Hokkaido University. Japan: “Everyone wants to see things smaller, faster, for longer and on a bigger scale!” Professor Bi-Chang Chen exclaims. It sounds like an impossible demand, but Bi-Chang may have just the tool for the job.
Professor Bi-Chang Chen and his colleague, Professor Peilin Chen, are
from Taiwan’s Academia Sinica. Their visit to Hokudai this month was
part of a collaboration with Professors Tomomi Nemoto and Tamiki
Komatsuzaki in the Research Institute for Electronic Science. The
excitement is Bi-Chang’s microscope design: a revolutionary technique
that can take images so fast and so gently, it can be used to study
living cells.
The building blocks of all living plants and animals are their
biological cells. However, many aspects of how these essential
life-units work remains a mystery, since we have never been able to
follow individual cells as they evolve.
The problem is that cells are changing all the time. Like
photographing a fast moving runner, an image of a living cell must be
taken very quickly or it will blur. However, while a photographer would
use a camera flash to capture a runner, increasing the intensity of
light on the cells knocks them dead.
Bi-Chang’s microscope avoids these problems. The first fix is to
reduce unnecessary light on the parts of the cell not being imaged. When
you look down a traditional microscope, the lens is adjusted to focus
at a given distance, allowing you to see different depths in the cell
clearly. A beam of light then travels through the lens parallel to your
eye and illuminates the sample. The problem with this system is that if
you are focusing on the middle of a cell, the front and back of the cell
also get illuminated. This both increases the blur in the image and
also drenches those extra parts of the cell in damaging light. With
Bi-Chang’s microscope, the light is sent at right-angles to your eye,
illuminating only the layer of the cell at the depth where your
microscope has focused.
This is clever, but it is not enough for the resolution Bi-Chang had
in mind. The shape of a normal light beam is known as a ‘Gaussian beam’
and is actually too fat to see inside a cell. It is like trying to
discover the shape of peanuts by poking in the bag with a hockey stick.
Bi-Chang therefore changed the shape of the light so it became a ‘Bessel
beam’. A cross-section of a Bessel beam looks like a bullseye dart
board: it has a narrow bright centre surrounded by dimmer rings. The
central region is like a thin chopstick and perfect for probing the
inside of a cell, but the outer rings still swamp the cell with extra
light.
Bi-Chang fixed this by using not one Bessel beam, but around a
hundred. Where the beams overlap, the resultant light is found by adding
the beams together. Since light is a wave with peaks and troughs,
Bi-Chang was able to arrange the beams so the outer rings cancelled one
another, a process familiar to physics students as ‘destructive
interference’. This left only the central part of the beams which could
combine to illuminate a thin layer of the cell at the focal depth of the
microscope.
Not only does this produce a sharp image with minimal unnecessary
light damage, but the combination of many beams allows a wide region of
the sample to be imaged at one time. A traditional microscope must move
point-by-point over the sample, taking images that will all be at
slightly different times. Bi-Chang’s technique can take a snap-shot at
one time of a plane covering a much wider area.
To his surprise, Bi-Chang also found that this lattice of light beams
(known as a lattice light sheet microscope) made his cells healthier.
In splitting the light into multiple beams, the intensity of the light
in each region was reduced, causing less damage to the cells.
The net result is a microscope that can look inside the cells and
leave them unharmed, allowing the microscope to take repeated images of
the cell changing and dividing. By rapidly imaging each layer, a three
dimensional view of the cell can be put together. Such a dynamical view
of a living cell has never been achieved before, and opens the door to a
far more detailed study of the fundamental working of cells.
Applications include understanding the triggering of cell divisions in
cancers, how cells react to external senses and message passing in the
brain.
“We don’t know how powerful this technique is yet,” explains Peilin Chen. “We don’t know how far we can go.”
This is a question Tomomi Nemoto’s group are eager to help with. In
collaboration with Hokudai, Bi-Chang and Peilin want to see if they can
scale up their current view of a few cells to a larger system.
“We’d like to extend the field of view and if possible, look at a
mouse brain and the neuron activity,” Bi-Chang explains. “That is our
next goal!”
It is an exciting possibility and one that may be supported by a new
grant Hokudai has received from the Japanese Government. Last summer,
Hokudai became part of the ‘Top Global University Project’, with a ten
year annual grant to increase internationalisation at the university.
Part of this budget will be used in research collaborations to allow
ideas such as Bi-Chang’s microscope to be combined with projects that
can put this new technology to use. Students at Hokudai will also get
the opportunity to take courses offered by guest lecturers from around
the world. These are connections that will make 2015 the best year yet
for research.