Selection and Characterization of Aptamers for the Development of a Point-of-Care Malaria Diagnostic Device

Malaria is a life-threatening disease caused by several species of Plasmodium parasite. Rapid tests (RDT) exist for malaria diagnosis that employ antibodies for detection of Plasmodium antigens in patient blood. However, antibodies are an expensive biocomponent of limited shelf-life. As an alternative, aptamers are short oligonucleotide sequences, selected and produced in vitro, that selectively bind to specific targets in a similar fashion to monoclonal antibodies. We selected Plasmodium falciparum lactate dehydrogenase (Pf-LDH) specific ssDNA aptamers using a protein-SELEX assay. K_d values and cross-reactivity with Plasmodium ovale, Plasmodium vivax, and Plasmodidum malariae LDHs were determined by ELONA. The best-performing aptamers showed nanomolar binding affinity towards Pf-LDH., with different levels of crossreactivity to P. ovale and P. malariae LDHs. They were stable in 100% human serum for up to 3 h and in 10% human serum for up to 24 h. One of the selected aptamers was successfully implemented as the detection receptor in a rapid electrochemical magneto biosensor. This provided Pf-LDH quantitation in less than 15 min, with a limit of detection of 1.,0ng-ml.' and little handling for the user. These results show that customized aptamers could serve as sensitive and selective synthetic receptors to develop costeffective point-of-care biosensors for malaria diagnosis.