I gather that it's challenging constructing microchannels and microdevices. Like building canals and tiny dams, only they are embedded with sorting mechanisms and mixing devices. The analogy between microfluidic devices and systems of rivers, streams, and lakes only goes so far, though. When's the last time you stood on the bank near two converging rivers and watched as barges were distributed to the tributaries based on their response to an optical field?

I'm thinking of rivers and bodies of water, only because I was recently lucky enough to attend the 2008 ACS Spring Meeting in New Orleans. Approaching the city from the air, looking down on the marshland that surrounds it, you quickly realize: there's a lot of water in New Orleans. But after landing, it seems there may be other liquids that the locals prefer to drink, but I digress. If you walk along the boardwalk, the Mississippi River comes only a few feet from touching your feet. It's a little off-putting because you have to climb up several feet of steps to get to that height. All of this is a reminder that the entire city lies beneath sea level. Sorry, there I go again with a digression.

To build a complex system of micro-waterways, experimenters need to utilize some complicated tools. Building high-aspect-ratio micro channels can be facilitated with the use of Deep Reactive Ion Etching (DRIE), or plasma etching, which can be used to create channels, cavities, and sieves in MEMS and other microfluidic devices. DRIE allows for features with aspect ratios of at least 30:1, perfect for building a lot of interesting devices and such. In MEMS, the results can look impressive, especially if you're trying to construct something like this Torsional Ratcheting Actuator (Courtesy of Sandia National Laboratories [www.mems.sandia.gov]).

Two specific technologies—HARPSS (High Aspect Ratio combined with Poly and Single-crystal Silicon) and HEXSIL (HEXagonal honeycomb polySILicon)—employ DRIE to specific ends. HEXSIL—as you might guess from the name—can be used to build deep honeycomb-shaped structures, while HARPSS can be employed to build capacitive, and related, microdevices.

For another interesting look at microfluidics, I suggest this Physics Today article. This kind of information may be more helpful to me as I attempt to learn more about biomicrofluidics, than to experienced researchers or the general public. However, I don’t think there's anything wrong with an open discussion of a topic.

Anyway, I do believe I'm going to need to head back to New Orleans soon for some "research" on "fluid" flow.