Abstract
Magnetic microscopy of malarial hemozoin nanocrystals is performed by optically detected magnetic resonance imaging of near-surface diamond nitrogen-vacancy centers. Hemozoin crystals are extracted from Plasmodium falciparum–infected human blood cells and studied alongside synthetic hemozoin crystals. The stray magnetic fields produced by individual crystals are imaged at room temperature as a function of the applied field up to 350 mT. More than 100 nanocrystals are analyzed, revealing the distribution of their magnetic properties. Most crystals (96%) exhibit a linear dependence of the stray-field magnitude on the applied field, confirming hemozoin’s paramagnetic nature. A volume magnetic susceptibility of 3.4 × 10−4 is inferred with use of a magnetostatic model informed by correlated scanning-electron-microscopy measurements of crystal dimensions. A small fraction of nanoparticles (4/82 for Plasmodium falciparum–produced nanoparticles and 1/41 for synthetic nanoparticles) exhibit a saturation behavior consistent with superparamagnetism. Translation of this platform to the study of living Plasmodium-infected cells may shed new light on hemozoin formation dynamics and their interaction with antimalarial drugs.
Highlights
Magnetic field sensors based on diamond nitrogenvacancy (NV) centers have emerged as a powerful platform for detecting nanomagnetism in biological samples [1,2]
Hemozoin crystals are a biomarker for malaria, and a substantial effort has been devoted to developing diagnostic platforms based on their detection [10,13]
Our results demonstrate the capability of diamond magnetic microscopy to simultaneously measure the magnetic properties of numerous individual biocrystals
Summary
Magnetic field sensors based on diamond nitrogenvacancy (NV) centers have emerged as a powerful platform for detecting nanomagnetism in biological samples [1,2]. With this technique, magnetic fields from magnetotactic bacteria [3], ferritin proteins [4], magnetically labeled cancer cells [5], and neuronal currents [6] have been detected with a remarkable combination of spatial resolution and sensitivity. Malarial parasites feed on their host’s hemoglobin for essential amino acids, while decomposing the iron complexes into highly toxic free radicals These radicals are subsequently bound into chemically inert elongated crystals (50–1500 nm in size) called “hemozoin” [10,11,12]. Hemozoin detection is used in pharmacological studies of malaria [14], since some antimalarial drugs work by altering hemozoin formation [11,12]
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