A dual sensing probe for Cd2+ and Zn2+ detection in water based on tautomerization of acetamidoquinoline containing dipicolylamine and its application in water samples and cell imaging

Abstract

Two novel fluorescent probes (2QAD and 6QAD) for metal ion detection were designed and synthesized based on acetamidoquinoline derivatives containing dipicolylamine unit. 2QAD distinctively exhibits fluorescence enhancement with Cd²⁺ and Zn²⁺ in aqueous media at different emission wavelengths of 350 and 380 nm, respectively. The fluorescence enhancement of 2QAD involves inhibiting the PET process from the dipicolylamine group to the quinoline ring by the corresponding 1:1 complexation with each metal ion. The reversibility of complexes when adding EDTA indicates the static fluorescence-enhancing mechanism. The distinguished fluorescence responses result from amide-imidic tautomerization of 2QAD induced by the complexation with different metal ions, confirmed by ¹H NMR. From the results of fluorescence titration, the LOD values for Cd²⁺ and Zn²⁺ were calculated to be 17 and 8.5 ppb, respectively, with a good linear range. Furthermore, the 2QAD probe can be employed to determine the amount of Cd²⁺ and Zn²⁺ in real water samples and can also be applied to macrophage cell RAW264.7.