Diamond magnetic microscopy of malarial hemozoin nanocrystals

TL;DR

This study uses diamond-based magnetic microscopy to analyze the magnetic properties of malarial hemozoin nanocrystals, revealing their paramagnetic behavior and potential for studying malaria at the cellular level.

Contribution

First application of diamond nitrogen-vacancy centers for imaging magnetic fields of malarial hemozoin nanocrystals at room temperature.

Findings

Most crystals are paramagnetic with a linear magnetic response.

Inferred volume magnetic susceptibility of hemozoin is 3.4×10⁻⁴.

A small subset shows superparamagnetic behavior.

Abstract

Magnetic microscopy of malarial hemozoin nanocrystals was performed using optically detected magnetic resonance imaging of near-surface diamond nitrogen-vacancy centers. Hemozoin crystals were extracted from $Plasmodium$-$falciparum$-infected human blood cells and studied alongside synthetic hemozoin crystals. The stray magnetic fields produced by individual crystals were imaged at room temperature as a function of applied field up to 350 mT. More than 100 nanocrystals were analyzed, revealing the distribution of their magnetic properties. Most crystals ($96\%$) exhibit a linear dependence of stray field magnitude on applied field, confirming hemozoin's paramagnetic nature. A volume magnetic susceptibility $\chi=3.4\times10^{-4}$ is inferred using a magnetostatic model informed by correlated scanning electron microscopy measurements of crystal dimensions. A small fraction of nanoparticles (4/82 for $Plasmodium$-produced and 1/41 for synthetic) exhibit a saturation behavior consistent with superparamagnetism. Translation of this platform to the study of living malaria-infected cells may shed new light on hemozoin formation dynamics and their interaction with antimalarial drugs.