Tiny Whirlpools to Corral Microbes

The theory behind the technology, called rapid electrokinetic patterning - or REP - has been described in technical papers published between 2008 and 2011. Now the researchers have used the method for the first time to collect microscopic bacteria and fungi, said Steven T. Wereley, a Purdue University professor of mechanical engineering.

The technology could bring innovative sensors and analytical devices for lab-on-a-chip applications, or miniature instruments that perform measurements normally requiring large laboratory equipment. REP is a potential new tool for applications including medical diagnostics; testing food, water and contaminated soil; isolating DNA for gene sequencing; crime-scene forensics; and pharmaceutical manufacturing.

"The new results demonstrate that REP can be used to sort biological particles but also that the technique is a powerful tool for development of a high-performance on-chip bioassay system," Wereley said.

The technology works by using a highly focused infrared laser to heat a fluid in a microchannel containing particles or bacteria. An electric field is applied, combining with the laser's heating action to circulate the fluid in a "microfluidic vortex," whirling mini-maelstroms one-tenth the width of a human hair that work like a centrifuge to isolate specific types of particles based on size.

Particles of different sizes can be isolated by changing the electrical frequency, and the vortex moves wherever the laser is pointed, representing a method for positioning specific types of particles for detection and analysis.

The researchers used REP 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 new findings demonstrate the tool's ability to perform size-based separation of microorganisms, Wereley said.

"By properly choosing the electrical frequency we can separate blood components, such as platelets," Wereley said. "Say you want to collect Shewanella bacteria, so you use a certain electrical frequency and collect them. Then the next day you want to collect platelets from blood. That is going to be a different frequency. We foresee the ability to dynamically select what you will collect, which you could not do that with conventional tools."

COMPAMED.de; Source: Purdue University