Cell Membrane State, Permeability, and Elasticity Assessment for Single Cells and Cell Ensembles.

The phase state and especially phase transitions of synthetic lipid membranes are known to drastically modulate mechanical membrane properties like permeability and bending modulus. Although the main transition of lipid membranes is typically detected employing differential scanning calorimetry (DSC), this technique is not suitable for many biological membranes. Moreover, often single cell data on the membrane state or order is of interest. We here first describe how to use a membrane polarity-sensitive dye, Laurdan, to optically determine the order of cell ensembles over a wide temperature range from T = -40 °C to +95 °C. This allows to quantify the position and width of biological membrane order-disorder transitions. Second, we show that the distribution of membrane order within a cell ensemble allows for correlation analysis of membrane order and permeability. Third, combining the technique with conventional atomic force spectroscopy allows for the quantitative correlation of an overall effective Young's modulus of living cells with the membrane order.