Microchannel Device Using Self-Spreading Lipid Bilayer as Molecule Carrier

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Kazuaki Furukawa
Materials Science Laboratory

@ @Self-spreading is a lipid wetting process at a solid-liquid interface, where a single supported lipid bilayer (SLB) is formed by a self-assembly process at the rim of a lipid spot adhering to a hydrophilic surface. We examined the self-spreading on the patterned surface and found that self-spreading occurs only on the hydrophilic surface of SiO2. This led us to propose a new type of microchannel device, which we call "lipid-flow chip" [1].
@The device structure and principle of the device operation are shown schematically in Fig. 1. The device is equipped with microchannel part of 10 ƒÊm wide and 400 ƒÊm long, and has a well on each side, which has been fabricated by conventional photolithography and lift-off process. A single self-spreading SLB grows only on hydrophilic surfaces after the SLB has been introduced into the pattern. When two SLBs collide in the middle of the channel, they form a unified SLB where molecular diffusion from one side to the other becomes dominant. SLBs are used only for transporting the molecules of interest. Thus an SLB is regarded as, for instance, a carrier gas for gas chromatography.
@The device is beneficial for detecting an intermolecular interaction. As one example, we demonstrate the observation of fluorescence resonance energy transfer (FRET) between a donor (CC2) and an acceptor (FITC). As shown in Fig. 2, two lipid bilayers containing each dye-conjugated molecule was collided with each other in the microchannel. After the collision, they form a unified lipid bilayer, and the dyes are mixed with each other by lateral diffusion. The distribution of dye concentration is symmetrical to the point of the collision. A great reduction in donor fluorescence is, however, observed in a mixed area of donor and acceptor. This is because of the two relaxation processes, emission and FRET, exists in excited donor.  The great reduction of donor emission is attributed to the effective FRET. Our device is also advantageous for quantitative analyses of FRET efficiency between a variety of dye pairs.
@We plan to apply the technique to enzymes and proteins in order to study molecular interactions such biomolecules have.

[1] K. Furukawa, et al., Lab Chip 6 (2006) 1001.
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Fig. 1. Device structure and principle of the operation. L-ƒ¿-PC extracted from egg yolk is used for the carrying medium of dye-conjugated lipid molecules.
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Fig. 2. Time-lapse observation of FRET. 5% of CC2- and FITC-conjugated lipid are mixed in L-ƒ¿-PC.

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