Detection of lipid bilayer membranes formed on silica fibers by double-long period fiber grating laser refractometry

The formation of lipid bilayer membranes on silica optical fiber surfaces is critical to the development of new optical biosensors based on supported lipid bilayer membrane technology. This paper reports on a new long period fiber grating (LPFG) method using double gratings, one serving as the sensor and another as the reference to correct for environmental factors, to study supported lipid membranes on a silica optical fiber. A method for correcting the effect of the environmental variation on sensor responses is described. The measurements show that formation of eggPC lipid bilayer membranes on the silica optical fiber surface takes place in about 3 min, which is accompanied with about a 500 picometer decrease in the resonance coupling wavelength of the sensor grating. The formation process of eggPC lipid bilayer membranes with and without Gramicidin was measured. It was found that while the presence of Gramicidin does not affect the rate of lipid bilayer membrane formation on the silica fiber, it causes a greater decrease in the resonance coupling wavelength than pure eggPC because of the increased film refractive index. Formation of a lipid bilayer membrane on the silica optical fiber surface was verified by confocal microscopy and through fluorescence recovery after photobleaching (FRAP) analysis, confirming the formation of a single lipid bilayer on the surface of the silica fiber with a diffusion coefficient of 1.2 μ m ² s^-1.