Lynn Paterson’s group at the Institute of
Biological Chemistry, Biophysics and Bioengineering
at the Heriot Watt University, Edinburgh,
UK, found ways to isolate microbes
using the force of light. Paterson is associated
with the MaCuMBA work package
‘Development of hardware and equipment
for high throughput isolation, cultivation
and screening’. “We have developed optical
tweezers and an optofluidic device, which
we will be exhibiting at the final MaCuMBA
conference in Berlin. Feedback from the attending
scientists will be useful, to determine
whether there is a market for our laser
tweezers, or whether the community will be
better served by offering a cell isolation service,”
the molecular biologist and Lecturer
in Physics said. The optofluidic device is still
at the research stage.
Pulling...
The acting force behind the optical
tweezers is a laser beam that is tightly focussed
through a microscopic objective.
The optical force pulls a nearby cell into
the beam focus and traps it, so that it can
be moved in three dimensions. The scientists
chose near infrared laser light to minimise
damage to the cells, which can occur
by heating the cells or via the generation
of free radicals. “We’ve fabricated bespoke
microscope slides with reservoirs, channels
and collection chambers, in which to collect
and culture individual cells. Supported by
our project partners, we have also developed
software to make the process more user-
friendly and semi-automated,” Paterson
reported. Using laser tweezers, the scientists
could isolate a wide range of lab-grown
bacteria as well as microalgae and yeast.
...and pushing under the microscope
The novel optofluidic device makes
use of the scattering force of light. Even
when not tightly focussed, laser light can
exert a force on particles and make them
move by pushing them in the direction of
beam propagation. “Much like a football
can be pushed in a jet of water from a fireman’s
hose,” Paterson said by way of illustration.
The researchers also prepared bespoke
three-dimensional microfluidic circuitry
with integrated waveguides to control
the flow of cells in a sample. For this,
they used ultrafast laser inscription and selective
chemical etching, a technology developed
by Ajoy Kar at Heriot Watt University.
“This means we can direct light into the
microfluidic
channel and, using the scattering
force, push selected cells out of the
stream in order to isolate them. You can
call it ‘flow cytometry and flow sorting on
a chip’,” Paterson explained. The small device
has dimensions of 2x3x1 mm. The researchers
were able to manipulate microalgae
two micrometres in diameter and larger
cells, such as mammalian cells. The device
still has to be optimised for the sorting
of bacteria.
Moreover, scientists associated with
the Université de Bretagne Occidentale developed
the ‘Cocagne platform’. “With this
high-throughput system, we can simultaneously
culture hundreds of aero-tolerant,
non-pathogenic microorganisms in different
media and at different temperatures,
isolate and identify strains, and screen for
substrate degrading or antimicrobial activities,”
said Gwenaelle Le Blay, leader of the
work package ‘Improving culture efficiency
of already isolated and cultured microorganisms’.