news
ANALYTICAL CURRENTS A “liquid Teflon” microfluidic device The first microfluidic devices were made from glass and silicon using costly, laborintensive photolithography and etching procedures. Now, 10 years later, most microfluidic devices are fabricated by cross-linking poly(dimethylsiloxane) (PDMS), a nontoxic, flexible elastomer that easily releases from molds and is permeable to gases. Although PDMS offers many advantages, its use is limited because the material swells when exposed to most organic solvents. Joseph DeSimone and colleagues at the University of North Carolina at Chapel Hill, the California Institute of Technology, and North Carolina State University have found a new group of elastomers with all the properties of PDMS, except that they are resistant to swelling in the presence of organic solvents. Called photocurable perfluoro-
Jacket
Tuan Vo-Dinh and colleagues at Oak Ridge
a thin coating, which helps
National Laboratory have created a nano-
maintain the nanoscale di-
probe that induces surface-enhanced
ameter of the tapered tip. five different nanoprobe tips,
tion in nanoscale environments, on localized
varying the thickness of the
surfaces, and even inside cells.
silver island layer from 5 to 15 nm. They found that a
fiber tapered at one end to form a 100-nm-
10-nm-film thickness provid-
diam tip. To induce the SERS effect, the tip
ed the optimum SERS effect.
is coated with a thin layer of silver islands
(b)
100 µm
Silver island layer
Tapered nanoprobe
The researchers created
The small-scale probe allows SERS detec-
The new probe is essentially an optical
100 µm
polyethers (PFPEs), or “liquid Teflons” the new elastomers are gas permeable; have low toxicity; and are viscous oils at room temperature, much like PDMS elastomers. The researchers compared the properties of A dyed solution of dichloromethane, acetonitrile, and PFPE and PDMS. Because methanol easily passes through a channel in (a) a PFPE both substances are liquids device but not in (b) a PDMS device. at room temperature, the of dichloromethane, acetonitrile, and same fabrication methods could be used. Although the materials are similar in many methanol solution. In contrast, the same solution readily passed through a channel ways, they differed in their responses to in a PFPE device. Valves were also easily organic solvents. Whereas PDMS swelled opened and closed in a PFPE channel, to 109% by weight after 94 h of immerwhich demonstrates the material’s suitsion in dichloromethane, PFPE only ability for incorporation into microfluidic swelled by
