Anisotropic surface functionalization of Au nanorods driven by molecular architecture and curvature effects

GONZALEZ SOLVEYRA, ESTEFANIA; TAGLIAZUCCHI, MARIO; SZLEIFER, IGAL

Glasgow

Simposio; Faraday Discussion: Nanoparticles with Morphological and Functional Anisotropy; 2016

Royal Society of Chemistry

In this work we seek to identify the design rules for obtaining gold nanorods (Au-NRs) that combine surface-adsorbed polymers of different molecular architecture (intramolecular connectivity of monomers) and functionality in a spatially resolved manner. This kind of anisotropic nanoconstruct offers interesting properties for biomedical applications involving transport, delivery, and cellular uptake.The questions we are asking is whether it is possible to spatially control the functionalization of nanosystems combining curvature and molecular architecture effects, and more specifically, if it is possible to outline rules using molecular modelling to direct and assist the design and experimental synthesis of functionalized Au-NRs. To answer such questions, we modelled the end-polymer adsorption process from aqueous solutions containing one or two polymers onto surfaces of different morphology (cylinders and spheres, representing the NR?s body and tip respectively) and curvature (radius). Our theoretical approach explicitly considered the geometry of the system, the shape, molecular volume and conformations of all molecular species, and the interactions among them (excluded volume and van der Waals). We performed a systematic analysis on the adsorption process varying backbone length, number of branches, branching positions, and total number of monomers of the polymer molecules. We conducted calculations on over 100 different polymer mixtures in 50 aqueous solutions of different compositions. The adsorption process is governed by the balance between repulsion forces, polymer-surface and polymer-polymer attractions at the surface, and is in turn modulated by its morphology and curvature. Polymer adsorption changes dramatically when introducing a second polymer to the bulk solution and, moreover, becomes polymer-mixture specific. The ability of a polymer to stretch will drive its partition towards regions of greater curvature (NR tips vs. body), given the greater available volume moving away from the surface. Interestingly, the surface composition at spheres or cylinders of the same radius differs from each other, and in turn departs from that of the solution composition. Surface density of polymers and spatial partitioning can be tuned by changing the polymer mixture pair and the size of the NP. Our results suggest that combining molecular architecture and curvature at the nanoscale could render anisotropic nanoparticles with spatial enriched domains. Selective functionalization of such domains could allow obtaining nanoconstructs with different and directional functionalities.