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 Cu2+. 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 Cu2+, the G-quadruplex can catalyze the related Cu2+ insertion into the protoporphyrin, the fluorescent intensity is decreased. The fluorescence of the response ligand could be selectively quenched in the presence of Cu2+ and not interfered by other metal ions. The probe provided an effective platform for reliable detection of Cu2+ with a detection limit as low as 3.0 nM, the high sensitivity was attributed to the strong metalation of PPIX with Cu2+ 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 Cu2+ in real water samples. Additionally, these striking properties endow the G-quadruplex-ligand with a great promise for analytical applications.

► A novel sensitive G-quadruplex-based probe for Cu2+ was developed.
► The probe was based on Cu2+-induced fluorescence quenching.
► This probe is simple and cost-efficient in designing and operation.
► The detection limit can be down to 3.0 nM.
► The probe could be used to detect Cu2+ in real water samples.