Sum Frequency Generation Spectroscopy of Interactions at Model BiointerfacesPublic Deposited
The expanding use of nanomaterials in consumer products challenges scientists to understand the impact of these materials before their inevitable release into the environment. In the same way that the widespread use of DDT and asbestos has caused unforeseen negative impacts on both the environment and on human health, the increasing incorporation of nanotechnology in our daily lives has the potential to significantly alter ecosystems unless a deeper knowledge of these materials is developed. The Center for Sustainable Nanotechnology (CSN) has accepted this challenge and aims to develop an understanding of the interactions of nanomaterials with the environment in order to predict and control these interactions. As a part of the effort of the CSN, the work presented in this thesis explores the nano-biointerface primarily using Sum Frequency Generation (SFG) spectroscopy, a technique which is well-suited for targeting and observing molecular changes at interfaces. An exploration of SFG spectroscopy of supported lipid bilayers (SLBs), used as model cell membranes, finds that SFG signals from SLBs heavily depend on the transition temperature of the component lipids and the experimental temperature. This result points towards the future use of SFG spectroscopy to discover bilayer phase changes due to interactions with nanomaterials. In addition, this study highlights the strengths of a broadband SFG system over a scanning SFG system. SFG spectroscopy is utilized along with a suite of other techniques in order to examine the formation of a lipid corona around a nanomaterial. In determining that the lipid corona forms around a nanoparticle of either gold or nanodiamond core composition with the positively charged ligand, poly(allylamine hydrochloride) (PAH), and that the creation of contact ion pairs plays a role, this research lays the foundation for future multidisciplinary studies on the nano-biointerface. Additional research on the interactions of PAH with lipid monolayers on oil droplets illustrates two main pathways of interaction which are dependent on the concentrations of PAH and NaCl, showing that controlling solution conditions is just one lever to use in the control of nanomaterial interactions. From understanding a spectroscopic technique used in an uncommon way under challenging conditions, to using this technique to understand a complex biochemical interaction at the nano-biointerface, to discovering a potential way to control these interactions, this thesis demonstrates how spectroscopy, coupled with complementary techniques under the direction of talented scientists, can effectively explain important biophysical phenomena.