Fluorescent Sodium Alginate Hydrogel–Carbon Dots Sensor for Detecting Perfluorooctanoic Acid in Potable Water

Per- and polyfluoroalkyl substances (PFASs), especially perfluorooctanoic acid (PFOA), are emerging environmental and health concerns due to their persistence, resistance to degradation, and bioaccumulation. In this study, we developed a sensitive and selective detection platform based on a sodium alginate (SA) hydrogel modified with nitrogen and fluorinated carbon dots (N,F-CDs) to enhance the detection of PFOA in natural and engineered water systems. The SA hydrogel–N,F-CD composite exhibited strong fluorescence at 480 nm after optimization, achieving a detection limit as low as 0.001 ppt. The sensor was characterized by using Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FT-IR), Powder X-ray Diffraction (PXRD), X-ray Photoelectron Spectroscopy (XPS), and zeta potential spectroscopy, revealing its structural integrity, functional groups, and the surface charge of the SA hydrogel–N,F-CDs network. Sensitivity assessments demonstrated a linear fluorescence response to PFOA concentrations ranging from 1 to 66 ppq. Selectivity tests confirmed the sensor’s ability to distinguish PFOA from other perfluorinated compounds, with minimal interference from other substances. The practical applicability of the sensor was validated using spiked recovery experiments with tap water samples from various locations, achieving recovery rates between 94% and 106.6%. This sensor offers a reliable, efficient, and highly sensitive platform for the detection of PFAS, demonstrating its potential for real-world PFAS-monitoring applications.