A micromachined polyimide aperture for stable bilayer lipid membranes (BLMs)

Silicon micromachining is used to fabricate reproducible miniature apertures over photosensitive polyimide (PPI) layers (septa), with highly controllable dimensions. PPI, having a high level of planarization, chemical inertness, a low dielectric constant, and good mechanical strength, is a very suitable material to be used as BLM septa. Apertures of approximately 5 mu m thickness and approximately 40 mu m diameter in PPI septa suspended over thick silicon rims were realized. The fabrication process includes double-side oxide growth on the wafer, spin-coating the PPI and its patterning, back surface anisotropic window etching, and a final cleaning step. Apertures with high circular symmetry were fabricated using this process. The BLM is formed by dropping a small amount of phospholipid-alkane solution over the PPI aperture. An initially few- mu m-thick membrane spontaneously thins down to an approximately 50 AA thick BLM. Specific capacitance measurements of these BLMs revealed stability of up to 50 h.