How easy is it to diagnose malaria? Professor Dave Newman of the University of Exeter in England has created a portable magneto-optical instrument to do the job in a minute. And, when his new method is fully refined, it may not even need a blood sample.
Newman’s expertise as a physicist involves materials for magneto-optical recordable discs. Used since the late Eighties, these rely on measuring a change in laser light reflected from magnetic media in different magnetic states.
There’s also a link between malaria, magnetism and light. Red blood cells are infected by the malarial parasite (plasmodium) from female Anopheles mosquitoes. The oxygen-carrying haemoglobin is digested by the parasite, forming haemozoin which exhibits properties that are attracted to magnetic fields.
Some years ago, Newman considered researching malaria diagnosis, but was prevented by blood safety restrictions. Then he moved to the University of Exeter. “I went back to this idea and, by talking to a biologist friend of mine, I came to the conclusion that maybe it was possible to detect malaria by detecting the haemozoin by magneto-optics.”
Thanks to European Union funding, Newman and colleagues from Exeter and Coventry universities have now tested a prototype instrument at the Royal Tropical Institute in Amsterdam. Clinical trials are also planned in Kenya.
It works like this. The parasite produces haemozoin in the form of rectangular rod-like crystals and, normally, the long axes point in random directions. “When you apply a [magnetic] field to them, they become magnetised and all orient in the field direction,” says Newman.
The crystals also absorb polarised red laser light more strongly along their length than the width (optical dichroism). Put a blood sample into the instrument, apply a directional magnetic field, then a laser and photodetector take optical measurements proportional to the haemozoin concentration. “The intention is to produce something about the size of a shoe box which will be rugged enough to go out into the field,” says Newman.
Colin Sutherland is a senior lecturer at the London School of Tropical Medicine and Hygiene and a clinical scientist at the Hospital for Tropical Diseases. He says malaria is usually identified with a microscope or by antigen diagnostic kits which might not be too reliable. “This particular test looks very exciting,” he says. “The fact that it’s rapid is great, but it will, of course, need to be emphasised that for a test to be usable by a malaria control programme in Africa, it must be affordable and portable.”
Newman is researching a prototype that doesn’t use a blood sample. Instead, he envisages putting a finger inside a box within a magnetic field, shining a laser beam on to a fingernail and taking an optical reading from the blood beneath. —