Towards Far-Field Microscopic Imaging of Supported Lipid Bilayer Optical Anisotropy

Abstract

The characterization of lipid bilayers is of great importance to biology as they are omnipresent in cellular organisms. Frequently, fluorescent dyes are used to observe and characterize lipid membranes.1 However, often questions can be raised regarding potential unintended interference of fluorescent dyes with the biological system under investigation. Polarimetry and in particular imaging ellipsometry has proven to be a non-disruptive characterization technique for supported lipid bilayers.2Here, a novel label-free characterization scheme for supported lipid bilayers (SLB) is presented, based on the accurate determination of spatially resolved optical anisotropy. Experimental feasibility is demonstrated for spatially resolved optical anisotropy measurements of supported lipids bilayers over a large ∼200μm2 field of view with microscopic resolution. Through a combination of spectroscopic imaging ellipsometry and liquid phase atomic force microscopy, non-destructive optical characterization of lipid bilayers without the use of external markers such as fluorescent labels is achieved. Optical anisotropy results for a DOPC/DOPS 4:1 lipid mixture are in-line with other experimental observations, but are limited in experimental error due to the presence of excess noise. Possible hard- and software improvements to achieve experimental noise reduction are contemplated.1. M.T.Z. Spence and I.D. Johnson, The Molecular Probes Handbook A Guide to Fluorescent Probes and Labeling Technologies, Live Technologies Corporation, 2010.2. E.I. Goksu, J.M. Vanegas, C.D. Blanchette, W.-C. Lin and M.L. Longo, Biochimica et Biophysica Acta, 2009, 1788, 254-266.