Label-free G-quadruplex-specific fluorescent probe for sensitive detection of copper(II) ion.

An effective G-quadruplex-based probe has been constructed for rapid and sensitive detection of Cu(2+). In this probe, an anionic porphyrin, protoporphyrin IX (PPIX) served as a reference signal, which binds to G-quadruplex specifically and the fluorescence intensity increases sharply. While, in the presence of Cu(2+), the G-quadruplex can catalyze the related Cu(2+) insertion into the protoporphyrin, the fluorescent intensity is decreased. The fluorescence of the response ligand could be selectively quenched in the presence of Cu(2+) and not interfered by other metal ions. The probe provided an effective platform for reliable detection of Cu(2+) with a detection limit as low as 3.0nM, the high sensitivity was attributed to the strong metalation of PPIX with Cu(2+) catalyzed by G-quadruplex (PS5.M). Linear correlations were obtained over the logarithm of copper ion concentration in the range from 8×10(-9)M to 2×10(-6)M (R=0.998). The G-quadruplex-based probe also could be used to detect Cu(2+) in real water samples. Additionally, these striking properties endow the G-quadruplex-ligand with a great promise for analytical applications.