Raman microscopy could improve and simplify malaria diagnosis in remote locations, claim a team of scientists from Australia and Germany.

Malaria parasites are spread through mosquito bites

Malaria is one of the world's most devastating diseases. It kills more than a million people each year, mostly in Africa. Easy-to-use dipstick tests can rapidly detect malaria in blood but they do not reveal the number of malarial parasites, which scientists use to decide upon a treatment. Although some diagnostic tools can both identify and quantify the parasites, they are difficult to use.

Don McNaughton, at Monash University, Clayton, Australia, and colleagues have combined bright-field and dark-field microscopy with Raman spectroscopy to detect malarial parasites in blood. The method is as easy to use as a normal microscope, they say, and can be automated so the operator does not have to make the diagnosis.

Bright-field microscopy illuminates a sample and its surroundings from below. The surroundings appear bright while the sample appears dark. In dark-field microscopy, only the light scattered by the sample is seen through the lens, so the sample appears bright and the surroundings dark.

By combining these techniques, the team created a partial dark-field effect that lights up a malarial pigment called haemozoin, which they then detected by Raman spectroscopy. Malarial parasites are difficult to see by bright-field microscopy alone because cells may be overlaid and so obscured from the light, McNaughton explains.

'This combinatorial approach opens the way towards a new powerful malaria diagnostic tool in routine clinical practice,' says Juergen Popp, an expert in microscopy and biophotonics at Friedrich Schiller University of Jena, Germany.

The next step is to see if this new technique can differentiate between different stages of the parasite life cycle, remarks NcNaughton. 'We hope to achieve this by correlating the Raman spectral images with stained sections [from conventional diagnostic techniques] and determining spectral markers for each stage of the life cycle.'

Rebecca Brodie

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