Diagnosing malaria using light and sound

Malaria infects more than 200 million people each year, almost all of them in the developing world. The disease, once diagnosed, is readily treated in most cases. But malaria can be difficult to distinguish from other illnesses based on symptoms alone, and current diagnostic methods require trained medical professionals or specialized reagents. Now Dmitri Lapotko, Ekaterina Lukianova-Hleb, John Olson, and their colleagues at Rice University and the Johns Hopkins Bloomberg School of Public Health have devised a technique with the potential to diagnose malaria quickly and cheaply. When the single-celled malaria parasite infects some of the host’s red blood cells, it digests hemoglobin to produce a substance called hemozoin, which accumulates as crystals 50–400 nm in diameter. In experiments in vitro and on mice, the researchers discovered that when the hemozoin nanocrystals are excited by a picosecond 672-nm laser pulse, they absorb enough energy to vaporize a small volume of the surrounding fluid. The vapor nanobubbles’ expansion and collapse generate a detectable acoustic pulse. Both the laser pulse and the acoustic signal can pass through the skin, so the diagnosis can be performed without drawing blood. The researchers have shown that the technique does no damage to uninfected blood cells or other tissues, and they are presently conducting their first study on human patients. (E. Y. Lukianova-Hleb et al., Proc. Natl. Acad. Sci. USA 111, 900, 2014, doi:10.1073/pnas.1316253111 .)