A turn-off fluorescent sensor for detecting Cu2+ based on fluorophore-labeled DNA and polyethyleneimine

A novel sensing system has been designed for the Cu 2+ detection based on the quenched fluorescence signal of 6-carboxyfluorescein (FAM)-labeled DNA/polyethyleneimine. The FAM-labeled DNA showed weak fluorescence at the emission wavelength of 530   nm in a pH 4.8 acetic acid-sodium acetate buffer solution. When the polyethyleneimine was introduced to the FAM-labeled DNA solution, the fluorescence signal was greatly amplified. Subsequently, upon the addition of Cu 2+ , Cu 2+ can be captured by the amino groups of the polyethyleneimine to form an absorbent complex, resulting in a strong quenching of the fluorescence of FAM-labeled DNA/polyethyleneimine via a fluorescence resonance energy transfer effect. Herein, we have demonstrated that this facile methodology can offer a rapid, reliable, and selective detection of Cu 2+ with a detection limit as low as 20   nM and a linear range of 100–1600   nM. Furthermore, the detection results for Cu 2+ in a lake water sample obtained by this sensing system agreed well with that by atomic absorption spectroscopy, suggesting the potential application of this sensing system.