Europium–Pyridinedicarboxylate–Adenine Light-Up Fluorescence Nanoprobes for Selective Detection of Phosphate in Biological Fluids

Phosphate (Pi) plays important roles in various physiological processes. Its quantification in biological fluids is highly crucial for timely warning of Pi accumulation. Herein, an europium (Eu)-based coordination polymer nanoprobe (Eu/DPA/Ade) is prepared by coordinating 2,6-pyridinedicarboxylic acid (2,6-DPA) and adenine (Ade) with Eu3+. Eu/DPA/Ade exhibits light-up fluorescence response to Pi. The strong coordinating interaction between Eu3+ and O atoms in the Pi group not only shortens the Eu3+-ligand distance to improve the energy transfer from 2,6-DPA to Eu3+ but also attenuates the fluorescence quenching from water molecules in the coordinating sphere of Eu3+. Eu/DPA/Ade produces red emission at λem 618 nm via the "antenna effect". The coligand Ade further promotes the fluorescent emission. The selective recognition of Pi within 10–60 μM is achieved with a detection limit of 4.65 μM. In addition, a certain level of Pi (100–170 μM) causes an exponential increment on the fluorescence of Eu/DPA/Ade and makes it feasible for visual estimation of Pi under irradiation by an ultraviolet lamp at 254 nm. The quantitative detection and visual estimation of Pi in human urine and saliva have been demonstrated.