Optical photothermal infrared spectroscopic assessment of microplastics in tissue models and non-digested human tissue sections

Microplastics (MPs) are environmental contaminants with sizes of the order of less than 5 mm that can enter the human body through inhalation and ingestion. Studies have shown that MPs can pose a threat to human health, and thus evaluation of the presence and potential adverse effects of MPs in tissues is critical. Typical MP studies include enzymatic or chemical tissue digestion that can lead to the loss of some MPs. Moreover, digestion does not allow mapping the location of the contaminant within the tissue architecture. This study aimed to develop a method to evaluate the presence of MPs in histological (thin) sections of tissues without digestion using optical photothermal infrared (O-PTIR) microspectroscopy at sub-micron (500 nm) spatial resolution. Tissue phantoms containing specific amounts and types of MPs and biological tissues were evaluated using polarized light microscopy (PLM) and O-PTIR, and several data analysis approaches were employed to detect MPs in non-digested samples. MPs of sizes from 3 to 85 µm were detected and characterized in tissue phantoms. Furthermore, we detected MPs related to the breakdown products of nylon and cellulose particles in thin sections of biological tissues and discussed obstacles related to the use of database spectra for comparison with O-PTIR spectra, demonstrating the potential of this novel approach and the associated challenges.