Hemozoin-catalyzed precipitation polymerization as an assay for malaria diagnosis

Abstract

Methods to diagnose malaria are of paramount interest to eradicate the disease. Current methods have severe limitations, as they are either costly or not sensitive enough to detect low levels of parasitemia. Here we report an ultrasensitive, yet low-resource chemical assay for the detection and quantification of hemozoin, a biomarker of all Plasmodium species. Solubilized hemozoin catalyzes the atom transfer radical polymerization of N-isopropylacrylamide above the lower critical solution temperature of poly(N-isopropylacrylamide). The solution becomes turbid, which can be observed by naked eye and quantified by UV-visible spectroscopy. The rate of turbidity increase is proportional to the concentration of hemozoin, with a detection limit of 0.85 ng mL−1. Malaria parasites in human blood can be detected down to 10 infected red blood cells μL−1. The assay could potentially be applied as a point-of-care test. The signal-amplification of an analyte by biocatalytic precipitation polymerization represents a powerful approach in biosensing.

Rapid quantification of the malaria biomarker hemozoin by improved biocatalytically initiated precipitation atom transfer radical polymerizations

“…However, the reaction does not proceed as typical reversible-deactivation radical polymerization due to the heterogeneous nature of the reaction mixture. 28 Even though oxygen interferes with radical polymerizations, the solution is not deoxygenated to allow for point-of-care handling of the assay.…”

“…We have previously shown that the rate of turbidity formation depends on the hemozoin concentration, making the test quantitative. 28 The higher the concentration of dissolved hemozoin is, the faster the rate of turbidity formation is. However, turbidity forms even in the absence of a catalyst (Fig.…”

“…1a), can be used to catalyze radical polymerizations. 28 We exploited this phenomena to design a polymerization-amplified assay for the detection of hemozoin and, therefore, of malaria parasites. Hemoglobin can also be detected by the assay in a sensitive way.…”

“…41 Our polymerizationamplified hemozoin detection technique is a very sensitive method for detecting hemozoin concentrations down to 0.85 ng mL −1 at a confidence level of 95%. 28 To evaluate the performance of the technique, hemozoin was extracted from blood samples spiked with different amounts of cultured parasites. A limit of detection (LOD) of 10 infected red blood cells per μL was achieved, demonstrating the possible application of this technique as a sensitive diagnostic test for malaria.…”

On-Chip Selective Capture and Detection of Magnetic Fingerprints of Malaria

“…Consequently, infected red blood cells (i-RBCs) exhibit paramagnetic properties depending on their crystals content. In the last year, many different approaches to malaria diagnosis based on malaria biomarkers have been proposed [ 19 , 20 , 21 , 22 , 23 , 24 , 25 ].…”