A facile switch-on fluorescence sensing method for detecting phosphates from complex aqueous samples

Phosphates play an essential role in our living systems. Therefore, it is important to have simple and effective methods to detect and monitor the level of phosphates in complex samples. In this study, a facile switch-on fluorescence sensing method is developed for the detection of phosphates. The sensing probes are composed of Gd3+ and riboflavin-5′-phosphate (RFMP), which are hard acid and hard base, respectively. Gd3+ and RFMP can strongly bind via chelation once mixed. RFMP emits bright green fluorescence under ultraviolet (UV) light illumination. However, its fluorescence is quenched in the presence of Gd3+, presumably due to aggregation caused quenching. In the presence of phosphates, the fluorescence derived from RFMP on the Gd3+-RFMP can be restored owing to the competitive binding of phosphates with Gd3+ on the Gd3+-RFMP conjugates to release RFMP. In this study, we demonstrate the feasibility of using the developed sensing method to determine the level of phosphates from real world samples such as drinking water and fetal bovine serum under the illumination of a UV lamp (λmax = 365 nm) simply with the naked eye. The lowest distinguishable concentration of using our detection method towards adenosine triphosphate and pyrophosphate with the naked eye is ∼1 μM. Furthermore, when fluorescence spectroscopy is used as a detection tool, the limit of detection has further reduced to ∼611 nM. The feasibility of using the developed sensing probes combined with fluorescence spectroscopy for quantitative analysis of phosphates in real samples is also demonstrated in this study.