PEGylation of Silver Nanoparticles by Physisorption of Cyclic Poly(Ethylene Glycol) for Enhanced Dispersion Stability, Antimicrobial Activity, and Cytotoxicity

Silver nanoparticles (AgNPs) are practically valuable in biological applications. However, no steady PEGylation has been established, which is essential for internal use in humans or animals. In this study, cyclic PEG (c-PEG) without any chemical inhomogeneity is physiosorbed onto AgNPs to successfully PEGylate and drastically enhance the dispersion stability against a physiological condition, white light, and high temperature. In contrast, linear HO–PEG–OH and MeO–PEG–OMe do not confer stability to AgNPs, and HS–PEG–OMe, which is often used for gold nanoparticles, sulfidates the surface to considerably degrade the properties. TEM shows an essentially intact nanostructure of c-PEG-physiosorbed AgNPs even after heating at 95 °C, while complete disturbance is observed for other AgNPs. Molecular weight- and concentration-dependent stabilization by c-PEG is investigated, and DLS and ζ-potential measurements prove formation of a c-PEG layer on the surface of AgNPs. Furthermore, c-PEG-physiosorbed AgNPs exhibit persistent antimicrobial activity and cytotoxicity.