Synthesis, characterization and in vitro effects of 7 nm alloyed silver-gold nanoparticles

Abstract

Alloyed silver-gold nanoparticles were prepared in nine different metal compositions with silver/gold molar ratios of ranging from 90:10 to 10:90. The one-pot synthesis in aqueous medium can easily be modified to gain control over the final particle diameter and the stabilizing agents. The purification of the particles to remove synthesis by-products (which is an important factor for subsequent in vitro experiments) was carried out by multiple ultracentrifugation steps. Characterization by transmission electron microscopy (TEM), differential centrifugal sedimentation (DCS), dynamic light scattering (DLS), UV-vis spectroscopy and atomic absorption spectroscopy (AAS) showed spherical, monodisperse, colloidally stable silver-gold nanoparticles of ≈7 nm diameter with measured molar metal compositions very close to the theoretical values. The examination of the nanoparticle cytotoxicity towards HeLa cells and human mesenchymal stem cells (hMSCs) showed that the toxicity is not proportional to the silver content. Nanoparticles with a silver/gold molar composition of 80:20 showed the highest toxicity.

Keywords: cytotoxicity; gold; nanoalloys; nanoparticles; silver.

Figure 1

Transmission electron micrographs of PVP-functionalized Ag/Au nanoparticles: (A) Ag/Au 10:90, d = 6.5 nm; (B) Ag/Au 30:70, d = 7.1 nm; (C) Ag/Au 90:10, d = 11.5 nm, with the particle size distribution shown in the histograms.

Figure 2

DCS results of Ag/Au–PVP nanoparticles of three different compositions: Ag/Au 40:60, d = 5.3 nm; Ag/Au 60:40, d = 5.5 nm; Ag/Au 10:90, d = 5.8 nm.

Figure 3

UV–vis spectra of PVP-functionalized Ag/Au nanoparticles and pure Ag and Au nanoparticles.

Figure 4

Overview of the absorption maxima in UV–vis spectroscopy of PVP-functionalized Ag/Au nanoparticles as function of the experimentally determined silver molar content (Table 2).

Figure 5

The viability of HeLa cells after incubation with alloyed nanoparticles and pure silver and gold nanoparticles according to the nominal silver content. The experiments were carried out at total metal concentrations of 5, 50, and 100 µg mL⁻¹. The cytotoxicity tests were performed at (A) 5 h, (B) 24 h, (C) and 72 h after the nanoparticle addition. The dotted lines indicate the viability of the control (untreated cells).

Figure 6

The viability of hMSCs after incubation with alloyed nanoparticles and pure silver and gold nanoparticles according to the nominal silver content. The experiments were carried out at total metal concentrations of 5 and 50 µg mL⁻¹. The cytotoxicity tests were performed at (A) 5 h, (B) 24 h, (C) and 72 h after the nanoparticle addition. The dotted lines indicate the viability of the control (untreated cells).