Controlling Nanoparticle Adsorption to Weak Polyelectrolyte Layer-by-Layer Films*

Designing materials to control adsorption of nano-sized objects is essential in many applications including the separation and purification of proteins, nanoparticle (NP) synthesis, and water filtration. Essential to this task is an understanding of the underlying interactions that influence nanoparticle transport and adsorption. Using a model layer-by-layer (LbL) system of alternating poly(allyl amine hydrochloride) (PAH) and poly(acrylic acid) (PAA), we study the adsorption of 20 nm poly(ethylene glycol)-carboxylic acid functionalized gold NPs (Au-PEG_12-COOH NPs) to 50 nm LbL films on a silicon or glass substrates. By complimenting macroscopic quartz crystal microbalance with dissipation (QCM-D) with microscopic in situ, label-free interferometric scattering microscopy (iSCAT) and scanning electron microscopy (SEM) measurements, we demonstrate the ability to control adsorption by modifying the capping layer chemistry (PAA vs. PAH), adsorption experiment solution pH, and thermal crosslinking temperature of the LbL films prior to particle exposure and quantify effects of these variables on surface coverage, interaction mechanism, and kinetics of adsorption.