Micropipet Writing Technique for Production of Two-Dimensional Lipid Bilayer Nanotube−Vesicle Networks on Functionalized and Patterned Surfaces

We present a micropipet-assisted writing technique for formation of two-dimensional networks of phospholipid vesicles and nanotubes on functionalized and patterned substrates. The substrates are patterned with vesicle-adhesive circular spots (5−7.5 μm in diameter) consisting of a basal layer of biotin on gold and an apical coating of NeutrAvidin in a sandwich manner. The area surrounding the adhesive spots is coated with a phosphatidylcholine bilayer membrane, preventing protein and liposome adhesion. Networks were formed by aspirating a biotin-functionalized giant unilamellar or multilamellar liposome (5−50 μm in diameter) into a ∼3 μm inner diameter borosilicate glass micropipet. By using a pressurized-air microejection system, a portion of the liposome is then ejected back into the solution while forming a first vesicle ∼3 μm in diameter. This vesicle is placed on an adhesive spot. When the micropipet is moved, a nanotube connection is formed from the first vesicle and is pulled to the next adhesive spot where a second vesicle is ejected. This procedure can then be repeated until the lipid material is consumed in the pipet. The method allows for formation of networks with a large number of nodes and vertexes with well-defined geometry and surface adhesion, and represents a first step toward very large scale integration of nanotube−vesicle networks in, for example, nanofluidic applications.