Microplastics have caused massive environment concerns over widespread presence and potential health impacts, thus attracting tremendous research efforts in recent years. These solid contaminants are widely reported in aquatic systems and freshwater systems. However, as the nature of mciroplastics and their environment matrices are different, it is challenging but urgent to develop standard detection protocols. Optical spectroscopy methods such as infrared and Raman spectroscopy are often applied to serve the fast identification and quantification purpose, but involving expensive instruments and intensive labour work may limit the use in practical studies. Fluorescent tagging method is an alternative way to achieve reliable results of microplastics abundance, especially for microplastics down to sub-micron range. So far, only Nile Red dye was studied.  This study will report a new and efficient dye for analysis of microplastics in the environmental samples. After filtration, the optimal staining condition, including solvent types, solvent concentrations, dye concentrations, exposure time was investigated under the fluorescent microscope with blue light. Commercial microplastics samples including nylon 6, polyethylene, polyethylene terephthalate, polypropylene, polystyrene and polyvinylchloride can be successfully stained under the optimal condition. To apply this method to environmental samples, H<sub>2</sub>O<sub>2</sub> digestion was performed first to minimize the false positives introduced by natural organic matters and inorganic particles were removed by saturated sodium chloride density separation. The number of fluorescent particles was considered as the microplastics abundance. Recovery rate of spiked polypropylene (100 – 200 µm) and sand samples can reach 95% (by number).  This method yields a more reliable counting results of small microplastics which can not be visually identified and makes fast screening possible. The selected spirooxazine dye exhibits comparable staining efficiency to Nile Red, but higher selectivity and lower cost can make it a more promising dye used in microplastics research.

Fast screening of microplastics abundance by a highly-selective fluorescent dye

256th National Meeting (2018)

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