A highly sensitive benzimidazole-based chemosensor for the colorimetric detection of Fe(II) and Fe(III) and the fluorometric detection of Zn(II) in aqueous media

A new dual chemosensor 1 for the colorimetric detection of Fe^2+/3+ and the fluorometric detection of Zn²⁺ has been developed and characterized. The sensor 1 has proven to be highly selective to Fe^2+/3+ with a color change from colorless to dark green in a near-perfect aqueous solution. 1 had low detection limits (1.21 μM for Fe³⁺ and 1.18 μM for Fe²⁺), which are lower than the World Health Organization guideline (5.36 μM) for drinking water. Moreover, 1 showed a selective detecting ability for Zn²⁺ by 'OFF-ON' fluorescent response in aqueous solution. The detection limit (1.05 μM) of 1 for Zn²⁺ was much lower than World Health Organization guideline (76 μM) for drinking water. Interestingly, it could be recycled simply through treatment with an appropriate reagent such as EDTA (ethylenediaminetetraacetic acid). The sensing mechanism of 1 for Zn²⁺ was explained by the theoretical calculations. In particular, the sensor 1 could be used to quantify iron and zinc in water samples.