Researchers
at Yale have demonstrated a device that uses a magnetic liquid to separate
blood cells based on their size and shape in just minutes.
The device
applies a magnetic field to a liquid containing magnetic nanoparticles. The nanoparticles
create waves that carry cells along depending on their size, shape and mechanical
properties. The researchers, led by electrical engineering professor Hur Koser,
hope to develop a cheap alternative to cell-sorting techniques that are time-consuming
and sometimes require expensive labeling.
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Liquid suspensions
of magnetic particles, called ferrofluids, are already used as industrial
lubricants and in loudspeakers and computer hard disks. These liquids typically
contain other chemicals to keep the particles from clumping together and from coming
out of the suspension. Magnetic nanoparticles are also being explored for
cancer therapies and as contrast agents for magnetic resonance imaging (MRI)–both
applications that require very low concentrations.
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But the Yale
group is the first to make a high-concentration, biocompatible ferrofluid that doesn’t
contain any chemicals that are harmful to cells, yet still keeps the particles
afloat. “It was very tricky to find the parameters to maintain live
cells,” says Koser.
In
experiments described this week in the Proceedings of the National Academy of Sciences, the Yale
researchers made microfluidic channels lined with magnetic-field-generating
electrodes. Cells were then added to a ferrofluid in the channel. When magnetic
fields were applied along the device, the particles in the fluid pushed the
cells along the channel, separating them by size and shape. Something similar
can be accomplished using electrical fields, says Koser, but this can damage the
cells. His group used the device to separate live blood cells from sickle cells
and bacteria.
Koser
believes the device could be especially helpful when trying to detect very rare
types of blood cell, such as cancerous ones. Rapidly sorting cells using magnetic
fields could improve the sensitivity of tests for these rare cells without
adding any costly chemical labels. Tumor cells are squishier than healthy
ones–possibly because they grow quickly and so don’t form a proper internal
cell skeleton–and Koser hopes that magnetic fields will also be able to
separate cells based on their elasticity and other mechanical properties.
“The
next step is to try this in conjunction with existing sensors to improve their
sensitivity and cut down on time,” says Koser.
In the video
below, a magnetic field creates waves in a liquid containing magnetic
nanoparticles (the nanoparticles are not visible) to separate two types of
microbeads based on their size.