HEALTH
Why scientists are making
human cells emit laser beams
10 September 2015
by Jon Cartwright
Illuminating cells lets researchers track them easily. Image courtesy of Matjaž Humar and Seok-Hyun Yun
Scientists have been able to engineer human cells to emit a unique laser 'barcode', a
breakthrough that could help to track the spread of cancer cells throughout the body.
The short history of cell lasers goes back to 2011, when physicists Dr Malte Gather and Professor
Seok-Hyun Yun of Harvard Medical School, US, engineered human cells to make them express a
fluorescent protein, and placed them between a pair of tiny mirrors.
When the scientists pumped the cells with a blue laser, the cells re-emitted the light as green. This light
reflected back and forth between the mirrors to form a coherent beam, just like a normal laser.
However, those cell lasers had limited application, given that they needed external mirrors to function.
The trick has been to find a way of getting a pair of mirrors, or some other resonant cavity, inside the
cells themselves.
Physicist Dr Matjaž Humar was awarded an EU grant to work with Prof. Yun at Harvard Medical School
to solve this problem. His answer has been to inject cells with droplets of oil dyed with a fluorescent
compound which act as resonant cavities to reflect the light.
This is the same phenomenon that underlies the
hemispherical ‘whispering galleries’ sometimes
seen in cathedrals, libraries and other old buildings,
in which a whisper can be heard far away by
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echoing around the gallery’s circumference.
Because of the droplets’ spherical shape, any light
generated by the fluorescent dye likewise resonates
around, ultimately generating a coherent laser
beam.
With this current technology, it is thought a few
thousand cells can be fashioned into lasers and
barcoded. But the researchers believe that as the
cell lasers get more complex, the number of
individual barcodes could go into the hundreds of
thousands or more – far exceeding any current
method of medical tagging.
‘You could almost
tag the total number
of cells in the human
body.’
Dr Matjaž Humar, Harvard
Medical School, US
‘You could almost reach the total number of cells in the human body,’ said Dr Humar. ‘In principle, there
could be that many combinations.’
Dr Humar and Prof. Yun are not the only ones to have made standalone cell lasers. Backed by a grant
from the EU's European Research Council, and now a professor at the University of St Andrews in the
UK, Prof. Yun’s previous colleague Prof. Gather has worked with others to make cells ‘eat up’ microbeads, rather than oil droplets, by a natural process called endocytosis.
Unique colour
Like the oil droplets, the micro-beads resonate inside the cells to generate laser light. But the real boon
with both groups’ cell lasers is the unique colour of their light – unique like a barcode – which is
provided by subtle variations in the size of the beads or droplets.
The researchers say that, in theory, certain cells could be made into lasers inside the human body. A
while later, a scientist armed with a spectrometer – a device that can discern subtly different colours of
light – could scan the human subject to find out where the cells had gone.
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Dr Gather believes this could help biologists understand the spread of tumours to different parts of the
body. Such metastasis is believed to occur when tumour cells break away from the main tumour, but
no-one is clear what subsequently happens to them.
‘The only way you could find out would be to track every cell that detaches from the tumour,’ said Dr
Gather. This, he adds, might become possible with cell barcoding.
Other biological processes, such as immune response and morphogenesis – that is, how an organism
develops its shape – could also be investigated with the cell lasers, he says.
Dr Gather and his colleagues have already got several different types of cell to take up the micro-beads
to form lasers. The next step will be to make the micro-beads compatible with all cells, so that the
barcoding technique is universal.
‘Provided we can confirm the technique is generally applicable, I believe cell laser-based barcoding has
a very good chance of becoming a new standard method in in-vivo microscopy,’ said Prof. Gather. ‘We
are keen to now explore in detail how it performs in complex biological environments.’
More info
Dr Malte Gather
Dr Matjaž Humar
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