Easy route to superhydrophobic copper-based wire-guided droplet microfluidic
systems.
ACS Nano, 3 (9):
2647--2652 (September 2009)DOI: 10.1021/nn900607p
Abstract
Droplet-based microfluidic systems are an expansion of the lab on
a chip concept toward flexible, reconfigurable setups based on the
modification and analysis of individual droplets. Superhydrophobic
surfaces are one suitable candidate for the realization of droplet-based
microfluidic systems as the high mobility of aqueous liquids on such
surfaces offers possibilities to use novel or more efficient approaches
to droplet movement. Here, copper-based superhydrophobic surfaces
were produced either by the etching of polycrystalline copper samples
along the grain boundaries using etchants common in the microelectronics
industry, by electrodeposition of copper films with subsequent nanowire
decoration based on thermal oxidization, or by a combination of both.
The surfaces could be easily hydrophobized with thiol-modified fluorocarbons,
after which the produced surfaces showed a water contact angle as
high as 171 degrees +/- 2 degrees . As copper was chosen as the base
material, established patterning techniques adopted from printed
circuit board fabrication could be used to fabricate macrostructures
on the surfaces with the intention to confine the droplets and, thus,
to reduce the system's sensitivity to tilting and vibrations. A simple
droplet-based microfluidic chip with inlets, outlets, sample storage,
and mixing areas was produced. Wire guidance, a relatively new actuation
method applicable to aqueous liquids on superhydrophobic surfaces,
was applied to move the droplets.