A versatile and innovative fluorescent staining reagent for identification of nine types of microplastics: Applications to environmental waters, soil, milk, and biological systems

Microplastic specific staining agent, HTPQ (9-((E)-(((E)-1-(1-hydroxynaphthalen-2-yl)ethylidene)hydrazineylidene)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol), was applied for selective detection of nine types of microplastics (MPs; LDPE, PU, PA, PP, HDPE, PET, PVC, MDPE, and PAN) over non-plastic compounds in deionized water (DIW). HTPQ selectively stained MPs within just 15 min, facilitating their precise and efficient identification with strong green fluorescence. The interaction process between HTPQ and MPs involved the adsorption of HTPQ on MPs, which was demonstrated through X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and field emission scanning electron microscopes (FE-SEM). HTPQ efficiently stained MPs without any effect in the size, aging and pH conditions. The real-world plastic products were also successfully stained by HTPQ. Notably, HTPQ selectively stained MPs over non-plastic particles in environmental samples (stream water, seawater and soil) without the need for pre-treatments. HTPQ demonstrated the ability to detect MPs in milk, highlighting its potential application for identifying MPs within various food samples. Furthermore, the HTPQ-labeled MPs provided an effective method for monitoring the distribution and deposition of MPs in a biological system such as live zebrafish.