The solution
Initial investigations at the Thai synchrotron were conducted using micro X‑ray fluorecence, on skin treated with the sunscreen. The results found that Zn and Ti had accumulated within the epidermis layer but not the deeper layers of the dermis. However, the team needed to determine how deep the nanoparticles had accumulated and in which epidermal layers. In order to do this, a very small beam was needed.
Using a combination of XRF and XANES on I18 at Diamond, the SLRI scientists studied the chemical speciation of Zn present at different skin depths and mapped the elemental distribution. Thanks to the microfocus beam on I18 they could look in detail at the epidermis layer (deep inside the skin). Using porcine samples (a proxy for human skin) treated with PAN’s commercial sunscreen (Minus), they captured data at intervals of 2, 6, and 12 hours after application to measure the zinc distribution in the skin.
The results showed that TiO2 and ZnO nanoparticles used in the Minus sunscreen penetrated the skin and accumulated in the stratum corneum, stratum lucidum and upper stratum granulosum of the epidermis layer at ppm scale but not the deeper epidermis layer or dermis layer. The scientists also learned that the speciation of Zn found in the hair follicles and tissue was different from that found distributed in the stratum corneum and the sunscreen.
Findings from this study are expected to have a significant influence on the future application of topical nanoparticulate‑based technology strategies, in terms of dose and dermal distribution. The work demonstrates that synchrotron‑XRF and XANES techniques provide a useful approach for analysing commercial products using nanomaterials.
