Optical trapping stability of different irregularly shaped microplastic particles

Abstract

Plastic pollution has become a major environmental issue. Waste degrades into microplastics and nanoplastics, which contaminate water, soil, and air, and affect ecosystems and food sources. To elucidate the effects of microplastics on cellular systems, it is essential to comprehend their properties and manipulation at the microscopic scale. This work examines the optical trapping stability of different irregularly shaped laboratory-synthesized, mechanically weathered microplastics: polypropylene (PP), polyethylene terephthalate (PET), and high-density polyethylene (HDPE). We conducted a statistical assessment of optical trapping stability, considering factors such as particle material, color-induced absorption, size, and response to different optical trapping wavelengths (473 nm, 780 nm, and 820 nm). Additionally, we compared these results with the predicted optical trapping stability, simulated for particles with two types of spheroidal shapes. Our results indicate that non-spherical PP microplastics exhibit the highest stability in a single-beam optical trap, while PET microplastics demonstrate the lowest stability. The optical trapping stability of PP and HDPE microplastics is relatively size-independent; however, PET particles larger than 10 μm are three times less likely to be stably trapped than smaller particles. Furthermore, non-transparent materials with higher absorption rates cause less stable optical trapping of microplastics for all three material types. The insights gained regarding the optical properties of irregularly shaped microplastics will help future research on the optically controlled interactions of naturally occurring microplastics with cells and microorganisms at the single-cell level.