A model betalainic dye was semisynthesized from betanin, the magenta pigment of 
the red beet, and was effective for live-cell imaging of Plasmodium-infected red 
blood cells. This water-soluble fluorescent probe is photostable, excitable in 
the visible region and cell membrane-permeable, and its photophysical properties 
are not notably pH-sensitive. Fluorescence imaging microscopy of erythrocytes 
infected with Plasmodium falciparum, a causative agent of malaria in humans, 
showed that only the parasite was stained. Z-stacking analysis suggested that 
the probe accumulates proximal to the nucleus of the parasite. Indicaxanthin, 
one of the natural fluorescent betalains found in the petals of certain flowers, 
did not stain the parasite or the red blood cell.