Life under the microscope
When you mention lasers, many people still think of death rays, but the new generation of laser-based multiphoton microscopes are shining light on all sorts of medical problems, from cancer to toothache. In the early 1990s, biologists used microscopes to study different embryos by staining them with chemicals called fluorophores, then shining a very bright light on the cells…
This worked very well but in the process, the embryos died. Today, the same biologists can track the life of animals like hamsters from the time they are only a small bunch of cells until they’re old enough to go for a spin in their wheels, without doing any damage at all.
The key advantage of this new technique – apart from not killing the hamster before it is born – is that biologists can study the same embryo at every stage of its development, rather than studying different hamster embryos at different stages. If testing the effects of pharmaceuticals, for example, this means the results are more consistent throughout the experiment – and therefore more reliable as well as faster and more economical.
The story starts when Professor Allister Ferguson of the physics department at the University of Strathclyde in Glasgow was asked by a biologist called John White, then working in Cambridge, what he knew about something called ‘confocal microscopy’. After ‘bluffing’ for several minutes, as Ferguson recalls his reaction, he asked White to explain what ‘confocal microscopy’ was, and in the process learned about the problems of in vivo imaging (studying living organisms under the microscope) – using the available technology.
White had contacted Ferguson after he read of his work in developing ultrashort pulse lasers to study atomic hydrogen, thinking this may be the answer to the problem of killing the cells. Another problem for White was that using fluorophores and other indicators to ‘mark’ living cells sometimes bleached the samples, making them impossible to see. Several other academics and commercial developers told White he was wasting his time in his search for a compact laser-based system, but Ferguson immediately saw that his work with ‘2-photon microscopy’ could provide what White needed.
“Too much light cooked the subjects or created toxic products, but I knew ultrashort pulse lasers could be the answer,” says Ferguson. “The objective was to make a multiphoton system compact and easy to use, so that biologists and other scientists without a physics background could use them just like any other microscope.”
Lasers for multiphoton microscopes at that time were as big as a room, but Ferguson believed that it was possible to develop a solid-state version, taking advantage of recent developments in semi-conductors to miniaturise the components and pack in more intelligence, using tiny, tightly focused lasers with extremely short light pulses (10-13 second) to illuminate the specimens safely, then use raster-scanning (a data mapping mechanism) to build up an image for viewing.
Ferguson’s experience with White gave him an appetite for working with biologists, and he later went on to develop his prototype system and founded a company called Microlase Optical Systems to manufacture lasers for multiphoton microscopes. After selling Microlase to Coherent Inc. of the US, Ferguson continued to develop his research interests in the area and moved on to establish the Centre for Biophotonics in Glasgow, which brings together life scientists and physical scientists and provides an opportunity for Ferguson to mentor the new generation of researchers.
Ferguson strongly believes that his work in pure physics was what made it possible to develop the new kind of microscope, now widely used by biologists all round the world. “That is why it’s so important to have people study fundamental science – for example, using our knowledge of physics to solve biological problems,” he says. “After all, many esoteric scientific concepts eventually find their way into our everyday lives.”
Now ‘back where he belongs’ in the research lab, Ferguson is helping to push lasers further, and use them for new applications. One of the exciting new technologies being developed at the Centre for Biophotonics is something called CARS (Coherent Anti-Stokes Raman Scattering) microscopy, a non-invasive, label-free, highresolution form of three-dimensional microscopy.
New laser-based technologies like CARS can be used for a wide range of tasks – including immunology and ophthalmology, as well as embryology, brain imaging, electrophysiology, cancer diagnosis, pharmaceutical development and even the prevention of tooth decay.
Using MPM, researchers can study the effects of a new drug on one single cell, and pass or reject it without needing to test it on humans. Because of the ability to scan to greater depths, dentists in the future will be able to use handheld scanners to reveal the early signs of tooth decay and stop it becoming a problem. Another benefit is chemical specificity – the ability to tune lasers so they can detect specific chemicals.
With adaptive optics, using special mirrors to adjust focal range, imaging quality takes yet another step forward. “The progress is spectacular,” says Ferguson. “We’ve gone from the outer limits of science to something that researchers can aspire to in their everyday work.”