Structure and Zeta Potential of Gold Nanoparticles with Coronas of Varying Size and Composition

Abstract

The structure of the soft ligand shell in engineered nanoparticles is related to their physical and chemical properties. The variation in that structre is critical for extending the diversity of functions in a wide variety of applications. To uncover the structure of soft PAH coronas wrapped on gold nanoparticles (AuNPs), in particular, we used atomistic simulations in this work. We found that increasing the number of PAH chains can increase both the size of the soft PAH corona and the magnitude of the electric potential of the PAH-wrapped cit-AuNPs (PAH-AuNPs). We also found that when the salt concentration increases, both the soft corona size and the electric potential decrease due to Debye screening. We compared the ligand structures, ion distributions, and electric potentials of 5 different nanoparticles─viz. citrate, PAH, 3-mercapto-propionic acid (MPA), 16-mercapto-hexadecyl-trimethylammonium bromide (MTAB), and hexadecyl-trimethylammonium bromide (CTAB) capped AuNPs. We found that when the surface charge densities are similar, these 5 different nanoparticles have similar electric potential profiles, but their ligand structures differ. Using Debye-Hückel theory, we determine the slipping planes (at the hydrodynamic radius, RH) and calculate the ζ-potentials of different AuNPs. We compared several machine learning (ML) models to predict the ζ-potential values learned from our simulation data and found that the Extra Trees model is the best at rationalizing the experimental data.