Whenever scientists want to separate specific particles from the liquid in which they’re found, it usually involves a fairly large centrifuge. In the laboratory, for example, spinning machines cause heavier particles to collect at the bottom of a test tube for extraction. Other machines spin blood around in order to suck out platelets, plasma or other bits, according to their mass. Meanwhile, those pesky Iranians are using centrifuges to separate different isotopes of uranium for their nuclear program.
One thing all of these examples have is that the machines involved are rather large – bigger than a breadbasket, you might say. But no longer. Those engineering geniuses over in West Lafayette, Indiana have figured out a way to cut the size of this separating technique to a fraction of a human hair.
The technique involves the use of a heating laser and electric fields. By pointing a laser at a specific spot of fluid within a microchannel, the fluid heats up and gains the energy to start moving. Think boiling water or steam causing the pistons in a train to move. Hot liquids don’t stand still. Next, an electric field is applied, causing the liquid to begin rotating in a “microfluidic vortex.” The frequency of the field applied allows for the selection of differently sized particles, while pointing the laser at different spots allows for the selection of the area the particles are separated in.
This idea has been around and gaining traction since 2008. The impressive thing here is that the researchers were able to miniaturize it, creating a system that works on a scale just one-tenth the diameter of a human hair.
The applications are boundless. Instead of needing large machines to test blood samples, for example, individual microchips could be manufactured to take care of the entire process on the scale of a fingernail. It could be used for medical diagnostics, testing food, water, and contaminated soil, isolating DNA for gene sequencing, crime-scene forensics, pharmaceutical manufacturing, and more.
In the recent study, the team proved their setup works by using it to collect three types of microorganisms: a bacterium called Shewanella oneidensis MR-1; Saccharomyces cerevisiae, a single-cell spherical fungus; and Staphylococcus aureus, a spherical bacterium. The test demonstrates the tool’s ability to perform size-based separation of microorganisms.
The paper, “Opto-Electrokinetic Manipulation for High-Performance On-Chip Bioassays,” was published in Lab on a Chip by Purdue University researchers Steven T. Wereley, Jae-Sung Kwon, and Sandeep P. Ravindranath; Aloke Kumar, a researcher at the Oak Ridge National Laboratory; and Joseph Irudayaraj, a Purdue professor of agricultural and biological engineering and deputy director of the Bindley Bioscience Center.