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 single-MP measurements, plastic particles must be mono-dispersed in solution at least within the measurement time. The agglomeration behavior was carefully observed after adding sodium dodecyl sulfate to tris-borate-EDTA buffer at 2–16 mM. Under these conditions, the size of polystyrene beads could be measured using the ion current sensing under the mono-dispersed 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.