Development of a Microfluidic Ion Current Measurement System for Single-Microplastic Detection

Microplastics (MPs) can adsorb heavy metals and metalloids and may cause a potential health hazard. Precise measurements of their size, shape, composition, and concentration at a single-MP level are important to evaluate their potential toxicity and identify their original source. However, current single-MP analytical methods such as micro-Raman spectroscopy and scanning electron microscopy have low throughput. Therefore, in this study, we applied the ion current sensing method, which has been used for single cell analysis, to single-MP analysis and examined whether size measurement and composition analysis of MPs at the single particle level are possible. In singleMP measurements, plastic particles must be monodispersed in solution at least within the measurement time. The agglomeration behavior was carefully observed after adding sodium dodecyl sulfate to trisborate-EDTA buffer at 2–16 mM. Under these conditions, the size of polystyrene beads could be measured using the ion current sensing under the monodispersed condition. Next, ion current sensing was performed on four pseudo MPs fabricated from different materials (polyethylene, polyethylene terephthalate, polypropylene, and polyvinyl chloride) that were mechanically grazed and UV-irradiated to imitate real marine MPs. Although significant differences in the ion current signals from different material MPs were not observed, fast (100 MPs within 2 s) and precise measurements in the MPs’ sizes at a single-MP level were successfully achieved.