Interferometric Gated Off-Axis Reflectometry (iGOR) - A Label Free Method to Measure Lipid Membrane Dynamics and Deduce Biophysical Properties

The function and organisation of proteins within the cell membrane is a fundamental area within cell biology, underpinning key processes. When investigating the interaction between proteins and lipid membranes, it is important to consider a dynamic system, as proteins and membrane phase behaviour are known to modulate the function of each other [1]. However, due to limits in technology, the study of membrane dynamics often falls short, especially when evaluating thickness and curvature. Traditional fluorescence methods suffer from photobleaching and phototoxicity [2]. Label-free techniques like iSCAT and mass photometry allow the observation of membrane components on a supported lipid bilayer which inevitably dampens fluctuations of the membrane [3], [4]. We have developed a technique, Interferometric gated off-axis reflectometry (iGOR), to alleviate these limitations by facilitating precise observation of a section of suspended lipid membrane. iGOR is a form of digital holography (see Fig. 1a,c) in which we combine measurements of membrane thickness and height to analyse membrane stiffness and phase transitions using thermal fluctuations. To maximise the temporal resolution our system acquires at 327Hz with an exposure time of 3ms.