Quantitative measurement of sodium polystyrene sulfonate adsorption onto CTAB capped gold nanoparticles reveals hard and soft coronas.

ABSTRACT

Accumulated evidence indicates that nanoparticle behavior in complex biological environments strongly depends on the nanoparticles' surface chemistry. A common way to modify nanoparticles is to deposit oppositely charged molecules on the surfaces in a Layer-by-Layer fashion to build up thin films of polymers. While this polymer coating is a well-developed technique, the quantification of polymers deposited and physical mechanism of polymer deposition remain relatively unstudied. In this work CTAB capped gold nanoparticles, synthesized in a flow reactor, are coated with sodium polystyrene sulfonate and purified through a series of equilibrium dialysis steps. Throughout the process, zeta potential, UV-Vis spectroscopy, DLS, and TEM are used to monitor the physiochemical properties of the nanoparticless while ICP-OES is used to quantify polyelectrolyte deposition. Through these measurements, we find that traditional purification techniques result in particles that likely consist of both a tightly bound hard corona and a loosely-bound soft corona of polymers. Finally, we quantify the relative numbers of polymers in each corona which are approximately 100 and 1000 polymer molecules per nanoparticle for the hard and soft coronas, respectively, and use these to propose a binding model for the hard corona.