The Impact of Nanomaterial Functionalization and Core Chemical Composition on Toxicity to Daphnia Magna

Nanomaterials (NMs) are being developed for a variety of industrial, biomedical, and environmental applications. Initially these materials consisted of simple metal oxides or carbon based NMs. More recently NMs have become increasingly complex consisting of multiple transition metals and surfaces functionalized with polymers, surfactants and ligands that have the ability to alter their physiochemical properties and enhance performance. As manufactured NM production increases, so does the concern about their release into the environment and potentially harmful effects. The focus of toxicology has largely been on first generation materials and we have comparatively less information about the potential impacts of complex NMs. In order to create environmentally friendly nanotechnologies, the properties that govern NM toxicity need to be better elucidated. In addition, understanding mechanisms for toxicity and impacts to molecular and apical endpoints will greatly aid in the rapid assessment and design of current and future nanotechnologies. In this dissertation my central hypothesis is: altering the core chemical composition and surface functionalization impacts the toxicity of nanomaterials to Daphnia magna. To determine whether to accept or refute this hypothesis I used the environmentally relevant model organism, Daphnia magna, and chemically tailored NMs. My results indicated that acute and chronic impacts to Daphnia upon exposure to functionalized gold NMs are strongly dependent on initial surface charge and the ligand used in the functionalization process; depending on the ligand, negative impacts are explained by the ligand choice, however with others the NM-ligand combination are required for a negative impact indicating a nanospecific effect. Positively charged gold NMs functionalized with polyallylamine hydrochloride are more toxic than negatively charged particles functionalized with citrate or mercaptopropionic acid, impacting daphnid reproduction and mortality at low part per billion concentrations. Gene expression results from Daphnia acutely and chronically exposed to these same materials show that each NM-ligand combination has a unique molecular fingerprint and that for most of the genes I explored the NM-ligand combination induces similar responses in the Daphnia as its respective ligand. Lastly, my studies demonstrate that altering the core chemical composition of complex NMs to decrease toxicity. In addition, this study indicated a nanospecific impact, as the dissolved metals found in solution could not reproduce the chronic endpoint impacts and daphnid gene expression response. Collectively, this work assisted in the development of fundamental knowledge for the factors that regulate NM toxicity and identified novel molecular pathways and responses triggered by specific alterations to complex NM surface and core properties

Lipid Corona Formation from Nanoparticle Interactions with Bilayers and Membrane-Specific Biological Outcomes

While mixing nanoparticles with certain biological molecules can result in coronas that afford some control over how engineered nanomaterials interact with living systems, corona formation mechanisms remain enigmatic. Here, we report spontaneous lipid corona formation, i.e. without active mixing, upon attachment to stationary lipid bilayer model membranes and bacterial cell envelopes, and present ribosome-specific outcomes for multi-cellular organisms. Experiments show that polycation-wrapped particles disrupt the tails of zwitterionic lipids, increase bilayer fluidity, and leave the membrane with reduced ζ-potentials. Computer simulations show contact ion pairing between the lipid headgroups and the polycations’ ammonium groups leads to the formation of stable, albeit fragmented, lipid bilayer coronas, while microscopy shows fragmented bilayers around nanoparticles after interacting with Shewanella oneidensis. Our mechanistic insight can be used to improve control over nano-bio interactions and to help understand why some nanomaterial/ligand combinations are detrimental to organisms, like Daphnia magna, while others are not. </a

Lipid Corona Formation from Nanoparticle Interactions with Bilayers and Membrane-Specific Biological Outcomes

<a></a><a>While mixing nanoparticles with certain biological molecules can result in coronas that afford some control over how engineered nanomaterials interact with living systems, corona formation mechanisms remain enigmatic. Here, we report spontaneous lipid corona formation, i.e. without active mixing, upon attachment to stationary lipid bilayer model membranes and bacterial cell envelopes, and present ribosome-specific outcomes for multi-cellular organisms. Experiments show that polycation-wrapped particles disrupt the tails of zwitterionic lipids, increase bilayer fluidity, and leave the membrane with reduced ζ-potentials. Computer simulations show contact ion pairing between the lipid headgroups and the polycations’ ammonium groups leads to the formation of stable, albeit fragmented, lipid bilayer coronas, while microscopy shows fragmented bilayers around nanoparticles after interacting with <i>Shewanella oneidensis</i>. Our mechanistic insight can be used to improve control over nano-bio interactions and to help understand why some nanomaterial/ligand combinations are detrimental to organisms, like <i>Daphnia magna</i>, while others are not. </a