A highly selective and sensitive fluorescent chemosensor for distinguishing cadmium(ii) from zinc(ii) based on amide tautomerization

Abstract

A naphthalimide-derived fluorescent sensor termed L2 was designed and synthesized. This sensor showed a highly selective, sensitive, and reversible turn-on response to Cd²⁺ over other metal ions in a wide pH range with a detection limit of 2.35 × 10⁻¹⁰ M. The amide/di-2-picolylamine receptor binds Cd²⁺ in the imidic acid tautomeric form but other metal ions in the amide tautomeric form. Moreover, the sensor can be used to distinguish Cd²⁺ and Zn²⁺ with the naked eye. The Cd²⁺-binding mode and the recognition mechanism of the sensor were investigated using Job's plot, ¹H NMR, HRMS, IR and DFT calculations. Furthermore, the sensor was successfully applied as the active component of indicator papers for on-site detection of Cd²⁺ in pure water and in fluorescence imaging of Cd²⁺ in HeLa cells.