Paper BI+NL+NS+SS-ThM2
Utility of Lipid Membranes Assembled on Nanoparticles for Measuring Protein Membrane Interactions

Thursday, October 31, 2013, 8:20 am, Room 201 B

Nanoparticles (NPs) provide a well-defined template for preparing supported lipid membranes with controlled curvature. We have coated supported lipid bilayers and hybrid membranes on silica and gold nanoparticles. The localized surface plasmon resonance (LSPR) of gold NPs can be used to monitor the assembly of lipid layers on NPs and to monitor protein lipid interactions. The gold LSPR is very sensitive to the immediate surroundings of the nanoparticle surface and therefore provides a method to monitor the coating of lipids and subsequent conversion of a supported bilayer to a hybrid membrane after the addition of hydrophobic alkanethiols. We demonstrate that both long chain (decanethiol) and short chain (propanethiol) anchors are able to form hybrid membranes and that these membranes allow for LSPR based detection of protein binding events at the membrane surface.

While many materials have been used as membrane supports, there are unmet needs in the development of membrane mimics and it remains challenging to monitor the coating process and to control the curvature of a membrane. Recent work has demonstrated that quantum dots, silica NPs, and gold NPs can be used as templates for membranes providing an opportunity to control curvature. Here, we have exploited the local refractive index sensitivity of the gold LSPR to observe the process of lipid-coating, structural rearrangement of supported membranes into hybrid membranes, and finally the binding of protein. The introduction of phosphatidylcholine (PC) to the gold NPs results in a rapid binding evidenced by a change in the wavelength of the LSPR, however, the interaction with gold is weak and the gold is not completely covered by the lipid. By adding a hydrophobic alkanethiol anchoring group, the lipids bind closer to the gold NP surface resulting in increased stability. This stability is achieved at different concentrations for short and long hydrophobic chains. When propanethiol was used it was possible to destabilize and remove the lipid coating by adding the hydrophilic thiol, beta-mercaptoethanol. This loss of membrane is observed through changes to the LSPR and increased permeability of the membrane to ions.