The Effect of zeta-Potential and Hydrodynamic Size on Nanoparticle Interactions in Hydrogels

Abstract

The zeta-potential and hydrodynamic size (d(h)) of nanoparticles (NPs) are systematically controlled by capping gold NPs (AuNPs) with polymers having different charges and treating them in NaCl solutions of diverse concentrations. Interactions between AuNPs in hydrogel are caused by chemical reactions induced by 1,4-dithiothreitol. The effect of zeta-potential is clear, as negatively charged AuNPs can be aggregated in neutral agarose gel, but the amount of aggregation is significantly affected by the magnitude of the negative surface charge on the AuNPs. However, all positively charged AuNPs show negligible aggregation in agarose gel with slightly negative polarity. The effect of d(h) on AuNP aggregation is different from that of zeta-potential. Although AuNPs with small d(h) generally show more aggregation than those with large d(h), the amount of AuNP capping layer is critical. Thus, the amount of polymer present on NP surface needs to be considered to investigate the effect of d(h) on AuNP aggregation. Through extended Derjaguin, Landau, Verwey, Overbeek (XDLVO) theory, it is shown that the charges of the AuNPs and the hydrogel, as well as the d(h) of the NPs, are related to electrostatic repulsion and steric hindrance, which affect AuNP aggregation in hydrogel.