Preparation of irregularly shaped, nano-sized, fluorescent microplastic particles for tracing cellular uptake

Abstract

Microplastics (MPs) are widely distributed; however, their behaviour in the environment and within biological tissues remains unclear. Concerns regarding their health risks have outpaced the elucidation of the true impacts of MPs. Previous studies have indicated that the toxicity of MPs depends on their size. However, toxicity assessments have mainly focused on uniformly sized, spherical polystyrene beads. Therefore, in this study, we developed a simple method for preparing irregularly shaped, nano-sized, fluorescent MP model particles. Fluorescence was incorporated by loading Nile red dye into plastics with various chemical compositions. Aqueous solution of bovine serum albumin (BSA) and chloroform solution of Nile red were added to solutions of polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET) fragmented to nanoscale via solvent-assisted degradation in an organic solvent. Subsequently, model particles of MPs with diameters of 80–250 nm were obtained by volatilising the organic solvent. The BSA functioned as a weak surfactant to prepare irregularly shaped, nano-sized MP particles. Organic solvents with solubility parameters close to those of the plastic materials proved useful for fragmenting durable solvent-treated plastic polymers. Experiments using Nile red incorporated into PP, PE, and PET yielded model particles of PP, PE, and PET that emitted fluorescence at 580–620 nm under 550 nm excitation. The fluorescence of Nile red-loaded nano-MP particles enabled microscopic observation of their cellular uptake. The method presented herein for fabricating fluorescent nano-MP particles using albumin will contribute to further comparative studies of environmental and in vivo MP behaviours.