Chemical composition of surface-functionalized gold nanoparticles

The composition of surface-functionalized gold nanoparticles (diameter of the metallic core: 17–20 nm) was determined by elemental analysis (C, H, N, S, Au, Na) after preparation of a larger batch. Gold nanoparticles were prepared and functionalized with citrate according to the classical Turkevich method. The citrate-functionalized nanoparticles contained about 3.1 wt% of organic material (135 ng cm⁻² or 3.1 molecules nm⁻²). A partial exchange of citrate was accomplished by tris(sodium-m-sulfonato-phenyl)phosphine (TPPTS) which led to 2.1 wt% of citrate (90 ng cm⁻² or 2.1 molecules nm⁻²) and 1.4 wt% TPPTS (61 ng cm⁻² or 0.6 molecules nm⁻²). The citrate coating was quantitatively exchanged by poly(N-vinyl pyrrolidone) (PVP) after immersion in solutions with concentrations of 33, 66 and 128 mg L^-1, respectively, leading to contents of 4 to 6 wt% of PVP (171–271 ng cm⁻² or 9–15 PVP monomer units nm⁻²).