A single fluorescent chemosensor for multiple targets of Cu²⁺, Fe^2+/3+ and Al³⁺ in living cells and a near-perfect aqueous solution

A sulfonate-based chemosensor 1 was designed and synthesized for sensing various analytes: Cu²⁺, Fe^2+/3+ and Al³⁺. Sensor 1 showed a high selectivity and sensitivity for the analytes in a near-perfect aqueous medium. Cu²⁺ and Fe^2+/3+ could be monitored by fluorescence quenching of 1. It had sufficiently low detection limits (1.25 μM for Cu²⁺ and 3.96 μM for Fe³⁺), which were below the recommended levels of the World Health Organization for Cu²⁺ (31.5 μM) and the Environmental Protection Agency for Fe³⁺ (5.37 μM). 1 showed the high preferential selectivity for Cu²⁺ and Fe³⁺ in the presence of competitive metal ions without any interference. Importantly, pyrophosphate could be used to distinguish Fe³⁺ from Cu²⁺. In addition, this sensor could monitor Al³⁺ through fluorescence emission change. Moreover, 1 was successfully applied to quantify and image Al³⁺ in water samples and living cells. Based on photophysical studies and theoretical calculations, the sensing mechanisms of 1 for Cu²⁺ and Al³⁺ were explained, respectively.