CREATING AND CHARACTERIZING NANOPARTICLE AGGLOMERATES TO STUDY EFFECT OF AGGLOMERATION AND POLYMER COATING ON DISSOLUTION, ABSORBANCE SPECTRUM, AND TOXICITY

Justin M. Zook, Robert I. MacCuspie, Vinayak Rastogi, Danielle Cleveland, Stephen Long, Laurie Locascio, John Elliott.

Nanoparticles (NPs) frequently agglomerate in biological or environmental media, but very few methods exist to prepare and characterize agglomerates with different stable size distributions in these media.  We have developed methods to prepare stable agglomerates of different sizes of various types of NPs in cell culture media and environmental media using protein or natural organic matter, respectively, to stabilize the agglomerates.  These agglomerates have applications in NP toxicity studies, localized surface plasmon resonance (lSPR)-based biosensors, and surface enhanced Raman spectroscopy sensors.

We used analytical ultracentrifugation (AUC) to separate the NP agglomerates by size and thereby characterize their size distribution.  We compared the AUC size distributions to those predicted by dynamic light scattering measurements and aggregation theory, and found that actual size distributions are often broader than expected.  In addition, we use AUC to measure how the lSPR absorbance spectrum depends on agglomerate size, since traditional methods only measure the bulk absorbance of a range of sizes.  We then show how this new information can be used to calculate the size distribution of small agglomerates simply from their bulk absorbance spectrum.

Finally, we study the effect of silver NP polymer coatings and agglomeration on silver ion dissolution and toxicity.  We validate a new absorbance-based method for measuring silver ion dissolution in complex matrices. We find that both polymer coatings and agglomeration can decrease the dissolution rate. We also show that this dissolution rate is correlated with their toxicity to red blood cells, so that polymer coatings and agglomeration probably affect the hemolytic toxicity of silver NPs primarily by decreasing the dissolution rate.