A combination of simulation and experiment has been used to determine the charge density and structure of the surface layer that covers gold nanoparticles (AuNPs). Specifically, all-atom molecular dynamics simulations of citrate on 4, 6, and 8 nm AuNP surfaces were used to obtain the distribution of configurations and maximum packing density on citrate-coated AuNPs (cit-AuNPs) as a function of citrate charge state. A major finding of this work is that the intensive properties of the outer layer—e.g. the density and relative structuring of citrate3- and H2citrate-—are independent of the AuNP diameter. In situ Fourier-transform infrared spectroscopy experiments indicate the presence of H2citrate- within polycation-wrapped cit-AuNPs with coordination between the H2citrate- layer and polycation layer in agreement with simulations. We have thereby obtained a benchmarked all-atom H2citrate- model appropriate for molecular dynamics simulations and a justification for fixed surface-charge models appropriate for coarse-grained simulations, particularly at charged interfaces.

Surface charge density and structure for coated gold nanoparticle models

2019 Fall National Meeting

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