Interfacial pressure and phospholipid density at emulsion droplet interface using fluorescence microscopy

Phospholipids are widely used to stabilize oil in water micron size emulsion droplets; the interfacial phospholipid density and tension of such droplets are difficult to estimate. In the present paper, we describe a simple approach by which the measurement of a micron size oil droplet interface fluorescence intensity provides directly both the interfacial phospholipid density and the interfacial tension. This method relies on two prior calibration steps: (i) the quantitative variation of the interfacial tension with fluorescence intensity at droplets interface through micro-manipulation techniques; (ii) the variation of interfacial tension with phospholipid density through monolayer isotherm. Here, we show the validity of this approach with the example of micron size oil droplets stabilized with a phosphatidylcholine phospholipid, in aqueous buffer.