Taking pictures with a time machine

Dr Daniel Davis, Dr Ilya Eigenbrot, Dr Dan Elson, Professor Paul French, Dr John Lever, Dr Mark Neil, Professor David Phillips OBE, Professor Gordon Stamp and Dr Klaus Suhling.
Imperial College London.

Being able to watch molecules at work inside living tissue without damaging or disturbing it is a 'holy grail' for life scientists and clinicians. Now, a team of physical and life scientists, engineers and medics at Imperial College London is making this a reality. They are developing a way of using ultrafast lasers to observe the behaviour of proteins and other molecules in living tissue. As well as seeding a revolution in basic research, the technology could also help diagnose diseases such as cancer and arthritis, even before a patient experiences symptoms. 'The potential is enormous and very exciting,' says Professor Paul French, who heads the team.

Until now, most researchers have relied on special dye stains or antibodies to reveal the position of specific types of molecules under study in cells and tissue samples. The trouble is, most of these methods kill the sample being studied. There are some methods that let you use living samples but so far these yield only limited information about molecular interactions.

The technology being developed by the Imperial team addresses these issues, extending established techniques of fluorescence imaging to the time domain. This relies on the observation that many molecules will 'glow' in a characteristic way when you shine a laser on them. The colour and the brightness of the glow can give a lot of information about the molecule, but they are not always specific enough to identify it.

Recently scientists have started looking at the temporal aspect of the glow- its lifetime, or how long the glow lasts after the laser stops shining. Add this lifetime information on to the colour and brightness information and you can get a unique multi-dimensional 'fingerprint' for identifying a particular molecule. What's more, the glow's lifetime will be affected by the molecule's environment, so you can deduce what a molecule's surrounding is like and whether it is interacting with other molecules. This means that, as well as being able to identify different molecules, Fluorescence Lifetime Imaging (or FLIM) can provide insight into how molecules function.

The Imperial team is developing ways of applying FLIM in biological research and medicine. By coupling lasers to microscopes, they are using FLIM to watch living cells.

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