Colorimetric detection of Fe3+ and Fe2+ and sequential fluorescent detection of Al3+ and pyrophosphate by an imidazole-based chemosensor in a near-perfect aqueous solution

Abstract

A novel chemosensor was designed and synthesized for various analytes: Fe3+, Fe2+, Al3+ and pyrophosphate. The sensor showed a selective color change from yellow to orange toward both Feat and Fe2+ in a near-perfect aqueous solution, which could be reusable simply through treatment with ethylenediaminetetraacetic acid. The detection limits (0.27 mu M and 0.32 mu M) for Fe3+ and Fe2+ were much lower than the environmental protection agency guideline (5.37 mu M) in drinking water. The sensor could be used to quantify Fe3+ in real water samples. Moreover, this sensor acted as a 'turn-on' and 'turn-off type fluorescent sensor toward Al3+ and pyrophosphate. The sensing mechanism of the sensor for Al3+ could be explained by chelation-enhanced fluorescence effect, which was supported by theoretical calculations. Through a metal-complex displacement method, the sensor-Al3+ complex selectively responded to pyrophosphate over various anions especially including phosphate-based anions. Interestingly, the sensor could be used to sequentially detect both Al3+ and pyrophosphate in the living cells.