Self-spreading Lipid Bilayer as Nanofluidic Medium for Micro- and Nanostructured Biosurface Fabrication
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1236-SS03-03
Self-spreading Lipid Bilayer as Nanofluidic Medium for Micro- and Nanostructured Biosurface Fabrication Kazuaki Furukawa and Yoshiaki Kashimura NTT Basic Research Laboratories, Atsugi, Kanagawa, 243-0198 Japan
ABSTRACT We report on the phenomenology and kinetics of a self-spreading supported lipid bilayer (SLB) on a patterned surface. Analyses of our experiments provided two findings. One is that the self-spreading velocity increased when the SLB reached the inlet of the line patterns. This capillary effect-like behavior indicates an additional attractive interaction for SLB spreading in the line patterns. The other is that the front edge is always normal to the spreading direction even for curving lines. This can be attributed to the line tension at the spreading front edge.
INTRODUCTION Self-spreading is a lipid wetting process at a solid-liquid interface that induces the spontaneous formation of a supported lipid bilayer (SLB) on a solid surface from a lump of randomly oriented lipid molecules. The phenomenology and kinetics of self-spreading on a flat surface were studied by Rädler et al. [1]. The driving force behind the spreading is the gain in energy of a hydrophilic interaction between the spreading lipid bilayer and the hydrophilic surface. In contrast, dissipation induced by friction energy imposes a penalty on spreading. When we used hydrophilic and hydrophobic pattern surfaces, we found that self-spreading occurs only on the former [2]. We also reported that a self-spreading lipid bilayer could be used as a molecule-carrying medium, which led us to propose a new type of microchannel device [2]. We demonstrated that fluorescence resonance energy transfer (FRET) efficiencies could be quantitatively determined using the device [3]. In addition, we showed that the self-spreading continued on 100 nm scale up-and-down structures [4] and through a sub-100-nm gap [5, 6]. By utilizing these techniques, we can fabricate SLB micro- and nanostructures on demand on solid surfaces. Since a self-spreading lipid bilayer is about 5 nm thick, it can or must be treated as a nanofluidic medium. However, the basic properties of self-spreading on a patterned surface have yet to be thoroughly studied. In this paper, we focus mainly on the phenomenology and kinetics of a self-spreading lipid bilayer on a patterned surface and attempt to indicate several new characteristics of a self-spreading SLB as a nanofluidic medium.
EXPERIMENT Micropattern substrates were fabricated on a SiO2 wafer by a conventional lift-off process (approximately 5 nm Ti and 45 nm Au). The patterns are shown in figure 1. One pattern consists of 2, 5, and 10 µm wide straight lines. The other pattern includes 10 µm wide curving lines, and in some places it forces the self-spreading lipid bilayer to spread in a direction opposite to the radial direction from the lipid source. The substrate was cleaned carefully in piranha and NH4F solutions to obtain a hydrophilic SiO2 surface prior to use. L-α-phosphatidylcholine (L-α-PC) extracted from eg
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