Quantitative Analysis of Silica, Gold, and Silver

ICP-OES was performed on PerkinElmer Optima 8000 to quantify the elemental distribution of silica (Si), gold (Au), and silver (Ag). Si, Au, and Ag standards (0, 0.2, 2, 4, and 10 ppm) were prepared from commercially available 1000 ppm Si, Au, and Ag(ii) standard solutions and dissolved in 5% Aqua Regia. SiO₂NP, SiO₂AuNP, and PhaNPs (200 μl) samples were dissolved overnight in 500 μl of 100% Aqua Regia (3 : 1 hydrochloric acid : nitric acid), followed by the addition of 9.5 ml DI water to a final concentration of 5% Aqua Regia. Si, Au, and Ag emission spectra were collected at 251.611 nm, 267.595 nm, and 328.068 nm, respectively. Emission spectra for yttrium (Y), an internal standard, were collected at 371.029 nm.