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.
We developed a new quantitative detection method for trace sulfur ions (S 2− ) in water using a Cu-containing metal–organic framework material (CuBDC) and 6-carboxyfluorescein group (FAM)-labeled DNA of arbitrary sequence. Without S 2− in the system, the FAM-labeled DNA can be adsorbed on the CuBDC surface through π–π stacking, hydrogen bonding, and van der Waals forces, and then the fluorescent dye FAM is near the Cu 2+ on the CuBDC surface, and the fluorescence of FAM is quenched by a photoinduced electron transfer mechanism between Cu 2+ and FAM. With S 2− in the system, S 2− reacts with Cu 2+ in CuBDC to form the more structurally stable compound CuS, leading to CuBDC decomposition, and the FAM-labeled DNA detaches from the CuBDC surface and the fluorescence of FAM recovers. The quantitative detection of S 2− is realized according to the change in FAM fluorescence intensity. Under optimized conditions, a good linear relationship holds between the fluorescence intensity (F i ) of FAM and the concentration ( C i ) of S 2− in the range of 2–120 nmol/L, and the detection limit is 1.5 nmol/L (3 σ, n = 9). The method has good selectivity and accuracy, and it can be applied to rapidly and accurately analyze S 2− in real water samples.
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