(605i) Electric Potential of Citrate Capped Gold Nanoparticles: Effects of Salt Concentration and Poly(Allylamine Hydrochloride) Wrapping

Polyelectrolyte-coated gold nanoparticles (AuNPs) are important to biomedical applications. In this paper, we use all-atom molecular dynamics (MD) simulations to study the electric potential around the citrate capped gold nanoparticle (cit-AuNP) and poly(allylamine hydrochloride) (PAH) wrapped cit-AuNP (PAH- AuNP). We focus on discuss the ionic strength and PAH wrapping effects on the electric potential. The ion radial distributions for both cit-AuNP and PAH-AuNP are calculated from MD simulations in different salt concentrations (0 M, 0.001 M, 0.005 M, 0.01 M, 0.05 M, 0.1 M and 0.2 M NaCl). The net charge distribution (Z(r)) around the nanoparticle is obtained from the ion distribution, which is further used to calculate the electric potential (φ(r)). The hydrodynic radius (RH) is chosen from literatures. In 0.001 M NaCl, our MD simulation result shows that the cit-AuNP ζ = −25.5 mV at RH = 85 Å, and after wrapping with one PAH, the PAH-AuNP reduces to ζ = −8.6 mV at RH = 89.5 Å. We find that after PAH wrapping the nanoparticle surface charge is reduced, the ion distribution is changed, and the magnitude of ζ-potential reduces significantly. In the end, we also compare our MD simulation φ(r) results with the classic Poisson- Boltzmann Equation (PBE) approximation and the well-known Derjaguin-Landau-Verwey-Overbeek (DLVO) theory results.