Biological interactions of oxide nanoparticles: The good and the evil

Abstract

Metal oxide nanostructures can be broadly grouped into two categories, namely industrial and medicinal nanoparticles. Industrially engineered metal oxides are heavily used in various fi elds ranging from chemical industries, the automobile sector, environmental remediation, and food and cosmetic industries. The medicinal use of metal oxide nanoparticles is in rapid expansion and deals with highly reactive oxides (e.g., TiO 2 , FeO 2 , CeO 2 ) that deeply interfere with the metabolic network of cells and organisms. In addition to the nanoscale, which provides peculiar features to materials, nano-oxides develop interactions with the complex chemistry of living matter due to their surface reactivity, which is enhanced by their extremely high surface area to volume ratio. Moreover, their ability to shed ions that can alter the surrounding bioenvironment makes them especially reactive. Such reactivity on the one hand is a biohazard, but on the other, if correctly managed, can be turned into invaluable pharmaceutical tools.Oxide nanoparticles used for medicinal studies have, in general, well-defi ned surface chemistry due to the co-synthetic or post-synthetic conjugation of linker molecules-generally of organic nature-that prevents/modulates the release of metal ions in cellular environments and imparts colloidal stability, a parameter of paramount importance when nanoparticles travel within living organisms. In addition, surface functionalization with bifunctional linkers allows selective conjugation with biomolecules, and this imparts tailored properties, such as control of delivery and cellular uptake.