Photolithographic
Fabrication of Microapertures with
Well-Defined, Three-Dimensional Geometries for Suspended Lipid Membrane
Studies
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Abstract
Robust and high-density biosensors
incorporating suspended lipid
membranes require microfabricated apertures that can be readily integrated
into complex analysis systems. Apertures with well-defined, three-dimensional
geometries enable the formation of suspended lipid membranes and facilitate
reduced aperture size compared to vertical-walled apertures. Unfortunately,
existing methods of producing apertures with well-defined, three-dimensional
geometries are based on complex and expensive fabrication procedures,
some of which yield apertures in excessively fragile thin-film materials.
Here, we describe a microfabrication method utilizing incline and
rotate lithography that achieves sloped-wall microapertures in SU-8
polymer substrates with precision control of the aperture diameter,
substrate thickness, and wall angle. This approach is simple, is of
low cost, and is readily scaled up to allow highly reproducible parallel
fabrication. The effect of the incident angle of UV exposure and the
size of photomask features on the aperture geometry were investigated,
yielding aperture diameters as small as 7 μm and aperture wall
angles ranging from 8° to 36° measured from the normal axis.
Black lipid membranes were suspended across the apertures and showed
normalized conductance values of 0.02–0.05 pS μm<sup>–2</sup> and breakdown voltages of 400–600 mV. The
functionality of the resulting sloped-wall microapertures was validated
via measurement of reconstituted α-hemolysin activity and the
voltage-gated channel activity of alamethicin