Enhanced long-term stability of stained microplastics with carbon nitride fluorescent polymer for tracking

Fluorescent labeling and imaging is a useful tool to track the temporal and spatial distribution of microplastics (MPs) with size and shape features. However, the limited fluorescently labeled MPs spheres, photo-bleaching and leaching of organic small molecular dyes hamper the tracking of MPs in the environment. In this work, phenyl-modified carbon nitride (PMCN) fluorescent polymer was prepared and applied for the staining of eight different types of MPs. The interface interaction mechanism between PMCN fluorescent polymer and MPs was investigated by the desorption experiments. The long-time photo-stability of the stained MPs against ultraviolet (UV) light irradiation, freeze-thaw cycles, various environmental factors and real environmental water samples was evaluated. The MPs stained with PMCN fluorescent polymer showed more robust stability than the common dye (Nile red) against the damage when exposure to UV light for 72 h, treatment with freeze-thaw cycles for 60 days, exposure to strong acid, strong alkali, high salinity, freshwater (river and lake) or seawater for 60 days. Results indicate PMCN fluorescent polymer is promising as a convenient, efficient and universal fluorescent tracer for visually tracking the migration and distribution of MPs in environmental water system.