Gold nanoparticles are at the forefront of technology advances and drug delivery applications; however, there is still little knowledge on their toxicity. Our studies use a Quartz Crystal Microbalance with Dissipation to measure nanoparticle-membrane interactions. This assay allows us to look at the changes these nanoparticles have on model biological membranes in terms of frequency and dissipation results. By applying mathematical models, we are able to obtain further insight through looking at the membrane's mass changes due to contact with nanoparticles. Specifically, we investigated the size dependence of these gold nanoparticles while suspended in water and natural organic matter. Our method allows us to examine nanoparticle toxicity and insertion mechanisms, which provides insight on safe drug delivery technique.