You might be familiar with the use of CT and MRI scanners in hospitals to allow doctors to “see” inside the human body. This is very helpful detecting diseases such as cancer since the doctor can see where the tumours are. We cannot directly see the X-Rays and radio waves these instruments use to look through tissues and organs within the body and we need computers to create an image we can see.
Visible light, like X-Rays and radio waves, can also travel through tissue and unlike X-Rays you can actually see it. Try holding your finger or hand up against a torch and the light passing through your skin makes the edges of your finger take on a reddish glow. Unlike X-rays, visible light doesn’t travel through the body very well – it’s readily scattered or absorbed, and only the red part of the visible spectrum is able to pass through. In some respects it’s just as well, otherwise we’d be able to see right through everyone we met and see all their insides!
However there are molecules that can emit light we can see, through a process called fluorescence. We can use these molecules as tags or labels (like a flare or a beacon) to light up and show where a tumour might be growing. Fluorescent tags aren’t limited to lighting up cancerous cells. We can use light emitting molecules to help us detect the onset of any sort of illness, if we know the target we are trying to hit with it.
Visible light is versatile since we can use it in different ways – we can measure the time it takes to pass through different tissues and so build up a picture. Even more simply, we can use visible light of different colours to label different tissues under different conditions, to provide an accurate picture of what might be happening inside us. It’s almost like dying your clothes to make you stand out from the crowd.
The Nobel Prize for Chemistry this year was shared by three scientists who discovered a natural fluorescent molecule called green fluorescent protein. It quite literally blazed a trail for using light to highlight what is going on inside living cells.
One of the winners no longer practices science. It just goes to show, like a beacon, a scientist’s work might shine briefly but it shows the way for the future researchers to follow.
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