Interferometric UV lithography: from optical fibers to biomembranes

Interferometric Lithography is used to produce sub-micron scale periodic structures in glass optical fibers as well as biomembranes and other substrates of biological interest. Normal as well as slanted Bragg-gratings fabricated by this technique within the core of optical fibers are fabricated and used for health monitoring/distributed sensing in carbon-polymer composite structures. Interferometric UV lithography is also used to produce microarrays on phospholipids bilayer membranes as well as other polymer substrates. Phospholipids are one of the major constituents of biological cell membranes and lipidic films have found extensive uses as simple models of cell membranes. Model biomembranes are known to be excellent platforms for biosensing.

The experiments described here were motivated by the promise of interferometric techniques to extend membrane photolithography to produce nanometer scale features. Holographic gratings and microarrays are recorded in azo-dye (NBD)-labeled phospholipid thin films using 244 nm UV light. Diffraction efficiency of these gratings shows extreme sensitivity to humidity and can increase reversibly by two orders of magnitude in air, which is saturated with water vapor. This effect is related to the unique characteristics of phospholipid molecules to undergo hydration-dependent structural reorganizations and self-assembly. Using established techniques, diffraction characteristics of the membrane-grating can be made sensitive to molecules recognized by a biological probe immobilized on the bilayer. Interferometric lithography can give much finer engineering of biomembranes than can be accomplished with use of masks. This has the potential for high-density biosensor designs.

Dr. Anup Sharma
Department of Physics, Alabama A&M University