Design and synthesis of two new terbium and europium complex-based luminescent probes for the selective detection of zinc ions

Zinc plays a key role in many physiological processes and has implications for the environment. Consequently, detection of chelatable zinc ion (Zn²⁺) has attracted widespread interest from the research community. Lanthanide-based luminescent probes offer particular advantages, such as high water solubility, long luminescence lifetimes and a large Stokes’ shift, over common organic dye-based fluorescent sensors. Here, we report the synthesis of terbium and europium complex-based probes, Tb-1 and Eu-1, for sensitive and selective detection of Zn²⁺ in water. These probes featured the incorporation of bis(2-pyridylmethyl)]amine (DPA) receptor for Zn²⁺ chelation and the 1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane (DO3A) ring to chelate lanthanide (Ln³⁺). Tb-1 and Eu-1 displayed high selectivity for Zn²⁺ ions over a wide range of competing ions, with limits of detection of 0.50 ± 0.1 μM and 1.5 ± 0.01 μM, respectively. Density functional theory simulations were in good agreement with experimental observations, displaying high Zn²⁺ selectivity compared with most competing ions. In the competing ions experiments, the luminescence response of Tb-1 and Eu-1 was moderately quenched by some ions such as Cu²⁺, this was linked to the comparable binding abilities of these ions for the receptor of the probe.