Anti-pollution in skin and hair care is appearing on everyone's wish list, although according to recent authors in the Royal Society of Chemistry's Advances, formulating nanoparticle-based cosmetics to protect skin against environmental stress is a challenging task. As such, they sought to develop an emulsion with potent free radical-scavenging activity.
According to the article abstract, bluish-tinted, nano-sized cerium oxide (CeO2) nanoparticles, i.e., nanoceria, were prepared by thermal decomposition and encapsulated by amine-containing polyethylenimine. The particles were characterized instrumentally as nearly spherical, monodispersed and 3−10 nm in size, among other factors.
In vitro antioxidant assays showed the pigmented nanoceria were effective against nitrile and peroxy radicals. In the future, the researchers will evaluate the pigmented nanoceria-containing emulsion as potential medicinal cosmetic to protect skin.
Although these findings alone are enough to get skin care formulators excited, I couldn't help but wonder: Why blue? Was this an intentional change to the material or an innate characteristic? The abstract never stated; you can login to read the full report if you have access. If you know the answer, I'd love to hear it. Email firstname.lastname@example.org. In the meantime, I'm reaching out to the authors.
Perhaps previous work from Shailendra Girithe, of the Mayo Clinic, et al., can explain. Girithe and co-authors described in 2013 how nanotechnology-based tools are rapidly emerging for medical imaging and targeted drug delivery. In particular, cerium oxide, a rare-earth oxide, gained interest for fighting ovarian cancer. In its nanocrystalline form, cerium oxide (nanoceria, or NCe) exhibits a blue shift in the ultraviolet absorption spectrum. According to the authors, this shifting and broadening of Raman allowed modes and lattice expansion, as compared to bulk cerium oxide, indicating nanoceria has unique properties.
So the bluish tint appears to be an innate property of this interesting material. Girithe et al went on to explain that NCe has a unique ability to switch oxidation states between (III) and (IV) depending upon the environment, which is a property comparable to biological antioxidants. Thus, nanoceria can be "tuned."
The authors note the regenerative antioxidant properties are based on the valence structure of the cerium atom along with inherent defects in the crystal lattice structure. This unique structure can promote cell longevity and decrease toxic insults by preventing the accumulation of reactive oxygen species (ROS) in the cell.
While I'm left wondering about the blue nature of this material, for formulators it seems irrelevant. The end results speak for themselves: You can tune the material to protect skin in such a way that only reactive oxygen species are left singing the blues.