Electro Optical Technique Generates Whirlpools to Separate Microorganisms by Size

Rapid electrokinetic patterning used to collect a bacterium Shewanella oneidensis. (Purdue University image)

The business of sifting out specific microorganisms from a liquid sample for disease diagnosis is a difficult difficult task, especially when you want a system that can spot just about any bug out there. A new technology that uses lasers and well controlled electric fields to create tiny whirlpools has shown effective in filtering out tiny quantities of bacteria and fungi from the rest of the sample.

Called rapid electrokinetic patterning (REP), the technique has been getting perfected by researchers from Purdue University and Oak Ridge National Laboratory over the last three years. Now after a bit of experience with the system, the team is able to perform “aggregation, patterning, translation, trapping and size-based separation of microorganisms.”

From Purdue:

The technology works by using a highly focused infrared laser to heat 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.

Here the rapid electrokinetic patterning technique is used to arrange bacteria into a specific pattern. (Purdue University image)

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, [Steven T. Wereley, professor of mechanical engineering at Purdue], said.

“By properly choosing the electrical frequency we can separate blood components, such as platelets,” he 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’s going to be a different frequency. We foresee the ability to dynamically select what you will collect, which you could not do with conventional tools.”

Purdue press release: New biochip technology uses tiny whirlpools to corral microbes

Study in Lab on a Chip: Opto-electrokinetic manipulation for high-performance on-chip bioassays

News item in Nature Photonics: Optofluidics: On-chip bioassay