January 8, 2013
WEST LAFAYETTE, Ind. – Researchers have demonstrated a new
technology that combines a laser and electric fields to create tiny
centrifuge-like whirlpools to separate particles and microbes by size, a
potential lab-on-a-chip system for medicine and research.
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.
A research paper about the technology was featured on the
cover of the Dec. 7 issue of Lab on a
Chip magazine, and the work is highlighted as a news item in the Jan. 13
issue of Nature Photonics, posted
online Dec. 27. Mechanical engineering doctoral student Jae-Sung Kwon, working
extensively with Sandeep Ravindranath, a doctoral student in agricultural and
biological engineering, was lead author of the Lab on a Chip paper.
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.
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
The Lab on a Chip
paper was written by Kwon; Ravindranath; Aloke Kumar, a researcher at the Oak
Ridge National Laboratory; Joseph Irudayaraj, a Purdue professor of
agricultural and biological engineering and deputy director of the Bindley
Bioscience Center; and Wereley.
Much of the research has been based at the Birck
Nanotechnology Center in Purdue’s Discovery Park, in collaboration with
Irudayaraj’s group in the Bindley Bioscience Center.
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,” 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.”
The overall research field is called “optoelectrical
microfluidics.” More research is needed before the technology is ready for
“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.”
REP may be used as a tool for nanomanufacturing because it
shows promise for the assembly of suspended particles, called colloids. The
ability to construct objects with colloids makes it possible to create
structures with particular mechanical and thermal characteristics to manufacture
electronic devices and tiny mechanical parts.
Purdue researchers are pursuing the technology for
pharmaceutical manufacturing, Wereley said, because a number of drugs are
manufactured from solid particles suspended in liquid. The particles have to be
collected and separated from the liquid. This process is now done using filters
REP also might be used to diagnose the presence of
viruses, as well, although it has not yet been used to separate viruses from a
sample, Wereley said.
Unlike conventional tools, REP requires only tiny samples,
making it potentially practical for medical diagnostics and laboratory
Writer: Emil Venere, 765-494-4709, [email protected]
Sources: Steven T.
Wereley, 765-494-5624, [email protected]
Irudayaraj, 765-494-0388, [email protected]
Kumar, 865-574-8661, [email protected]
Related web site:
Lab on a Chip on Twitter
Note to Journalists: An
electronic copy of the research paper is available from the journal or by
contacting Emi Venere, Purdue News Service, at 765-494-4709, [email protected]
Manipulation for High-Performance On-Chip Bioassays
Kwon,a Sandeep P. Ravindranath,b Aloke Kumar,c
Joseph Irudayarajb and Steven T. Wereley*a
of Mechanical Engineering and Birck Nanotechnology Center, Purdue University
of Agricultural and Biological Engineering and Bindley Bioscience Center,
Division, Oak Ridge National Laboratory
first demonstrates bio-compatibility of a recently developed
opto-electrokinetic manipulation technique, using microorganisms. Aggregation,
patterning, translation, trapping and size-based separation of microorganisms
performed with the technique firmly establishes its usefulness for development
of a high-performance on-chip bioassay process. Ultimately fast and precise
on-chip manipulation of microorganisms aids in development of high-performance