| A method for the microfabrication of small apertures in a silicon substrate using well-known cleanroom technologies is presented. The platform can be used as a universal device to measure the electrical activity of single channels of ion channel proteins. First, 150mum apertures were etched through a silicon wafer using a plasma-etcher, which offers the advantage of precise control of the diameter and high volume throughput over the common method of drilling or burning a hole in a thin sheet of Teflon. A 75mum thick SU-8 layer was photolithographically patterned around the aperture to decrease the capacitance of the device, thus reducing the recorded noise during measurements of ion channel proteins. Reversible silver/silver chloride electrodes were integrated around the circumference of the opening and were demonstrated to provide long-term stable measurements of the ion channel currents. Finally, the device was rendered hydrophobic with chemical vapor deposition of a PTFE surface layer using the passivation step of the Bosch process. The hydrophobic properties of PTFE make it ideal for lipid bilayer experiments because it enhances the attraction between the lipid tails and substrate and enables formation of a giga-ohm seal. As each additional feature was integrated into the device, characteristic measurements of OmpF porin ion channel protein inserted into high resistance phospholipid bilayers were made with both standard silver/silver chloride wire electrodes and finally with electrodes integrated onto the surface of the silicon device. The RMS current noise of lipid bilayers suspended on the silicon device was measured and shown to be comparable to that of commercially available apertures. A novel method of measuring transmembrane ion channel conductance using a lock-in amplifier was also demonstrated with similar results on both a commercially available polystyrene bilayer cup and the fabricated silicon device. The integrated silicon device was engineered and fabricated, the measurement equipment was qualified and the software was programmed in the Center for Solid State Electronics Research at Arizona State University. |
