A Multiemission MOF-Based Fluorescent Sensor Array Functionalized with pH-Sensitive Dyes for Highly Sensitive Detection and Identification of PFASs

The pollution of per- and polyfluoroalkyl substances (PFASs) is a worldwide concern for the environment and human health due to their large-scale use and persistent polluting property. Therefore, sensitive sensing and discrimination of PFASs in an aqueous system are of great significance. In this work, two zirconium-based metal-organic frameworks (Zr-MOFs), UiO-67-NH₂ and PCN-999, which possess open metal sites, were synthesized by the solvothermal method and acted as hosts for encapsulating pH-sensitive dye molecules. Through an in situ encapsulation strategy, Nile Red and fluorescein isothiocyanate (FITC) were embedded into the nanocages of UiO-67-NH₂, while a rhodamine 6G derivative (RGH) was introduced into the nanocavity of PCN-999. The two yielded fluorescent composites, FR@UiO-67-NH₂ and RGH@PCN-999, exhibited excellent water stability and luminescence persistence, exhibiting triple-emission and dual-emission channels under single-wavelength excitation, respectively. The fluorescent sensor array constructed by these two Dye@MOFs could be applied for the highly sensitive detection and identification of six PFASs based on the differential fluorescence responses. Combined with principal component analysis (PCA) and hierarchical cluster analysis (HCA), this fluorescent sensor array could accurately distinguish six PFASs with concentrations as low as 0.5 μM, and their multicomponent mixtures were also successfully realized, with the limit of detection for individual PFASs as low as 21.8 nM. Additionally, the sensor array demonstrated excellent discrimination and semiquantitative detection of PFASs in complex matrices, including tap water, lake water, and washing liquor from firefighting protective clothing. Powder X-ray diffraction (PXRD), infrared absorption spectrum (FT-IR), and X-ray photoelectron spectroscopy (XPS) further verified that the fluorescent sensor array might involve static fluorescence quenching.