Abstract - Nguyen
First-principle Description of Z-Scan Fluorescence Correlation Spectroscopy and its Effects on Diffusion Measurements in Biomimetic Model Membranes
The biological membrane not only acts as the division between different cells and the cellular environment, but is also an important interface for cells to communicate. This communication involves the redistribution and exchange of molecules within the membrane facilitated by its liquidcrystalline property and low lateral friction. Molecular redistribution is primarily achieved via diffusion, wherefore its accurate determination is of central interest in many molecular studies. Fluorescence Correlation Spectroscopy (FCS) is a popular technique to investigate the lateral diffusion in lipid bilayers. Yet, in planar systems, FCS sensitively depends on the axial position of the membrane in the FCS confocal detection volume and centering the membrane therein is difficult to achieve. Here, we use the z-scan FCS approach, to track the membrane position within the confocal detection volume. We provide a first-principle theoretical description of the z-dependent autocorrelation function (ACF) andcorrelation amplitude for accurate diffusion time _D and molecular number N determination. Here, the molecular detection efficiency (MDE) instead of the commonly assumed 3D Gaussian shaped confocal volume correctly describes the beam optics. We finally validate our approach with biomembrane data of giant unilamellar vesicles (GUVs).