Relative quantitation of metal oxide nanoparticles in a cutaneous exposure model using enhanced darkfield microscopy and hyperspectral mapping

The biological effects associated with the unique properties of engineered nanoparticles (ENPs) remain largely unknown. Animal models of exposure are valuable for assessing potential toxicity and adverse health effects. This study presents a method to determine relative quantitation of nanoparticle (NP) abundance in histological samples in an ex vivo model of cutaneous exposure to metal oxide NPs using enhanced darkfield microscopy (EDFM) with hyperspectral imaging (HSI) and mapping. Porcine skin tissue was topically exposed to alumina, ceria, and silica NPs using a modified Franz diffusion chamber and histologically prepared for imaging. EDFM allowed for rapid direct visualization of NPs, while hyperspectral mapping confirmed the composition of NPs throughout the tissue, based on positive matching of pixels to reference spectral libraries (RSLs). Relative quantitation of NPs was achieved based on calculating the percentage of mapped pixels per field of view (FOV). The greatest abundance of mapped NPs was found in the ceria-exposed group regardless of tissue layer, relative to the other groups. Fewer NPs were found in the dermis compared to the stratum corneum in both the alumina- and ceria-exposed groups. This study demonstrated EDFM-HSI as a valuable method to determine relative quantitation of NPs in histological samples. The methods put forth in this study could be adapted for application to other NP types as well as other biological or environmental matrices.