Serum proteins prevent aggregation of Fe2O3 and ZnO nanoparticles

Abstract

Aggregation of metal oxide nanoparticles in aqueous media complicates interpretation of in vitro studies of nanoparticle-cell interactions. We used dynamic light scattering to investigate the aggregation dynamics of iron oxide and zinc oxide nanoparticles. Our results show that iron oxide particles aggregate more readily than zinc oxide particles. Pretreatment with serum stabilises iron oxide and zinc oxide nanoparticles against aggregation. Serum-treated iron oxide is stable only in pure water, while zinc oxide is stable in water or cell culture media. These findings, combined with zeta potential measurements and quantification of proteins adsorbed on particle surface, suggest that serum stabilisation of iron oxide particles occurs primarily through protein adsorption and resulting net surface charge. Zinc oxide stabilisation, however, also involves steric hindrance of particle aggregation. Fluid shear at levels used in flow experiments breaks up iron oxide particle aggregates. These results enhance our understanding of nanoparticle aggregation and its consequences for research on the biological effects of nanomaterials.

Figure 1

Validation of the count rate method. Count rate variation with particle concentration to the power of 0.91 correlates extremely well with the data (r² > 0.999).

Figure 2

TEM images of iron oxide (right) and zinc oxide (left) nanoparticle aggregates.

Figure 3

Dispersion and recovery of metal oxide nanoparticles. Each measure was calculated independently for each of six trials and then averaged. Data are mean ± SEM. (A) Iron oxide (10 μg/ml). (B) Zinc oxide (50 μg/ml).

Figure 4

Short-term aging of iron oxide nanoparticles. (A) Particle size. (B) Scattering intensity. Measured values from three replicates were averaged at each 1-h time step. Data are mean ± SEM.

Figure 5

Short-term aging of zinc oxide nanoparticles. (A) Particle size. (B) Scattering intensity. Measured values from three replicates were averaged at each 1-h time step. Data are mean ± SEM.

Figure 6

Effect of serum on zeta potential in various diluents for iron oxide and zinc oxide nanoparticles. Each data point is the average of three experiments. Data are mean ± SEM.

Figure 7

Effect of flow on aggregation of iron oxide nanoparticles in complete medium. (A) Evolution of particle diameter over 4 h under static conditions. Also shown is particle diameter under flow conditions at the end of the 4-h period. Data are mean ± SEM with n = 4. (B) Evolution of particle diameter over 4 h under flow conditions. Also shown are particle diameters under static conditions at the beginning and end of the 4-h period. Data are mean ± SEM with n = 2.

Figure 8

Concentration of protein, normalised by specific surface area, adsorbed on iron oxide and zinc oxide nanoparticles in DI water and PBS diluents. Data are mean ± SEM with n = 3.