Validation of PCQD as a tool for P. falciparum drug discovery. (A) Comparison of QD detection of increasing P. falciparum parasitaemia assessed by flow cytometry and manually from Giemsa-stained culture smears. The late-stage P. falciparum culture was serially diluted and incubated with PCQD and Hoechst and analyzed by flow cytometry. The plot shows the correlation (R2 = 0.9152) of the parasitaemia values detected by both methods. (B) Comparison of chloroquine DRCs using PCQD and pLDH assays. Synchronized young parasites were incubated with increasing concentrations of chloroquine. After 60 h of incubation, samples were either fixed and labelled with PCQD and Hoechst for PCQD assay or developed for the pLDH assay as described above. The plot shows a consistent EC50 of 26 nM for both assays. (C) The chloroquine DRC of a 24-h drug exposure within a single erythrocytic cycle using the PCQD assay. The DRC-derived EC50 was 113 nM.