Enhanced Stability of Anisotropic Gold Nanoparticles by Poly(N-isopropylacrylamide)

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.

Shape dependent protein-induced stabilization of gold nanoparticles:From a protein corona perspective Special Collection:Distinguished Australian Researchers

Gold nanoparticles(AuNPs)are promising materials for many bioapplications.However,upon contacting with biological media,AuNPs undergo changes.The interaction with proteins results in the so-called protein corona(PC)around AuNPs,leading to the new bioidentity and optical properties.Understanding the mechanisms of PC formation and its functions can help us to utilise its benefits and avoid its drawbacks.To date,most of the previous works aimed to understand the mechanisms governing PC formation and focused on the spherical nanoparticles,although non-spherical nanoparticles are designed for a wide range of applications in biosensing.In this work,we investigated the differences in PC formation on spherical and anisotropic AuNPs(nanostars in particular)from the joint experimental(extinction spectroscopy,zeta potential and surface-enhanced Raman scattering[SERS])and computational methods(the finite element method and molecular dynamics[MD]simulations).We discovered that protein does not fully cover the surface of anisotropic nanoparticles,leaving SERS hot-spots at the tips and high curvature edges‘available’for analyte binding(no SERS signal after pre-incubation with protein)while providing protein-induced stabilization(indicated by extinction spectroscopy)of the AuNPs by providing a protein layer around the particle’s core.The findings are confirmed from our MD simulations,the adsorption energy significantly decreases with the increased radius of curvature,so that tips(adsorption energy:2762.334 kJ/mol)would be the least preferential binding site compared to core(adsorption energy:11819.263 kJ/mol).These observations will help the development of new nanostructures with improved sensing and targeting ability.