Chapter 6: Surface Adsorbates on Nanomaterials and Their Possible Roles in Host Inflammatory and Toxicological Processing

Surface characteristics of nanomaterials are well recognized to contribute prominently to their unique properties and applications. It is less appreciated that the same surfaces have high intrinsic reactivities, typically distinct from identical bulk material chemistries. These size-dependent properties facilitate rapid, ubiquitous surface adsorption and contamination from many sources: storage containers; nanosynthesis components, by-products, and stabilizers; ubiquitous and adventitious environmental pollutants in clean room air and water; and diverse biomolecules that nanomaterials might encounter throughout their life cycle in biological, biomedical, and environmental exposures. Given their extremely large specific surface areas and high surface reactivities, nanoparticle surfaces are dynamic and rarely (if ever) the pure nanomaterial. Instead, such surfaces comprise complex mixtures of poorly characterized and controlled adsorbates, depending on the nanomaterial exposure history. Many adsorbates bring their own biological and toxicological activities. Significantly, surface adsorption may alter otherwise benign or innocuous adsorbates to render certain antigenic or inflammatory responses on a nanomaterial surface. To understand if such a scenario truly exists and the possible risks involved, rigorous nanomaterial surface assessments combined with careful immune system activation studies are necessary. However, the appropriate analytical tools to readily ascertain such interactions and mechanisms remain lacking.