Ratiometric detection of Cu+ in aqueous buffered solutions and in live cells using fluorescent peptidyl probe to mimic the binding site of the metalloprotein for Cu+

Ratiometric detection of Cu+ in aqueous buffered solutions and live cells is highly recomended. We synthesized a fluorescent probe (1) based on the peptide receptor to mimic the binding site of the metalloprotein (CusF) for Cu+. 1 sensitively and selectively detected Cu+ among various biological relevant metal ions in aqueous solutions at physiological pH through a ratiometric response. Job's plot analysis indicated that 1 formed a 2:1 complex with Cu+ and the binding affinity of 1 for Cu+ was measured to be 5.73 × 10−21 M2 from a competition experiment with bathocuproine disulfonate. The probe showed significant ratiometric responses to Cu+ over a wide range of pH (6.5 ∼ 10.5). The binding mode study showed that the imidazole and indole groups of the peptide receptor played a critical role in the tight binding to Cu+. 1 penetrated successfully in living A549 cells and detected intracellular Cu+ ions in Golgi apparatus through ratiometric response. Giving the recent growing interests in fluorescent imaging of Cu+, the development of a fluorescent ratiometric probe (1) based on the peptide receptor to mimic the binding site of the metalloprotein for Cu+ will provide a potential tool for detection of intracellular metal ions in live cells.