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Fingerprinting meningitis with lasers

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Media captionThe scientists are using lasers and nanoparticles to test samples

Every case of bacterial meningitis is an emergency.

It may not be as common as the viral type but without swift treatment the inflammation of the tissues surrounding the brain and spinal column can lead to blood poisoning, brain damage, even death.

It is most common in children under five. And that throws up a whole new set of problems for doctors trying to establish precisely which bacteria are behind it.

Dr Karen Faulds, a reader in the department of pure and applied chemistry at Strathclyde University, explains: "They'll use a broad-spectrum antibiotic because they won't know what is actually causing the infection at that point."

But broad-spectrum treatments can attack not just harmful bacteria in the body but beneficial ones as well. They also contribute to the rise of antibiotic-resistant strains.

"They would take a lumbar puncture," say Dr Faulds, "which is painful.

Image copyright Spl
Image caption Bacterial meningitis is most common in children under the age of five

"Also if you're taking it from children or babies the amount of sample you can collect is going to be very small.

"And obviously you don't want to go back and take another lumbar puncture. You want to get it right first time and get the information that you want - that you need."

So small sample sizes and perhaps more than one bacterium causing the illness: a conundrum that Dr Faulds and her team are solving with nanoparticles, lasers and computer power.

First a small sample of spinal fluid is amplified using a "fast-ramp" process to amplify the bacterial DNA.

Then the new process takes over. It is called Surface Enhanced Raman Scattering (SERS).

A laser beam is fired at the sample and the scattered light analysed. The enhancing takes place because the sample has been mixed with silver nanoparticles. They increase the signal and make the test much more sensitive.

"Essentially what you do is shine a laser beam at the molecule and measure the shift in wavelength," says Dr Faulds.

"This gives you a fingerprint - what you call a vibrational spectrum.

"And you can definitively identify that molecule."

Image caption The test can detect more than one disease-causing agent at once.

But SERS offers a lot more. Because it can detect more than one disease-causing agent at once.

In the laboratory, doctoral student Kirsten Gracie shows me how.

"So that's the sample prepared," she says.

"We then place it in the spectrometer and just turn on the laser beam.

"You can see that the laser is hitting the sample directly - you can see that nice scattering."

It's impressive, but what appears on the computer monitor is even more so: a graph with three distinct peaks representing three different types of bacteria. It would mean doctors could target each of the bacterial pathogens accurately.

Dr Faulds, working with colleagues at Manchester university, has used SERS not just to identify different bacteria, but quantify how much of each pathogen is present.

Image caption Dr Karen Faulds is part of the team that has developed the test

"This is the first time we've managed to do this," she says.

The SERS test, details of which have been published in the journal Chemical Science, holds out the prospect of speedy and efficient treatment of bacterial meningitis.

But its potential is far greater.

The Strathclyde researchers are confident the technique can be refined even further. More sensitivity would mean even smaller sample sizes, so the DNA amplification stage could be bypassed to offer even faster diagnosis.

And they say SERS could be applied to any kind of pathogen that contains DNA such as fungi or viruses.

And while it's likely a meningitis diagnosis would still need a sample of spinal fluid, other diseases in other parts of the body could be identified using other, less painfully gathered, fluids such as blood, urine, or even tears.

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