Magneto-optical microscopy offers faster diagnosis of malaria

A magneto-optical microscopy platform developed by the University of Cambridge and Kenya's Kirinyaga University enables faster and objective detection of malaria parasites in blood while also providing quantitative information about the level of parasites present.

Malaria, caused by plasmodium parasites transmitted by mosquitoes, infects over 200 million people around the world each year, causing more than 600,000 deaths. Faster, more objective detection methods are needed to improve diagnosis, guide treatment and enable large-scale screening, especially in low-resource settings.

Optical approaches to malaria diagnosis have been the topic of considerable past research, in particular a long-term effort to use 3D-printed components and smartphone optics to bring cost-effective diagnostic technology to areas where it is most needed.

Described in Biomedical Optics Express the new detection technique leverages the unique properties of hemozoin, a crystal that malaria parasites naturally produce inside red blood cells.

When under an applied external magnetic field the paramagnetic hemozoin crystals align their long axes along the field vector, which duly modulates the optical anisotropy of the specimen. This causes a measurable and field-dependent change in transmitted polarization contrast in imaging data. 

Ratiometric analysis comparing image intensity before and after the magnetic alignment, along with threshold-based segmentation to measure the magneto-optical signal, makes it possible to link the signal strength to hemozoin concentration, providing quantitative information about an infection.

Integration into routine clinical practice

This approach captures both the magnitude of magneto-optical signal and allows the researchers to know where the response is spatially at the microscopic scale.

"Earlier magneto-optical approaches typically provided bulk information about the sample, which can hide important details," commented Dickson Mwenda Kinyua from Kirinyaga University. "With our method, we can detect not only how strong the signal is, but also exactly where it is coming from within the sample. This is all done using relatively simple and accessible components."

In trials, the approach was applied to the imaging of blood samples with and without malaria under a polarizing microscope while applying a magnetic field. The results showed a consistent signal that linearly correlated with the amount of hemozoin present, demonstrating that the method can reliably detect and quantify malaria-related signals.

The establishment of a high-resolution, quantitative imaging platform for spatiotemporal analysis of metabolic processes in malaria parasites is a significant step, commented the project in its paper, and a possible answer to the limitations of clinical light microscopy to this particular issue. A magneto-optical technique transforms the microscope from a purely observational tool to a quantitative biosensor, for faster diagnosis and integration into routine practice across endemic regions. 

"Our method not only makes it possible to see malaria but also allows more precise measurements and the potential to map its location in the sample," said Kinyua. "This quantitative information could be very useful in laboratories and hospitals for faster, more consistent and sensitive diagnosis. It could also make it possible to develop automated approaches for diagnosis."