Selective detection and tracking of polyamide microplastic by aggregation-promoted fluorescent dye in environmental samples, milk and live organisms

An aggregation-induced emission (AIE)-active staining dye, HMPC ((E)-N′-((2-hydroxynaphthalen-1-yl)methylene)pyrazine-2-carbohydrazide) was developed for selective detection of polyamide (PA) microplastics at a low cost. The unique photophysical property of AIE for HMPC was verified using spectroscopic analysis. The staining efficiency using HMPC was assessed by examining variations in the solvent composition, concentration of HMPC, and staining duration to optimize selective PA staining. By emitting green fluorescence, the optimized HMPC-staining method presented remarkable selectivity for PA compared to ten other kinds of microplastics and five kinds of non-plastics. Based on the results from thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses, the staining process was proposed to be an adsorption between HMPC and PA. Additionally, the analysis of non-covalent interactions (NCI) revealed the importance of van der Waals interactions and intermolecular hydrogen bonds in the adsorption process. HMPC could reliably detect PA under various conditions, including different PA sizes, aged PA, and variation in solvent pH. Importantly, the HMPC staining technique could selectively monitor PA in varied environmental samples like seawater, river water, and soil, without any pretreatment procedure. In addition, HMPC successfully detected PA in milk, demonstrating its potential application for identifying PA contamination in food products. Moreover, the HMPC-labeled PA offered a cost-effective approach to track the distribution and deposition of PA in live zebrafish and brine shrimp.