Abstract
BackgroundMalaria infects over 300 million people every year and one of the major obstacles for the eradication of the disease is parasite's resistance to current chemotherapy, thus new drugs are urgently needed. Quantum dot (QD) is a fluorescent nanocrystal that has been in the spotlight as a robust tool for visualization of live cell processes in real time. Here, a simple and efficient method using QD to directly label Plasmodium falciparum-infected erythrocytes (iRBCs) was searched in order to use the QD as a probe in an anti-malarial drug-screening assay.MethodsA range of QDs with different chemical coatings were tested for their ability to specifically bind iRBCs by immunofluorescence assay (IFA). One QD was selected and used to detect parasite growth and drug sensitivity by flow cytometry.ResultsPEGylated-cationic QD (PCQD) was found to specifically label infected erythrocytes preferentially with late stage parasites. The detection of QD-labelled infected erythrocytes by flow cytometry was sensitive enough to monitor chloroquine anti-malarial toxicity with a drug incubation period as short as 24 h (EC50 = 113nM). A comparison of our assay with another widely used anti-malarial drug screening assay, the pLDH assay, showed that PCQD-based assay had 50% improved sensitivity in detecting drug efficacy within a parasite life cycle. An excellent Z-factor of 0.8 shows that the QD assay is suitable for high-throughput screening.ConclusionsThis new assay can offer a rapid and robust platform to screen novel classes of anti-malarial drugs.
Highlights
Malaria infects over 300 million people every year and one of the major obstacles for the eradication of the disease is parasite’s resistance to current chemotherapy, new drugs are urgently needed
Specificity and sensitivity of PEGylated cationic QDs (PCQD) for detecting P. falciparum-infected erythrocytes A panel of Quantum dot (QD) with different chemical coatings (QDCOOH, QD-PEG-NH2, QD-mPEG, and PCQD) were characterized with regard to their hydrodynamic sizes, charges, and quantum yield (Table 1)
These welldefined QDs with different charges and sizes were visually screened for their ability to bind iRBCs, and PCQD was found to bind P. falciparum-infected erythrocytes (Figure 1)
Summary
Malaria infects over 300 million people every year and one of the major obstacles for the eradication of the disease is parasite’s resistance to current chemotherapy, new drugs are urgently needed. The CdSe/ZnS semiconductor nanocrystal known as quantum dot (QD) has been widely used for various bioimaging applications as well as in vitro diagnostics due to high photostability, large stokes shift, and tunable narrow emission spectral characteristics [4]. These particular interesting fluorescent properties of QDs allowed it to be used as a robust fluorophore for labelling bacteria [5], red blood cells (RBCs) [6], various intracellular organelles [7], genes [8,9], and proteins [10]. The present study shows (i) a simple and efficient method to label P. falciparum-infected RBC using a QD-based probe and (ii) its applicability as an efficient probe for anti-malarial drug screening
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