A multiple target chemosensor for the sequential fluorescence detection of Zn²⁺ and S²⁻ and the colorimetric detection of Fe^3+/2+ in aqueous media and living cells

A novel multiple target sensor, (E)-5-((4-(diethylamino)-2-hydroxybenzyldene)amino)-1H-imidazole-4-carboxamide (DHIC), was synthesized for fluorescence detection of Zn²⁺ and S²⁻ and colorimetric detection of Fe^3+/2+ in aqueous media. DHIC can operate as a turn “on-off” sequential fluorescent sensor for Zn²⁺ and S²⁻. Detection limits (1.59 μM and 8.03 μM) for Zn²⁺ and S²⁻ are below the WHO standards (76.0 μM and 14.7 μM). The DHIC-Zn²⁺ complex could be reversibly reused with ethylenediaminetetraacetic acid. Importantly, DHIC could image sequentially Zn²⁺ and S²⁻ in living cells. Moreover, DHIC displayed a discriminatory color change from pale yellow to orange yellow to Fe^3+/2+. The detection limit of DHIC for Fe^3+/2+ (0.73 μM and 1.11 μM) is far below the EPA drinking water standard (5.37 μM). The sensor DHIC could be applied to analyze Fe³⁺ in real samples.