Abstract:

A simple synthetic method has been described to prepare anisotropic gold nanoparticles (AuNPs) possessing unique optical and structural properties at room temperature, and subsequently the nanoparticles have been stabilized by temperature-sensitive poly(N-isopropylacrylamide), or poly(NIPAM). Although poly(NIPAM) does not exhibit a strong binding affinity to gold, simply introducing poly(NIPAM) to these unstable anisotropic AuNPs can maintain the original structures and absorption properties for several weeks. This increased stability is presumably caused by the adsorbed polymer layer around the anisotropic AuNPs. The existence of adsorbed linear poly(NIPAM) around the AuNPs is confirmed through the reversible absorption properties of the nanoparticles upon heating and cooling. To verify the presence of weak attractive forces (e.g., van der Waals, dipole–dipole, and possible hydrogen bonding) between the polymer and the AuNPs, various concentrations of linear poly(NIPAM) are introduced during the formation of the AuNPs resulting in the systematical control of the size and roughness of the nanoparticles. In addition, the preferential attachment of pre-formed anisotropic AuNPs on cross-linked poly(NIPAM) nanoparticles indicates the presence of weak attractive forces between AuNPs and poly(NIPAM). As such, poly(NIPAM) and its derivatives can serve as a useful stabilizing and capping agent to preserve the properties of the anisotropic AuNPs.