Mechanically Stable Free-Standing Bilayer Lipid Membranes in Microfabricated Silicon Chips
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Mechanically Stable Free-Standing Bilayer Lipid Membranes in Microfabricated Silicon Chips Azusa Oshima1, Ayumi Hirano-Iwata1,2, Yasuo Kimura3, Michio Niwano1,3 1 Graduate School of Biomedical Engineering, Tohoku University, 6-6 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan 2 PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama, 332-0012, Japan 3 Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Sendai, Miyagi, 980-8577, Japan ABSTRACT In this paper, we will discuss our recent approaches for improving the mechanical stability of free-standing bilayer lipid membranes (BLMs) by combining with BLM formation and microfabrication techniques. BLMs were prepared across a microaperture fabricated in a silicon (Si) chip and their mechanical stability and electric properties were investigated. BLMs suspended in a thin Si3N4 septum showed a dramatic improvement of BLM stability. The BLMs were resistant to voltage of ±1 V and the membrane lifetime was 15- ~40 h with and without incorporated channels. The membrane containing gramicidin channel exhibited tolerance to repetitive solution exchanges. At first, electric properties of the BLMs, such as noise level and current transient, were necessary to be improved. However, after coating the chip with insulator layers of Teflon and SiO2, total chip capacitance was reduced, leading to noise reduction (1-2 pA in peak-to-peak after low-pass filtering at 1 kHz) and elimination of current transients (< 0.5 ms). Since the vicinity of the aperture edge was remained uncoated, the BLMs formed in the Si chips still showed high mechanical stability after the insulator coatings. The mechanically stable BLMs having electric properties suitable for recording activities of biological channels will open up a variety of applications including high-throughput analysis of ion-channel proteins. INTRODUCTION Ion-channel proteins are of great interest as subjects of basic physiological studies and main targets of drug discovery. Reconstitution of channel proteins in free-standing bilayer lipid membranes (BLMs) provides an excellent system for drug screening under chemically controlled conditions. In addition, channel proteins incorporated in BLMs are useful for designing highly sensitive biosensors. However, mechanical instability of BLMs hinders their applications and confines the bilayer method to laboratory use. Extensive studies have been made to improve the stability of free-standing BLMs by preparing BLMs in microfabricated devices [1]. These efforts led to prolonged membrane lifetime of several tens of hours [2]. However, mechanical stability of the BLMs has not been improved to the desired extent. In this paper, we will discuss our recent approaches for preparation of stable BLMs through the combination of silicon (Si) microfabrication techniques and BLM formation [3,4]. The stability of the BLMs was characterized in terms of resistance to mechanical and electrical shocks, membrane life
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