Laser/electrical combination separates particles by size

Researchers have demonstrated a new technology that combines a laser and electric fields to create centrifuge-like whirlpools to separate particles and microbes by size, a potential lab-on-a-chip system for medicine and research.

The development could lead to a potential lab-on-a-chip system and the theory behind the technology, rapid electrokinetic patterning (REP), has been described in technical papers published between 2008 and 2011.

Now researchers in the US have used the method for the first time to collect bacteria and fungi, said Steven T Wereley, a Purdue University professor of mechanical engineering.

According to a statement, 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 fluid in a micro-channel containing particles or bacteria. An electric field is applied, combining with the laser’s heating action to circulate the fluid in a microfluidic vortex 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 from Purdue and Oak Ridge National Laboratory used REP to collect three types of micro-organisms: 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 micro-organisms, 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’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.’

More research is needed, however, before the technology is ready for commercialisation.

‘It won’t be on the market in a year,’ Wereley said. ‘We are still in the research end of this. We are sort of at the stage of looking for the killer app for this technology.’

A research paper about the technology was published in the 7 December 2012 issue of Lab on a Chip. Mechanical engineering doctoral student Jae-Sung Kwon, working with Sandeep Ravindranath, a doctoral student in agricultural and biological engineering, was lead author of the paper.