Fluorescence correlation and lifetime correlation spectroscopy applied to the study of supported lipid bilayer models of the cell membrane

Supported Lipid Bilayers (SLBs) are versatile models capable of mimicking some of the key properties of the cell membrane, including for example lipid fluidity, domain formation and protein support, without the challenging complexity of the real biological system. This is important both from the perspective of understanding the behaviour and role of the lipid membrane in cell structure and signalling, as well as in development of applications of lipid membranes across domains as diverse as sensing and drug delivery. Lipid and protein diffusion within the membrane is vital to its function and there are several key experimental methods used to study membrane dynamics. Amongst the optical methods are Fluorescence Recovery After Photobleaching (FRAP), single particle tracking and Fluorescence Correlation (and Fluorescence Lifetime Correlation) Spectroscopy (FCS/FLCS). Each of these methods can provide different and often complementary perspectives on the dynamics of the fluid membrane. Although FCS is well established, FLCS is a relatively new technique and both methods have undergone a number of extensions in recent years which improve their precision and accuracy in studying supported lipid bilayers, most notably z-scan methods. This short review focusses on FCS and FLCS and their recent applications, specifically to artificial lipid bilayer studies addressing key issues of cell membrane behaviour