Biological interactions of oxide nanoparticles: The good and the evil
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Nano-oxides and the biological world Metal oxide nanostructures can be broadly grouped into two categories, namely industrial and medicinal nanoparticles. Industrially engineered metal oxides are heavily used in various fields 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., TiO2, FeO2, CeO2) 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-defined 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.1 Great emphasis has been placed recently on the spontaneous adsorption of proteins and lipids to nano-oxide surfaces during their passage through biological fluids and tissues, forming the so-called protein or lipid corona. The binding of different proteins or lipids, which may depend, in part, on the chemical reactivity of the nanoparticle surface, theoretically could change the nanoparticle/organism interface and consequently the behavior of the nanoparticle.2 In practice, the formation of a protein corona can be viewed as an example of spontaneous functionalization, based on weak, reversible molecular interactions that buffer the nanoparticles’ surface charge, ameliorating colloidal stability and reducing ion release. The weak interactions may cause a continuous bindingand-detaching cycle with different proteins “dressing” the nanoparticle surface, conferring an ever-changing interface with the biological environment. In general, the kinetics of interaction of nanoparticles with organisms consists of crossing of the epithelia (skin, lungs, intestine) via occasional discontinuities or active passage, which is favored by the nanoparticle’s small size; once
Lina Ghibelli, Dipartimento di Biologia, Università di Roma Tor Vergata, via della Ricerca Scientifica, Roma, Italy; [email protected] Sanjay Mathur, Institute of Inorganic Chemistry, University of Cologne, Germany; sanjay.mathur@uni-ko
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