Ratiometric Fluorescence Assay for Pyrophosphate Based on Sulfur Nanodots Decorated Metal-Organic Frameworks

Selective and sensitive detection of inorganic pyrophosphate (PPi) are of great significance both for clinical applications and fundamental research. In this work, a ratiometric fluorescent probe was developed by decorating a porphyrin-based metal-organic framework (PCN-224) with sulfur nanodots (S-dots). The red-fluorescence of PCN-224 was significantly promoted (more than 6-fold) by S-dots through inhibiting molecular motion of porphyrin ligand, which also provided active sites for the detection of Cu²⁺ and PPi. Cu²⁺ could selectively quench the red-fluorescence of PCN-224 through coordination with porphyrin ligand, and the competition reaction between PPi and Cu²⁺ resulted in the decomposing of coordination and recovery of red-fluorescence. The blue-fluorescence from S-dots was deemed as effective reference, which provided a built-in correction in complex environments. Based on these photophysical properties, a ratiometric fluorescence assay was developed for the quantitative detection of Cu²⁺ and PPi, with a limit of detection of 0.11 and 2.66 μM, respectively. The accuracy and practical applications of assays were also demonstrated by detection in tap water and human serum samples.