Picking Out Parasites

Even in a fully equipped laboratory, diagnosing tropical diseases isn’t always easy. Blood parasites must be detected against a massive background of normal cells – a task to which complex microfluidic tools with pressure regulation, monitoring and microscopy are well-suited. Unfortunately, those tools aren’t usually available in the field, where blood parasite diagnosis is most needed but resources can be extremely limited. Jonas Tegenfeldt and his colleagues took on the challenge of finding a solution that works in all environments.

“A number of parasitic blood infections decimate populations in the developing world,” says Tegenfeldt. “Diagnosing these diseases remains problematic.” He and his team had been working on microfluidic cell sorting for many years when it occurred to them that differences in shape and motility would make the parasites amenable to separation from normal blood cells, and this separation could be achieved using a simple device. Tegenfeldt explains, “Three different separation schemes are combined into a single device. First, white blood cells are removed from the blood. Second, the remaining red blood cells and parasites are moved to the side to create an empty stream of plasma, into which the parasites are focused in the third step. Each step requires an optimized design for its particular task, which presented both a fabrication challenge – to accommodate different depths – and a fluidics challenge – to align the flow of the fluid so that the three different sections work well together.” The platform they devised is based on deterministic lateral displacement, deflecting particles in different directions based on size (1). It’s the size of a microscope slide, contains inexpensive materials, has no moving parts, and requires no power, making it an ideal solution for underprivileged areas.

It’s currently quite difficult to diagnose diseases like African trypanosomiasis because cases must be confirmed by positive identification of parasites in the blood – and they can be hard to find. “Some infections are at extremely low level,” Tegenfeldt warns. “There may be as few as 10 of these cells in one milliliter of blood, so it’s important to take sufficient volumes and to pre-enrich the parasites to get successful separations.” He and his group are currently working toward linking their device with a pre-enrichment step, in the hope that they can make diagnosis easier and enable faster treatment for patients with parasitic disease.