Evaluating Nanoparticle Permeation in Human Skin via μ-PIXE

This study investigates the diffusion and spatial distribution of gold nanoparticles (AuNPs) through skin using microbeam Particle-Induced X-ray Emission (μ-PIXE). Spherical AuNPs with an average diameter of 4-5 nm were chemically synthesized and applied in permeation experiments with human skin. The results demonstrated that the stratum corneum and epidermis constitute highly effective barriers to AuNP permeation, with gold concentrations predominantly localized in the outermost layers (∼699 ppm in the stratum corneum and ∼181 ppm in the epidermis), while negligible amounts reached deeper skin regions. The diffusion coefficient of AuNPs in the human stratum corneum was estimated as 3 × 10⁻⁷ cm²/h. Overall, this study demonstrates that μ-PIXE is a powerful and reliable technique for quantitatively assessing trace-level metallic nanoparticle permeation with spatial resolution, providing critical insights for transdermal drug delivery research, biosafety evaluation, and the emerging application of nanoparticle-assisted radiosensitization.