A cost-effective and efficient fluorescence staining agent for the identification of microplastics in environmental samples and zebrafish (Danio rerio)

Microplastics (MPs) are recognized as a significant environmental hazardous material. Therefore, identifying and tracking microplastics are crucial to understand their harmfulness. Herein, we introduce (Z)-N'-(pyren-1-ylmethylene)pyrazine-2-carbohydrazide (PPC) as a cost-effective and efficient fluorescence staining agent. Unique properties of PPC, including aggregation-induced emission (AIE) and solvatochromism, were verified by spectroscopic studies and theoretical calculations. PPC selectively stained eight types of MPs with green fluorescence in water/tetrahydrofuran (THF) solution (97/3, v/v). Interestingly, only polyurethane (PU) was selectively stained both in green and blue channel using 50 % ethanol (EtOH) treatment. Moreover, with 30 % EtOH treatment, PU and polyethylene terephthalate (PET) were distinctly stained in the blue channel, highlighting their selective fluorescence. These results suggested that changes in solvent polarity induced by different EtOH amounts might alter the binding strength between PPC and MPs, resulting in varying fluorescence responses. In addition, the adsorption interaction of PPC to MPs was proposed, based on thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and non-covalent interaction (NCI) analysis. PPC could identify MPs without any influence in the size, aging and pH difference. Successfully, PPC could stain eight types of MPs and selectively PU and PET in artificial environmental samples like seawater, river water and soil. Moreover, PPC-labeled MPs could be tracked in biological system such as Danio rerio (zebrafish) to monitor the transit and accumulation of MPs. These results underscore the potential of PPC for efficient detection of MPs in environmental and biological systems.