Nanoscale Fluorinated Carbon Dots for the Detection of Perfluorooctanoic Acid in Aqueous Systems: A Fluorescence Assay Enhanced by Fluorophilic Interactions

Due to the growing demand for per- and poly fluoroalkyl substances (PFAS) detection, analytical methods are progressively focused on developing facile and efficient techniques for detecting PFAS compounds in water systems to eliminate the need for complex procedures. Here, we developed a nanoscale fluorine(F), nitrogen(N)-doped carbon dot-based fluorescence (FL) sensor designed for the sensitive detection of perfluorooctanoic acid (PFOA) in drinking water. To counterbalance the effects of the N/F ratio on fluorophilicity, the synthesis of fluorinated carbon dots (F-CDs) was optimized by examining polyethylenimine (PEI) to tetrafluoroterephthalic acid (TFTA) ratio from 1:3 to 1:10. The highest quantum yield of 10.6% was achieved at a 1:3 ratio. The F-CDs demonstrated a blue fluorescence with optimum excitation and emission wavelengths at 350 and 470 nm, respectively. F-CDs were extensively characterized using fluorine nuclear magnetic resonance (FNMR), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron Spectroscopy (XPS), dynamic light scattering (DLS), and ζ-potential measurements. ζ-Potential analysis confirmed the surface chemistry of the F, N-CDs, as evidenced by their cationic nature. The interaction with the PFOA led to a noticeable decrease in the surface charge of the CD, as evidenced by electrostatic, and fluorophilic interactions. The sensor exhibited high sensitivity and selectivity toward PFOA within the detection range from 10 to 1660 ppt and a low detection limit of 3 ppt. The sensor’s capability to measure PFOA concentrations in groundwaters with high accuracy provides a reliable detection method for safeguarding water resources and public health, making it a valuable tool for environmental monitoring.