Pseudo-Infected Red Blood Cell Beads as Positive Control for Cell Microarray Chip–Based Detection of Plasmodium-Infected RBCs

The cell microarray chip is a polystyrene plate with 20,944 microchambers, and it is used to detect red blood cells (RBCs) infected with the causative agent of malaria, Plasmodium. Plasmodium-infected red blood cells (iRBCs) stained with a nuclear staining dye (SYTO 21) form a monolayer on the bottom of the microchambers, and about 130 RBCs are accommodated in each such microchamber of the chip. The iRBCs in the RBC monolayer (containing 2.7 million RBCs) can be identified using a fluorescence detector, and the infection rate can be calculated by counting the number of fluorescent-positive RBCs. This diagnostic device is highly sensitive and hence advantageous for early diagnosis of malaria infections in endemic areas. However, a standard positive control for Plasmodium-infected RBCs is required to ensure that the reagents and detectors of these cell microarray chips are working efficiently in remote endemic areas. Here, we introduce “pseudo-iRBC beads,” which consist of a mixture of DEA beads mimicking RBCs and DEA beads coated with nucleic acids mimicking nuclei of the parasite. These beads can be stained with SYTO 21, applied onto the cell microarray chip to form a monolayer, and detected using the fluorescence detector in the same way as iRBCs. Therefore, the introduction of pseudo-iRBC beads as a positive control ensures unbiased malaria diagnoses with the cell microarray chip device in remote endemic areas.