in aqueous systems (DMSO/H2O (V/V = 9:1)), exhibiting excellent stability, resistance to interference, a fast detection timescale (<1 min), and low detection limits. Under the same conditions, without further preprocessing, the [<bold>LN</bold> + Al3+] system enabled the sequential detection of Fe3+ through fluorescence quenching. The sensing mechanisms of the chemical sensor for specific target ions (Al3+ and Fe3+) and the molar ratios of the resulting complexes were elucidated through Job's plot, H-1 NMR titration studies, and HRMS analyses, with these findings further validated by theoretical calculations. Furthermore, zebrafish bioimaging experiments indicated that the sensor <bold>LN</bold> exhibits favourable membrane permeability.