A novel red-emissive fluorescent dye for the selective detection of polyurethane in environmental matrices; river, sea, and soil

A novel red-emissive fluorescent dye, DBD was developed to detect selectively polyurethane (PU) microplastics (MPs). The solvatochromic properties and aggregation-induced emission (AIE) behavior of DBD were illustrated using spectroscopic studies and density functional theory (DFT) calculations. The optimized staining conditions for selective PU staining were determined by evaluating three parameters: staining time, solvent composition, and dye concentration. Under the optimized conditions (75 μM for 60 min in a 1:1 (v/v) mixture of deionized water/ethanol (DIW/EtOH)), DBD selectively stained PU MPs among eleven types of MPs (PU, low-density polyethylene (LDPE), polyacrylonitrile (PAN), medium-density polyethylene (MDPE), polycarbonate (PC), polypropylene (PP), polystyrene (PS), polyamide (PA), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and high-density polyethylene (HDPE)) and five types of natural particles (sand, chitin, shell, cellulose, and wood). In addition, DBD successfully stained PU MPs of various sizes as well as aged PU MPs, and maintained staining performance in pH conditions ranging from 5 to 9. Moreover, DBD selectively stained PU MPs in complex environmental matrices like river water, seawater, and soil without requiring special pretreatment, allowing clear discrimination from other particles through red fluorescence. The interaction of DBD and PU was suggested to be adsorption via hydrogen bonding and van der Waals interaction, which was analyzed using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), non-covalent interaction (NCI), and X-ray photoelectron spectroscopy (XPS).