Date of Award

Spring 2020

Document Type

Thesis

Terms of Use

© 2020 Daniel J. Boehmler. All rights reserved. This work is freely available courtesy of the author. It may only be used for non-commercial, educational, and research purposes. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts

Department

Chemistry & Biochemistry Department

First Advisor

Kathryn R. Riley

Abstract

Engineered nanomaterials (ENMs) have become increasingly popular for use in both industrial and consumer settings in recent years. Of the myriad of materials used to synthesize ENMs, silver is one of the most common. Silver nanoparticles (AgNPs) undergo dynamic transformations in biological environments, leading to modifications in their reactivity, surface interactions, and speciation. In particular, release of ionic silver (Ag(I)(aq)) through AgNP dissolution can have significant impacts on ecological and human health. Thus, quantifying AgNP dissolution rates in biologically relevant matrices can provide valuable information regarding their potential cytotoxic effects. Linear sweep stripping voltammetry (LSSV) is a technique that provides high throughput, in situ measurements of the concentration of Ag(I)(aq) dissolved from AgNPs. These measurements are better time-resolved and have comparable sensitivities to those obtained using atomic spectroscopic techniques, allowing for more detailed investigation of AgNP dissolution kinetics. LSSV was first used to investigate the dissolution of AgNPs in the presence of bovine serum albumin (BSA), a point-of-use system used to model medical and consumer applications of AgNPs. Dissolution of AgNPs was enhanced in the presence of BSA in a concentration-dependent manner. This effect was also dependent on AgNP diameter, with smaller particles exhibiting a greater degree of BSA-enhanced dissolution than larger particles. These findings were supported by AgNP-BSA binding assays, which showed a subtle decrease in AgNP-BSA binding strength with decreasing AgNP size. These data point to a model in which Ag(I)(aq)-loaded BSA is displaced by BSA in the bulk solution in a more facile manner at the surface of smaller AgNPs. LSSV was subsequently used to probe the dissolution of AgNPs in the presence of peptone yeast extract growth medium (PYE) and metabolites isolated from the bacterium Caulobacter crescentus, referred to as "spent medium". There is significant overlap between common AgNP waste repositories and the habitats of C. crescentus, making this a relevant end-of-use model. Dissolution of AgNPs was mediated by spent medium in a culture density-dependent manner. DLS size data show increasing hydrodynamic diameter of AgNPs when incubated with spent medium from increasingly dense cultures, supporting these findings. We hypothesize that glutathione (GSH) levels in spent medium vary with the density of their derivative culture, and that GSH is responsible for both this dissolution trend and surface layer formation on AgNPs. Both the point-of-use and end-of-use models investigated here allowed us to characterize AgNP dissolution in a wide range of environments. Further, the novel application of LSSV to study AgNP dissolution kinetics can be expanded to encompass other model proteins and bacterial species. In this way, the present work both advances our understanding of complex AgNP transformations and provides quantitative analytical tools that can be easily accessed and more broadly applied by other researchers in the nanotechnology field.

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