Proc. Natl Acad. Sci. USA http://doi.org/q5n (2014)

At present, malaria is diagnosed using techniques that rely on invasive blood sampling, specific reagents and expert knowledge. Dmitri Lapotko and colleagues at Rice University and the John Hopkins Bloomberg School of Public Health have now developed a non-invasive, reagent-free method to diagnose the disease, which uses a laser to generate nanoscale vapour bubbles within malaria parasites in a patient's body and then detects the subsequent collapse of the bubbles.

Malaria parasites in the blood are known to digest haemoglobin from red blood cells and form nanoparticles called hemozoin. Vapour bubbles as small as 100 nm can be generated from hemozoin by using a near-infrared laser pulse. The heat from the laser rapidly expands the volume of the bubble until it 'pops', generating a signal for acoustic and optical detection. Using infected human blood samples, the researchers were able to distinguish between early- and mature-stage parasites based on the traces generated by the nanobubbles. They were also able to detect the subsequent destruction of the hemozoin-containing blood cell; healthy blood cells were unaffected.

Lapotko and colleagues also showed that infection levels as small as 0.00034% could be detected in malaria-infected mice by placing a laser probe against their ears and delivering 400 laser pulses in 20 seconds and then detecting the acoustic response.