Label-Free Identification and Imaging of Microplastic and Nanoplastic Biouptake Using Optical Photothermal Infrared Microspectroscopy

As plastic waste breaks down into smaller fragments in the environment, it poses a significant threat to both terrestrial and aquatic ecosystems as well as exposed humans via contaminated water, air, and food. There is thus a critical need to understand the biological uptake and subsequent impacts of plastic particles in aquatic and terrestrial organisms. Yet, we lack effective and robust methodologies to identify and localize micrometer and nanometer-sized polymer particles in whole organisms. This proof-of-concept study introduces a label-free approach for the localization and identification of plastic particles within organisms utilizing optical photothermal infrared microscopy (O-PTIR) and microtome techniques. By integrating O-PTIR imaging with microtomy, we achieved high spatial resolution and sensitivity, allowing us to detect and identify different plastic particles (polystyrene, polyethylene, polypropylene, and poly(methyl methacrylate)) and confirm their localization in a tissue sample. The results demonstrate successful visualization of microplastics and nanoplastics at moderate exposure concentrations in a range of aquatic and terrestrial organisms; namely, <i>Daphnia magna</i>, <i>Drosophila melanogaster</i>, and <i>Eisenia andrei</i>. By eliminating the need for labeling and offering submicron resolution, this vibrational microspectroscopy-based approach emerges as a promising tool for advancing our understanding of the distribution and potential impacts of microplastics and nanoplastics.