In an earlier entry (Tiny Bubbles), I mentioned the idea of creating logical circuits by using nanoliter droplets through a microchannel. Microfluidics and circuits use similar terminology; notably "active" and "passive." An active electronic circuit draws power (usually for an operational amplifier) to shape a signal, whereas the passive circuit can be used without a power source. The advantages of the passive unit are low cost, zero power consumption, and long-term stability. Active components efficiently shape a signal, but at a cost of requiring a power supply.

Turning back to microfluidic devices; passive components have much the same advantages as passive circuitry: easy and cheap to fabricate and maintain, and more reliable and consistent performance. Because they're cheaper to produce, the possibility of a disposable lab-on-a-chip, or μTAS (Micro-Total Analysis Systems), device is more feasible.

More specifically, the passive microvalve has proven a valuable little invention. These valves can be as simple as a rubber flap (loosely speaking), but one chip could contain thousands. In addition to valves, passive versions of micropumps, -mixers, -dispensers, and -filters are used in increasingly complex microfluidic devices.

The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. —William Bragg

I think Bragg would be excited about these types of biomicrofluidic advances. Delving further into the circuit/microdevice analogy seems worthwhile, considering the wealth of devices that are based on complex arrangements of simple circuits. How will scientists stretch this comparison further?

Will these passive components be responsible for a future torrent of advancement in the field of disease detection in third world countries? I would imagine that they will and more. There'll be an increasing number of advances in micro- and nanomechanical sensors for environmental, chemical, and biological detection as well. In addition to giving scientists new avenues for detection, the device opens up all sorts of opportunities for epidemiologists to study how a certain strain of a disease moves through a population or how a chemical spill spreads throughout a region, for example.