Thiazole orange: A new dye forPlasmodium species analysis

Abstract

A rapid sensitive method for the determination of Plasmodium falciparum in in vitro culture is presented. The technique employs a fluorescent flow cytometer equipped with a 15‐mwatt argon laser that emits light at 488 nm and a membrane‐permeable fluorochrome thiazole orange (TO) that stains RNA. Parasitized red cells are stained by suspending them in 1 ml of phosphate‐buffered saline (PBS) containing 10^×5 M of TO and incubating this mixture for 15 min in the dark at room temperature. The stained cells may be analyzed fresh or after fixation with 1% paraformaldehyde/PBS or 0.25% glutaraldehyde/PBS. Alternatively the cells may be fixed first and then stained. There is excellent correspondence between the number of fluorescent‐labeled parasitized red cells and Giemsa‐stained cells.