Studying membrane biophysics using Graphene-induced energy-transfer

Graphene-induced energy transfer (GIET) was recently introduced for sub-nanometric axial localization of fluorescent molecules. GIET exploits the near-field energy transfer from an excited fluorophore to a single sheet of graphene. This alters the fluorescence decay-time of the emitter and can be easily determined by fluorescence lifetime imaging microscopy (FLIM). The axial resolution of GIET implies to study of biological membranes. We present the measurement of the thickness of synthetic model membranes and demonstrate changes upon the addition of cholesterol. Furthermore, we are able to show the flipping of lipids from one leaflet to the other and determine the rates of this dynamics. In addition, we used GIET for mapping quasi-stationary states of the mitochondrial membranes before and during ATP synthesis. Upon activation, the inner membrane clearly approaches the outer membrane and the inter-membrane space is reduced by ∼2 nm.