Droplet Microfluidics Platform for Highly Sensitive and Quantitative Detection of Malaria-Causing <i>Plasmodium</i> Parasites Based on Enzyme Activity Measurement

We present an attractive new system for the specific and sensitive detection of the malaria-causing <i>Plasmodium</i> parasites. The system relies on isothermal conversion of single DNA cleavage–ligation events catalyzed specifically by the <i>Plasmodium</i> enzyme topoisomerase I to micrometer-sized products detectable at the single-molecule level. Combined with a droplet microfluidics lab-on-a-chip platform, this design allowed for sensitive, specific, and quantitative detection of all human-malaria-causing <i>Plasmodium</i> species in single drops of unprocessed blood with a detection limit of less than one parasite/μL. Moreover, the setup allowed for detection of <i>Plasmodium</i> parasites in noninvasive saliva samples from infected patients. During recent years malaria transmission has declined worldwide, and with this the number of patients with low-parasite density has increased. Consequently, the need for accurate detection of even a few parasites is becoming increasingly important for the continued combat against the disease. We believe that the presented droplet microfluidics platform, which has a high potential for adaptation to point-of-care setups suitable for low-resource settings, may contribute significantly to meet this demand. Moreover, potential future adaptation of the presented setup for the detection of other microorganisms may form the basis for the development of a more generic platform for diagnosis, fresh water or food quality control, or other purposes within applied or basic science.