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In life, we sort soiled laundry from clean; ripe fruit from rotten. Two
Johns Hopkins engineers say they have found an easy way to use gravity or
simple forces to similarly sort microscopic particles and bits of biological
matter—including circulating tumor cells.
In the Physical Review Letters, German Drazer, an assistant
professor of chemical and biomolecular engineering, and his doctoral student,
Jorge A. Bernate, reported that they have developed a lab-on-chip platform,
also known as a microfluidic device, that can sort particles, cells, or other
tiny matter by physical means such as gravity. By moving a liquid over a series
of micron-scale high diagonal ramps—similar to speed bumps on a road—the device
causes microscopic material to separate into discrete categories, based on
weight, size, or other factors, the team reported.
The process described in the journal article could be used to produce a
medical diagnostic tool, the Whiting School of Engineering researchers say. “The ultimate goal is to develop a simple device that can be used in routine
checkups by health care providers,” said doctoral student Bernate, who is lead
author on the paper. “It could be used to detect the handful of circulating
tumor cells that have managed to survive among billions of normal blood cells.
This could save millions of lives.”
Ideally, these cancer cells in the bloodstream could be detected and
targeted for treatment before they’ve had a chance to metastasize, or spread
cancer elsewhere. Detection at early stages of cancer is critical for
successful treatment.
How does this sorting process occur? Bernate explained that inside the
microfluidic device, particles and cells that have been suspended in liquid
flow along a “highway” that has speed bump-like obstacles positioned
diagonally, instead of perpendicular to, the path. The speed bumps differ in
height, depending on the application.
“As different particles are driven over these diagonal speed bumps, heavier
ones have a harder time getting over than the lighter ones,” the doctoral
student said. When the particles cannot get over the ramp, they begin to change
course and travel diagonally along the length of the obstacle. As the process
continues, particles end up fanning out in different directions.
“After the particles cross this section of the ‘highway,'” Bernate said, “they end up in different ‘lanes’ and can take different ‘exits,’ which allows
for their continuous separation.”
Gravity is not the only way to slow down and sort particles as they attempt
to traverse the speed bumps. “Particles with an electrical charge or that are
magnetic may also find it hard to go up over the obstacles in the presence of
an electric or magnetic field,” Bernate said. For example, cancer cells could
be “weighted down” with magnetic beads and then sorted in a device with a
magnetic field.
The ability to sort and separate things at the micro- and nanoscale is
important in many industries, ranging from solar power to biosecurity. But
Bernate said that a medical application is likely to be the most promising
immediate use for the device.
Source: Johns Hopkins University
