Use of carbon quantum dots and fluorescein isothiocyanate in developing an improved competitive fluoroimmunoassay for detecting polybrominated diphenyl ether

Polybrominated diphenyl ethers (PBDEs) are used as a flame retardant in a wide variety of consumer products. Once released into the environment, PBDEs are characterized as Persistent Organic Pollutants that have an affinity for bioaccumulation, resulting in humans and the ecosystem suffering ill health effects upon exposure. In this work, two strategies are proposed to detect PBDEs using competitive fluoroimmunoassay (FIA). To develop a competitive FIA of PBDEs, a model PBDE compound, 2, 3', 4, 5', 6-pentabromodiphenylether (BDE-121), was selected for antibody development, and a monoclonal antibody against BDE-121 was prepared, via hapten synthesis, in our laboratory. Carbon quantum dots (CQDs) and fluorescein isothiocyanate (FITC) were employed as fluorescent labels to produce the FIA. Experimental results showed that the bioconjugates CQDs-BSA-BDE-121 and FITC-BSA-BDE-121 both demonstrate good sensitivity and selectivity for detecting BDE-121 and are therefore both effective strategies. However, it was also determined that CQDs performed better than the FITC, likely due to their superior biocompatibility and photostability, displaying a linear range of 0.5 nM-100 nM (0.28 ng/mL similar to 56.47 ng/mL) with a limit of detection of 0.1 nM (0.056 ng/mL). Thus, this study confirmed the potential of combining carrier protein/haptens with biologically modified QDs to detect small analytes. Finally, CQDs and FITC were shown to be a good-quality donor/acceptor pair for Fluorescence Resonance Energy Transfer (FRET), which will provide a path and foundation for researching FRET based on CQDs and FITC for PBDE detection and quantification.