The selective recognition of target ions in water is very important and the development of novel water-soluble chemosensor is still an intriguing challenge. Herein, a novel water-soluble fluorescent sensor based on aspartic acid (Asp) functionalized 1,8-naphthalimide derivative (Asp-NI) has been designed and synthesized. The sensor Asp-NI could dissolve in water and successively detect Fe3+ and H2PO4− in water solution with high selectivity and sensitivity. The detection limits are 4.97 × 10−7 mol/L for Fe3+ and 5.27 × 10−6 mol/L for H2PO4−. Other coexistent competitive metal ions (Hg2+, Ag+, Ca2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+, and Mg2+) showed no interference in the Fe3+ detection process. The sensor Asp-NI could act as a Fe3+ and H2PO4− controlled “On–Off–On” fluorescent switch. More interestingly, the Fe3+ induced fluorescence quenching process could be totally reversed by the addition of H2PO4−, this “On–Off–On” switching process could be repeated several times with little fluorescence loss. Notably, the actual usage of sensor Asp-NI was further demonstrated by test kits.
A Water-Soluble Copper-Immobilized Covalent Organic Framework Functioning as an “OFF–ON” Fluorescent Sensor for Amino Acids