Acetylation of dendrimer-entrapped gold and silver nanoparticles

Surface functionalization of dendrimer-entrapped metal nanoparticles (NPs) is of great importance in the area of biological sensing and therapeutics. In this work, dendrimer-entrapped gold and silver NPs (Au DENPs and Ag DENPs) prepared using amine-terminated poly(amidoamine) dendrimers of generation 5 (G5.NH2) as templates were subjected to acetylation in order to neutralize the surface positive charges. UV-Vis spectrometry, nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), polyacrylamide gel electrophoresis (PAGE), and zeta-potential measurements were utilized to characterize both Au DENPs and Ag DENPs modified with a defined degree of acetylation. The size, size distribution, optical properties, water solubility, and stability of Au DENPs do not change after acetylation, while their surface charges change. In contrast, acetylated Ag DENPs show optical properties that are slightly different from the unmodified ones, while reserving similar water solubility and stability. The surface charge decreases towards neutral with an increasing degree of acetylation. More interestingly, the size of partially acetylated Ag DENPs displays a bimodal distribution (2.9 nm and 11.0 nm), whereas the pristine Ag DENPs and the completely acetylated Ag DENPs are relatively monodisperse with sizes of 2.9 nm and 11.0 nm, respectively. It indicates that complete acetylation transfers Ag DENPs to dendrimer-stabilized Ag NPs (Ag DSNPs). The size and morphology changes of Au and Ag DENPs upon acetylation were further confirmed by molecular dynamics simulations. Such synthetic modifications are expected to reduce the toxicity of dendrimer-entrapped metal NPs and offer further biofunctionalization to produce multifunctional metal NPs for a range of biological sensing and therapeutics applications.