In SPIN
Ireland's science wildlife and discovery magazine
Archive
Science Spin September 2007
Dread the needle?
Relief is at hand for those petrified of needles
The moment arrives. You are with your GP and you have a nagging feeling he's going to mention the N word. And, sure enough, as he says, "I think we'll run some blood tests", with the nonchalance of those who don't dread the Needle, you begin to think you'd rather live with whatever disease is causing your symptoms, nasty as it may be.
[Picture Credit: Washington State University]
If you're a fully paid up member of the needle-phobic club, then kick back and imagine a future of blood tests minus the needles. And while you're at it, imagine the same technique being sent to Mars to analyse rock composition or to probe the secrets of the Mona Lisa. Finding it hard to imagine all this? Allow me to introduce the Raman effect, a quirk of light that's responsible for making all of the above a reality.
Technology
Raman spectroscopy uses the "bouncing" properties of light when it's shone onto a substance. Light occurs in different wavelengths -- we see these as colours -- or colours and usually they occur as a mix. Light of a single wavelength is called monochromatic light and can be produced in very high intensity by a laser.
When photons of monochromatic light are shone onto a substance, most of the photons bounce off and are reflected in the exact same wavelength as the light from the laser; this is called Rayleigh scattering and for every 10 million photons of light shone onto your substance this will happen 9,999,999 times. Of course it's Murphy's law that the really interesting part -- the Raman scattering -- and this happens only once every 10 million times.
These errant photons interact and exchange energy with the test substance and are reflected in a different wavelength than the light from the laser. Capture and analyse these photons making up the Raman scattering and you get a spectrum unique to that particular substance -- the chemical equivalent of a fingerprint. Unfortunately for beleaguered scientists everywhere, life (and science) is never that easy.
Imagine being on a gameshow; to win the jackpot you have to find the one green jellybean hidden in a box of 9,999,999 red jellybeans and if that wasn't hard enough you're working against the clock with a grand total of 10-14 seconds to find it before all the jellybeans disappear along with your jackpot. This was the challenge facing Sir C V Raman in 1930 when he won the Nobel prize for his observations of Raman scattering.
Until the last two decades, widespread application of Raman spectroscopy was limited by the instrumentation available but technology has finally caught up and has allowed researchers to start exploiting Raman spectroscopy for a truly phenomenal range of tasks.
Application
One application of Raman spectroscopy is blood testing without the needle -- something that Ireland's 200,000 diabetes sufferers will be glad to hear, given that they need to check their blood glucose levels several times a day. Imagine you're back in the doctor's surgery, and this time when he suggests blood tests, you don't break out in a cold sweat because all he's only going to shine a light on your finger.
This technology is still in the early stages and there are many problems to overcome, not least the fact that human skin and blood are composed of literally thousands of substances that all produce Raman spectra of their own, masking the one spectrum you're looking for.
It would be like a thousand people all signing on the dotted line and then trying to distinguish your own signature from all the others. The way around this is to compile a database of spectra from substances that you would expect to find in the skin and blood. Powerful software can then recognise and subtract these spectra until the jumble has been cleared up. and the spectrum of interest is the only one left.
Scientists in MIT, Cambridge, USA, have successfully used Raman spectroscopy to measure glucose in the blood by shining light on the skin and their results correlated with standard glucose testing made via the more traditional needle. Eventually this technique could be used to measure any number of blood analytes, including cholesterol.
Unfortunately needles are unlikely to be completely banished from the clinic but Raman spectroscopy gives a glimmer of hope that routine blood analysis could soon be performed without scaring the pants off a significant proportion of the population!
