Synchrotron-based X-ray fluorescence study of gold nanorods and skin elements distribution into excised human skin layers.

Understanding the distribution of nanoparticles in skin layers is fundamentally important and essential for developing nanoparticle-based dermal drug delivery systems. In the present study, we provide insights into the distribution of gold nanorods (GNRs) functionalized with hydrophobic or hydrophilic ligands in human skin layers using synchrotron X-ray fluorescence (SR-XRF) spectroscopy, confocal microscopy, and transmission electron microscopy. The results confirmed the important role that the surface chemistry of GNRs plays in their penetration into the skin; the GNRs coated with polyethylene glycol were distributed into the skin layers to a greater extent than the GNRs coated with hydrophobic polystyrene thiol. In addition, SR-XRF analysis revealed that the spatial distribution of endogenous elements (phosphorus and sulfur) in skin layers demonstrated a significant "anti-correlation" relationship with that of GNRs. These results suggest possible association (via adsorption) between the GNRs and these two elements localized in skin, which can be valuable for understanding the penetration mechanism of gold nanoparticles into the skin.