[Paleopsych] Laser beams sort stem cells by springiness
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Thu Apr 14 13:46:18 UTC 2005
18:22 12 April 2005
NewScientist.com news service
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Josef Kas, University of Leipzig
Institute of Physics, UK <http://www.iop.org/>
Optical trapping group, St Andrew's University
Sex and cloning, New Scientist <http://www.newscientist.com/channel/sex>
Measuring the "stretchiness" of cells using a new laser technique promises
to pinpoint human stem cells in blood and distinguish cancerous cells from
benign ones, say researchers.
Using an "optical stretcher", which pushes and pulls individual cells to
measure their elasticity, Josef Kas and Jochen Guck from the University of
Leipzig in Germany successfully separated adult stem cells from human
They say they can also pick out cancerous cells from biopsies as small as
just 50 cells - traditional methods need between 10,000 and 100,000 cells
to give a diagnosis. Furthermore, the researchers say this is the first
test able to identify metastatic cancer cells - those which are prone to
spreading through the body to form secondary tumours - without actually
locating any metastatic tumours.
"We have developed a very good way to recognise different cells based on
something known since the 1950s - that very different cells have very
different skeletons," says Kas.
He says the optical technique developed by the team is relatively simple
and low cost, yet could offer a highly specific way of identifying stem
cells, with the added benefit of a high throughput. "Sometimes the simple
ideas are the ones people overlook," he told New Scientist, adding that its
simplicity is the reason for its broad applications.
The new technique could lead to advances in medical treatments, says
Michael Watts, a haematology and stem cell expert at University College
London, UK. "We could significantly add to our knowledge of stem cell
biology, [aiding the search for] cellular therapies," he says.
"This is really an amazing technique," says Kishan Dholakia, professor of
physics at St Andrew's University, UK. He says it might allow diagnoses
from very small samples from patients in the future - reducing the need for
distressing or damaging tests.
Cells from most organisms have an internal scaffolding, called a
cytoskeleton, which keeps their shape and helps them move. But this
structure is less strong in cells which either have no reason to organise
themselves, like primitive stem cells, or because they "de-differentiate",
like cancer cells - which lose the special characteristics of the tissues
in which they originated.
This means that stem cells and cancerous cells
<http://www.newscientist.com/article.ns?id=mg17723863.100> are more springy
than other cells. And metastatic cells are suppler still.
Using the optical technique, cells from a sample are pushed one by one into
a gap between two opposing infrared lasers. As the light from each laser
beam enters the cell, it changes momentum because the cell has a higher
refractive index. This gives the cell a "kick back", explains Kas, and when
the beam leaves the cell it gives it a "kick forward".
The kicks in opposite directions stretch the cell, and the amount by which
the cell extends can be measured and used to identify it from a population
of cells. Two beams are needed to keep the cell in a stable configuration.
The technique differs from previous "optical tweezers" methods - which use
just one focused laser beam to hold a cell in place. However, this could
damage or alter the cell, and at higher intensities it could just "fry
everything", says Kas.
The optical stretcher can already test 3600 cells per minute. And as well
as being highly specific, it does not require the use of expensive chemical
markers currently needed to identify stem cells, he says.
"The real excellence is they have got a good flow rate and throughput,"
says Dholakia. They have overcome the technical difficulty of channelling
cells through the tiny space between two lasers, which he likens to trying
to individually catch and squeeze many footballs bobbing in a river.
The new technique is currently being used to separate stem cells to treat
elderly patients for persistent non-healing wounds and also at a heart
clinic in Leipzig where doctors plan to inject a patient's own stem cells
back into their heart muscle to aid recovery in the wake of a heart attack.
The device will also be trialled for screening cancers. Dentists in Leipzig
will take swabs from patients to test for oral cancer, which is normally
detected only when a tumour has developed, by which time the effects are
The work was presented by Kas at the Institute of Physics meeting in
Warwick, UK, on Tuesday.
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