05.27.08
Nanoparticles, UVA Protection and Testing
The nanoparticle controversy brings up the all-important question of testing. What do we know, what tests are presently available, and what is on the horizon? I talked to Dr. Jay L. Nadeau, professor of bio-medical engineering at McGill University, who heads a nanotechnology research group funded under EPA’s STAR (Science and Technology to Achieve Results) program. One of the results of their research has been the publication of a quantitative test of free-radical generation from nanoparticles in solution.
I described to her the difficulties associated with testing levels of UVA protection in sunscreen. Testing protection against longer UV wavelengths (from 330 to 400+ nanomaters) is not as intuitive as UVB testing, which simply tests for protection against the immediately visible effects of burning. UVA rays don’t burn you, they age you, so it makes sense that these longer-term effects would be harder to measure. However, one test that has been adopted by Japan and Europe, called Persistent Pigment Darkening, (PPD), uses essentially the same methodology as is used in SPF testing. L’Oreal Research presented such a PPD test model in their recent study.
In the L’Oreal study human volunteers were exposed to 330-440 nm of light 3 times a week for 4 weeks. Exposed sites were compared with nonexposed sites, exposed sites protected with a broad UVA absorber, and exposed sites to which a sunscreen vehicle had been applied. Various parameters related to early photoaging due to UVA exposure, including pigment darkening, stratum corneum thickening and changes in elasticity, were measured.
This is a clumsy testing method to say the least, especially as it requires the use of human volunteers who must be subjected to potentially harmful UV rays. Dr. Nadeau suggests that “absorbance spectroscopy and fluorescence-based assays can also quantify UVA absorption.” (see “Photosynthesis of dopamine-modified quantum dots and effects on biological systems,” Clarke, Hollmann, Zhang, Suffern, Bradforth, Dmitrijevic, Minarik and Nadeau, Nature Materials 5(5): 409-17 (2006).
In other words, nanoparticles may be instrumental in resolving issues around nanoparticle safety, which certainly makes for an elegant solution. I am very hopeful that we will soon be seeing less invasive and more reliable testing coming from the nanotechnology community.
