Highly Sensitive Detection of Sulfur Ion in Water by Four-Color Fluorescence Based on Cu-Containing Metal–Organic Framework

In this paper, a highly sensitive method for sulfur ion (S²⁻) detection was developed based on a four-color fluorescence probe constructed from copper-containing metal–organic framework (CuBDC) and four dye-labeled single-strand DNA (ssDNA). In the absence of S²⁻, dye-labeled ssDNA can be adsorbed on the surface of CuBDC, and the dyes are close to copper ion on the CuBDC surface, their fluorescence is quenched by copper ion, and their fluorescence signals are weak. In the presence of S²⁻ in the system, S²⁻ reacts with copper ion in CuBDC to form CuS, which has a more stable structure than complex CuBDC, resulting in the decomposition of CuBDC. In this case, dye-labeled ssDNA are detached from the CuBDC surface and dissolved in the solution, and the fluorescence of the dyes is restored. Under the optimized conditions, there is a good linear relationship between the total fluorescence intensity of four dyes and the concentration of S²⁻ in the range of 2 × 10⁻⁹ to 5 × 10⁻⁸ mol/L; the detection limit is 2.2 × 10⁻¹⁰ mol/L. The method has a good selectivity and accuracy, and it can be applied to the analysis and detection of S²⁻ in actual water samples.