Ratiometric fluorescent sensing of phosphate ion in environmental water samples using flavin mononucleotide-functionalized Fe3O4 particles

Phosphate ion (POq-) serves as an important nutrient carrier to support the growth of aquatic animals and plants in aquatic systems. However, excess concentrations of POq- are the key factor responsible for eutrophication, resulting in rapid deterioration of water quality. Therefore, accurate determination of POq- is of great significance in water quality and security. In this study, flavin mononucleotide (FMN), an intracellular form of vitamin B2, was used as fluorophore. A novel off-on fluorescent sensing platform (FMN@Fe3O4) was fabricated for selective and sensitive detection of POq-, and showed excellent fluorescence response and good selectivity for POq- detection. With the addition of POq-, the fluorescence intensity restored is proportional to POq- concentration in the quantification range of 50 nM-0.75 mu M with a limit of detection as low as 20 nM (0.62 mu g.L-1, calculated by P element). An adsorption/ desorption sensing mechanism via an in-depth analysis of the interfacial interaction between POq- and FMN@Fe3O4 is proposed. FMN is first adsorbed by its terminal phosphate group on Fe3O4 particles to quench fluorescence. Free POq- replaces the adsorbed FMN and restores the quenched fluorescence to achieve the aim of POq- detection. In addition, this sensing system has been successfully validated in real water sample analysis and all reagents involved are nontoxic, environmentally benign, and easily-available. Therefore, this assay has great applicability in water quality monitoring.

Automated summary

Phosphate ion plays a vital role as a nutrient carrier in supporting the growth of aquatic animals and plants. However, excessive concentrations of phosphate ion can lead to eutrophication and deteriorate water quality. Accurate determination of phosphate ion concentration is crucial for water quality and security. In this study, a novel off-on fluorescent sensing platform using flavin mononucleotide was developed for selective and sensitive detection of phosphate ion, demonstrating excellent fluorescence response and good selectivity. The proposed mechanism involves the adsorption and desorption of flavin mononucleotide on Fe3O4 particles, which is replaced by free phosphate ion to restore fluorescence. The developed sensing system has been successfully validated in real water sample analysis and offers great applicability in water quality monitoring.