Selective and sensitive recognition of Zn²⁺ by a dansyl-derived peptide sensor

A dansyl-derived peptide sensor, Dansyl-HGHW (D₁), was designed and investigated for the selective and sensitive recognition of Zn²⁺. The selectivity of D₁ toward Zn²⁺ among twelve metal ions (Na⁺, K⁺, Ag⁺, Mg²⁺, Ca²⁺, Mn²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Al³⁺, and Fe³⁺) was evaluated using fluorescence measurements at an excitation wavelength of 290 nm, showing a pronounced preference for Zn²⁺. The influence of various Zn²⁺ counterion salts (NO₃ ^-, AcO^-, I^-, SO₄ ^2-, Cl^-, ClO₄ ^-) on the sensing performance of D₁ showed no significant influence. Interference studies indicated that the majority of metal ions did not affect Zn²⁺ detection, except for Ni²⁺ and Cu²⁺, which interfere with the sensing response. pH-dependent fluorescence studies of D₁ in the presence of Zn²⁺ showed that effective Zn²⁺ coordination occurs exclusively above the imidazole's pK _a, under basic conditions (pH 8-12). Binding studies revealed a strong interaction between D₁ and Zn²⁺ with a binding constant of 1.46 × 10⁵ M^-1 and a limit of detection of 47.15 nM. Furthermore, binding interaction analysis using Job's plot indicated the presence of successive 1 : 1 and 3 : 2 metal-to-ligand stoichiometry. Cytotoxicity studies revealed that D₁ is non-toxic to L-929 fibroblast cells over the tested concentration range (12.5-200 µM). Additionally, cell imaging studies have demonstrated the efficacy of D₁ in detecting intracellular Zn²⁺. These results indicate that D₁ is a promising peptide-based fluorescent sensor for selective Zn²⁺ detection.