Covalent fluorescence labeling of microplastics via bio-inspired polydopamine bridge: New insights into microplastic...

Facile and rapid fluorescence sensing methods for the accurate detection of microplastics (MPs) in the environment have attracted increasing attention. However, traditional physical staining methods in fluorescence sensing still face challenges in stability and universality. In this study, inspired by the versatile surface adhesion properties of polydopamine (PDA), a PDA-mediated covalent fluorescence labeling (CFL) method was developed for MPs sensing. This CFL method achieves universal labeling of MPs regardless of their chemical and physical characters, thereby overcoming the limitations of conventional physical staining methods. Moreover, the covalent bonding between fluorescein 5-isothiocyanate (FITC) and PDA-MPs fundamentally solves the issue of dye desorption observed in physical staining, maintaining stable fluorescence signals. The CFL sensing method was successfully applied to quantify MPs in practical water samples, and the results were comparable to those of those obtained by traditional Fourier transform infrared spectroscopy, with a relative difference of 4-12%. Additionally, the release profile of MPs from disposable polyethylene gloves under different usage conditions was monitored by the proposed CFL sensing method. It was found that MPs release was significantly enhanced at elevated temperatures or/and in the presence of oil, confirming that the CFL sensing method is an effective tool for tracing MPs pollution sources. Although the developed CFL strategy shares the similar limitations as other existing fluorescence sensing methods for MPs (i.e., lack of polymer compositional identification capacity and microplastic-specific selectivity), it still exhibited promising application potential in source apportionment, environmental monitoring and risk assessment of MPs.