Spotlight on Research is the research blog I author for Hokkaido University, highlighting different topics being studied at the University each month. These posts are published on the Hokkaido University website.
“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.