(420ad) Gold Nanoparticle Interactions with Model Biological Membranes
The unique surface area properties of nanoparticles (NPs) make them attractive for a variety of applications and industries that did not exist before, such as drug delivery applications and consumer products. However, those properties may alter their cytotoxicity posing a potential health threat with increased use ultimately leading to NP exposure and disposal within our environment. There is little information on how NPs will interact once in contact with environmental habitats and us, making it important to understand these interactions to ensure their safety.
A Quartz Crystal Microbalance with Dissipation (QCM-D) was used to create a supported lipid bilayer (SLB) formed from L-α-phosphatidylcholine (PC) on quartz crystal substrate. This SLB is representative of a typical biological membrane. This instrument allows for nano-scale readings in real time, making it ideal for our goal. The QCM-D measures frequency and dissipation changes at five overtones (3, 5, 7, 9, 11). Frequency is inversely proportional to mass changes, and dissipation results lend an understanding of surface rigidity. The overtones measured by the QCM-D give a depth perspective to our results. The 3rd overtone is indicative of the fluid furthest from the crystal and the membrane’s surface, while the 11th overtone is indicative of the fluid closest to the crystal and the furthest depth of the membrane. The diameters of gold NPs studied were 2, 5, 10, and 40 nm gold NPs at a constant concentration of 7.14*1010 particles/mL. Gold NPs were either diluted in deionized water or in poly(methacrylic acid) (PMA). NPs suspended in water were used to investigate how they would interact in a sterile lab condition, while PMA was used to understand how gold NP interactions may be altered in the presence of organic coatings. NPs will ultimately come in contact with natural organic material in the environment during disposal, having the ability to alter the NP surface potential and hydrophobicity.
When gold NPs were suspended in water, all four sizes exhibited similar results, with some variation in the 10 nm NPs. All overtones resulted in similar magnitudes, suggesting even insertion throughout the depth of the bilayer. When gold NPs were suspended in PMA, a size dependence was clearly observed, with the largest interaction occurring with 40 nm gold NPs, which exhibited significant mass removal. Our results show gold NPs in water all have a similar trend. However, once gold NPs are in contact with PMA, the mechanism for their interaction changes. The smaller size gold NPs interact with the SLB by adding small amounts of mass to the surface. This is a very different mechanism than the 10 nm and 40 nm gold NPs suspended in PMA, where mass is removed. The 10 nm gold NPs contribute to a relatively small amount of mass or lipid removal in comparison with the 40 nm gold NPs. With a SLB mass of 350.4 ng, the 40 nm gold NPs removes approximately 1/3rd of the bilayer.