Highly sensitive and quantitative detection of phosphate ions in aqueous solutions using a tricolor fluorescent probe based on bimetallic organic framework nanomaterials†

Excessive phosphate content in water can lead to eutrophication, causing massive algal growth and severely damaging aquatic ecosystems. Therefore, developing a simple and sensitive method for detecting phosphate ions is of great significance. In this study, we constructed a tricolor fluorescence probe based on bimetallic organic framework nanomaterials containing copper and zirconium (Cu/Uio-66) and single-stranded DNA of arbitrary sequences labeled with three different fluorescent dyes. A novel, highly sensitive quantitative method for the detection of phosphate ions (PO₄³⁻) was developed. In the absence of PO₄³⁻, dye-labeled DNA is adsorbed on the surface of Cu/Uio-66, and its fluorescence is quenched via a photoinduced electron transfer (PET) mechanism, resulting in a weak fluorescence signal. PO₄³⁻ reacts with Zr⁴⁺ and Cu²⁺ to form copper phosphate and zirconium phosphate, leading to the dissociation of Cu²⁺ and Zr⁴⁺ from Cu/Uio-66, then causing the disintegration of Cu/Uio-66. Dye-labeled DNA dissociates from the surface of Cu/Uio-66 and enters the solution, and the fluorescence of the dye is restored. The optimal conditions for detecting PO₄³⁻ using this probe are as follows: a reaction time of 40 minutes, a reaction temperature of 30 °C, a buffer system pH of 7.7, and a NaCl concentration of 30 mmol L⁻¹ in the buffer system. Within the concentration range of 1.20–150 nmol L⁻¹, the total fluorescence intensity of the three dyes FAM, TAMRA, and Cy-5 exhibited a strong linear relationship with PO₄³⁻ concentration. The linear regression equation fitted between fluorescence intensity (F) and PO₄³⁻ concentration (x) is as follows: F = 29.1684x + 215.9763 (R² = 0.9996), and the detection limit is 0.71 nmol L⁻¹ (n = 9, 3σ). This method has excellent selectivity, with sample recovery rates ranging from 97% to 103%, and it can be used for the detection of PO₄³⁻ in real water samples.