Single particle ICP-MS in a multitechnique approach to elucidate the fate of silver nanoparticles in burnt patients

The topical administration of silver nanoparticles (AgNPs) is increasingly used in the treatment of burns to prevent infections and favour the regeneration of the tissue. Beside the antibacterial efficacy, we have documented that AgNPs can penetrate into the dermis, be up taken by the fibroblasts and affect mitochondrial activity, but no direct observations are currently available on their subsequent chemical transformation and fate in vivo in the human body, particularly concerning their potential to reach the circulatory system. We developed a method for the simultaneous determination of dissolved Ag and the characterization of AgNPs in human plasma and blood, based on hydrodynamic chromatography hyphenated to ICP-MS in single particle detection mode, and combined with a dedicated algorithm for data treatment. From a single analysis, the method provides the concentration of dissolved Ag and the distribution of AgNPs according to the hydrodynamic diameter, mass-derived diameter, number and mass concentration. The method was applied to investigate the transformations of AgNPs standards and an AgNPs-coated dressing in human plasma, supported by synchrotron radiation μXRF imaging and μXANES speciation, showing that chlorides and protein thiols co-participate in the partial dissolution of AgNPs on an hourly time scale through dynamics driven by kinetic factors. Our methodology was then implemented within a multitechnique approach to study the transformations of AgNPs after topical administration to real burnt patients in hospital conditions. Of the 30 to 80 ng mL-1 of total Ag found in the whole blood of patients, the dissolved fraction was not statistically different from the total level of the metal, while NPs or aggregates were not detected. Combined with the Ag distribution and speciation in skin biopsies from corresponding patients, studied by laser ablation-ICP-MS, μXRF and μXANES, the work provided new and complete insights into the metallomics of AgNPs in humans and in vivo. Overall, our results support the hypothesis that the systemic mobilization of the metal after topical administration of AgNPs is mainly driven by their dissolution in situ.