Porous media-induced aggregation of protein-stabilized gold nanoparticles

Gold-nanoparticles (AuNPs) are employed for cancer treatment, drug delivery, chemical analyses, and many other uses. As AuNP manufacture increases, it is imperative that we understand the environmental fate of these nanomaterials. We investigated the transport and stability of AuNPs under simulated groundwater conditions. Batch experiments indicated that 16 nm AuNPs stabilized with bovine serum albumin (BSA-cit-AuNPs) was slightly more stable under high ionic strength conditions than citrate-functionalized AuNPs (cit-AuNPs) of the same core size. Both types of AuNPs were injected into glass bead-packed columns and subjected to transport with varying NaCl and CaCl2 concentrations. BSA-cit-AuNPs deposited less than cit-AuNPs in the presence of increasing concentrations of CaCl2, but the opposite trend was observed in the presence of increasing concentrations of NaCl. This finding differed from the results obtained in the batch studies. Calculated attachment efficiencies (α) failed to reflect the observed experimental column data, with α at maximum only approaching 0.1 even though a majority of the AuNPs were retained in the column. Colloid filtration theory fails to predict and explain this discrepancy. We conclude that media induced nanoparticle aggregation is responsible for the inconsistency.