Gold and silver quantification from gold-silver nanoshells in HaCaT cells

A method to determine total gold (Au) and/or silver (Ag) elemental concentrations from gold nanoparticles, Au-Ag nanoshells (NS) and silica coated Au-Ag nanoshells was developed, evaluated and validated. Samples were mineralized in a mixture of concentrated aqua regia and hydrofluoric acid at 65 °C for 4 h. Mineralized solutions were diluted and standard solutions were prepared in aqua regia 5%. ICP-MS analysis was performed with or without the use of a reaction cell (CRC). For the determination of elemental concentrations of nanopowders and test suspensions, the average recovery was 99 ± 2% and 101 ± 2% for gold and silver respectively. The repeatability was evaluated by the Relative Standard Deviation (RSD). The overall analytical RSD was ≤4% (n = 3) and the RSD associated to ICP-MS analysis was ≤2% (n = 10). The limits of detection were 0.005 and 0.002 μg(element) L^-1 (analyzed solution), and the limits of quantitation 0.017 and 0.005 μg(element) L^-1 (analyzed solution), for ¹⁹⁷Au and ¹⁰⁹Ag respectively. The Ag/Au mass ratios of the NS in the different samples considered were all equal to (0.93 ± 0.04). From this information, the average thickness of gold and silver layers in the nanoshells was deduced, being 7.5 ± 0.5 and 23 ± 3 nm respectively. Finally, the developed method was successfully applied to in vitro studies to evaluate NS cellular uptake in HaCaT keratinocyte cells confirming the method robustness toward biological medium. Experiments in cell culture medium gave coherent concentrations, 70-100% of uncoated or silica-coated NS being recovered, distributed between the culture medium and the cells (internalized). The analytical repeatability (over the whole procedure, or that of the ICP-MS analysis only) remains in the same order of magnitude as in test suspensions. Minimum concentrations less than or equal to 1 μg(element) g^-1(suspension) were determined with the same accuracy.