Volume 23 Issue 1 - December 28, 2012 PDF
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A Microchip Fabricated with a Vapor-Diffusion Self-Assembled-Monolayer Method to Transport Droplets Across Superhydrophobic to Hydrophilic Surfaces
Yu-Hsuan Lai1, Jing-Tang Yang1, and Dar-Bin Shieh2,*
1 Department of Mechanical Engineering, National Taiwan University, Taipei 106, Taiwan.
2 Institute of Oral Medicine, National Cheng Kung University, Tainan 701, Taiwan
 
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A novel method which combines microstructure patterning and SAM techniques to fabricate a microchip across superhydrophobic to hydrophilic surface to transport a droplet is proposed. The gradient from superhydrophobic to low hydrophilic surface is formed by a saturated decyltrichlorosilane(DTS) assembled on the microstructure gradient surface with the decreasing density. On the other hand, the gradient from low hydrophilic to hydrophilic surface is generated by a gradient of decyltrichlorosilane(DTS) assembled on a smooth surface. Here, a saturated decyltrichlorosilane(DTS) SAM is produced by a immersion method and a gradient of decyltrichlorosilane(DTS) SAM is produced by a vapor-diffusion method. This way overcomes the traditional limitation of a commonly used vapor-diffusion method, but retains its facility. The platform fabricated by this way has a water-contact angle from 151.2 ° to 39.7 °, and the self-transport distance is increased to about 9 mm. Moreover, a double-directional gradient that changes the moving direction of a droplet is realized by using this fabrication method. This platform is valuable not only to transport a fluid for a long distance but also for further biomedical applications, such as protein adsorption and cell adhesion and diagnostic biochips. This SAM-based surface-modification technique allows integration of switchable wettability surface in a biosensor.
Fig 1. The diagrams of (a) the immersion/vapor-diffusion SAM method, (b)the microstructure patterning on a chip,(c )the microstructure patterning obtained by SEM,(d)a droplet on suface in the mode of Cassie and Baxter.
Fig 2. Motion of a droplet on a superhydrophobic to hydrophilic gradient surface.
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