Dual-channel fluorescence dye: Fluorescent color-dependent visual detection of microplastics and selective polyurethane

In this study, we developed a dual-channel fluorescent dye ((E)-N'-(4-(diphenylamino)benzylidene)pyrazine-2-carbohydrazide) DPC for visual detection of 8 types of microplastics (MPs; HDPE, MDPE, LDPE, PET, PU, PVC, PS, and PP) and selective PU. The intramolecular charge transfer (ICT) and aggregation-induced emission (AIE) properties of DPC were demonstrated by the spectroscopic analysis, DFT calculations, and Tyndall effect. MPs and nonplastics (cellulose, chitin, sand, shell, and wood) were stained with DPC in water and their respective fluorescence signals in the blue and green channels were analyzed. The staining procedure using DPC was optimized with the concentration of DPC and staining time as parameters. DPC was able to effectively stain 8 types of MPs and only PU in blue and green fluorescence signals, respectively. Furthermore, false positive detections of DPC were minimized through additional ethanol treatment after staining. Moreover, the effects of temperature, pH, and salinity on the staining ability of DPC were investigated. Surprisingly, DPC was able to selectively detect PU through the green fluorescence signal even in a single environment where various MPs existed. Most importantly, DPC is the first fluorescent dye capable of selectively monitoring PU in the green channel as well as staining 8 types of MPs in the blue channel. DPC showed promising potential to be used for MP monitoring on real environmental samples.