Interaction of Gold Nanoparticles with a Supported Lipid Bilayer Using Quartz Crystal Microblance with Dissipation Public
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Nanoparticle toxicity has become a major topic of interest due to the inevitable exposure of these nanomaterials to both humans and the environment. Nanotechnology is a rapidly growing industry with diverse material resources and an extensive market for commercialization and introduction of nanomaterials into consumer products. The problem with this flourishing technology is that it has far outgrown research based on the safety and toxicity of the nanomaterials, which in bulk are generally nontoxic. The need for research in determining the toxic effects on cells and the implications it may have on the environment have grown but the different techniques, cell systems and nanoparticles employed are generally to diverse and conflicting in overall results that determination toxicity is nearly impossible. The need for a universal technique to study the interaction of nanoparticles with cells and decouple the molecular effects (chemical properties) from the â€œnanospecificâ€ effects (including size, concentration, surface charge, functionality and polarity) is apparent. It is additionally necessary to determine the mechanisms associated with nanoparticle-induced cytotoxicity in order to better understand the problems posed to both human and environmental health and then develop new safer nanoparticles. Therefore, the focus of this study is to determine the nano-specific (physical) properties, including size and functionalization that cause toxicity, specifically through interaction with a cell membrane. A supported lipid bilayer (SLB) composed of L-Î±-phosphatidylcholine (egg PC) was used as a model cell membrane to test the effects of 2, 5, 10 and 40 nm gold nanoparticles (AuNPs). Given the imminent exposure of nanoparticles to the environment it is important to determine how nanoparticles would behave in the presence of natural organic matter or polymers which are naturally present in environmental systems. Poly(methacrylic acid) (PMA) can be used to represent the polymers normally found in the environment. AuNPs were diluted in PMA in order to simulate fundamental environmental conditions. Analysis was done using a quartz crystal microbalance with dissipation (QCM-D), which measures the frequency (f) and dissipation (D) changes directly associated with mass and conformation changes of the SLB. Different overtones for f and D allow for theoretical interpretation of changes correlated to different layers of the membrane. The 2 and 5 nm particles were found to interact strongly with the lipid bilayer by adsorbing to and/or partially/completely penetrating into the lipid bilayer presumably due to a hydrophobic coating caused by PMA adsorption to the NP surface. The penetration caused a much more rigid membrane due to higher lipid packing caused by nanoparticle addition. The 10 and 40 nm particles interaction with the bilayer were not affected by the presence of PMA. Both AuNP sizes removed mass from the membrane with losses similar in de-ionized water and PMA solution. Removal of membrane mass (lipids/hydration) caused a more flexible membrane. It was determine that sized is the limiting factor for nanoparticle solubilization into the membrane. It can be concluded from the results that size coupled with natural organic matter affects the cytotoxicity of the nanoparticles to the membrane. A study was done with 12 nm functionalized AuNPs in the presence of humic acid, a well-known and more complex and realistic model for natural organic matter. A PC lipid bilayer was used to simulate a model cell membrane and QCM-D techniques were utilized in the determination of toxicity and mechanistic interaction of nanoparticles with a lipid bilayer. Functionalized AuNPs were shown to decrease the rigidity of the lipid bilayer by increasing the dissipation and decreasing the mass associated with the adsorbed film (SLB). The presence of humic acid stabilized the nanoparticles and provided increased electrostatic repulsion which resulted in decreased mass losses from the membrane and much smaller decreases in membrane rigidity. It was concluded that presence of humic acid reduces the effects of functionalized nanoparticle interaction with a lipid bilayer. These results may mean that natural organic matter has the ability to reduce the cytotoxic effects of nanoparticles released into the environment. Overall, the QCM-D was found to provide valuable information regarding the possible toxic properties and mechanisms in which different gold nanoparticle interact with a supported lipid bilayer under environmental conditions. The information provided by the studies performed has shed much light on the interaction of gold nanoparticles with a supported lipid bilayer in the presence of model natural organic matter. The experiments done in this study are the first steps towards developing an assay with the ability to determine the toxic physical properties and mechanisms by which nanoparticles interact with lipid bilayers will greatly aid in development of non-toxic nano-materials. The technology and techniques used in this study will greatly improve the field by solidifying one technique to use in the quantitative approach studying nanoparticle/cell interactions. The use of AFM techniques in conjunction with the QCM-D would be highly beneficial by facilitating better understanding of the exact mechanisms by which nanoparticles induce cytotoxicity.
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