Dynamics of silver nanoparticles in human skin in vivo studied by synchrotron radiation and ICP-MS

The topical application of silver nanoparticles (AgNPs) is increasingly used in the treatment of burns to prevent infections and favour the regeneration of the tissue. We have shown that AgNPs can penetrate into the dermis, are taken up by the fibroblasts and interact with mitochondria,1-3 but no data are currently available on their subsequent chemical transformations, which are key processes to determine their potential toxicity. Here, we present the first high resolution spatial and temporal data on silver distribution and speciation in depth profiles of burned skin after application of AgNPs. Full-profile biopsies of the wound were collected from a patient before treatment, and then at 3-days intervals up to the complete healing. Elemental imaging maps and speciation were obtained using synchrotron radiation μXRF and μXANES on selected slices from each biopsy, and allowed to elucidate the chemical transformations and penetration of AgNPs into the tissue. The potential of AgNPs to reach the systemic circulation was investigated by developing a new analytical method for the simultaneous determination of dissolved Ag and characterization of AgNPs in human blood, based on hydrodynamic chromatography hyphenated to single-particle ICP-MS, and combined with a new ad-hoc algorithm for data treatment. Within a single analytical run, the method provides the deconvoluted chromatogram and concentration of dissolved Ag species, and the multidimensional distribution of AgNPs in terms of hydrodynamic diameter, mass-derived diameter, size-dependent number and mass concentrations, total number and mass concentration. The method was applied to study the dynamics of AgNPs in human plasma in vitro, and to investigate the presence of AgNPs in the blood of three burnt patients.