A Lab‐On‐chip Tool for Rapid, Quantitative, and Stage‐selective Diagnosis of Malaria

Abstract

Malaria remains the most important mosquito-borne infectious disease worldwide, with 229 million new cases and 409.000 deaths in 2019. The infection is caused by a protozoan parasite which attacks red blood cells by feeding on hemoglobin and transforming it into hemozoin. Despite the WHO recommendation of prompt malaria diagnosis, the quality of microscopy-based diagnosis is frequently inadequate while rapid diagnostic tests based on antigens are not quantitative and still affected by non-negligible false negative/positive results. PCR-based methods are highly performant but still not widely used in endemic areas. Here, a diagnostic tool (TMek), based on the paramagnetic properties of hemozoin nanocrystals in infected red blood cells (i-RBCs), is reported on. Exploiting the competition between gravity and magnetic forces, i-RBCs in a whole blood specimen are sorted and electrically detected in a microchip. The amplitude and time evolution of the electrical signal allow for the quantification of i-RBCs (in the range 10-10 5 i-RBC µL −1 ) and the distinction of the infection stage. A preliminary validation study on 75 patients with clinical suspect of malaria shows on-field operability, without false negative and a few false positive results. These findings indicate the potential of TMek as a quantitative, stage-selective, rapid test for malaria.

On‐chip magnetophoretic capture in a model of malaria‐infected red blood cells

“…For instance, especially at the early ring stage of infection, the quantities of hemozoin nanocrystals produced by the parasites are variable, and may affect the resulting magnetization of i‐RBCs. Indeed, we previously showed that the magnetophoretic capture of ring‐stage i‐RBCs does occur, but may imply a slower dynamics than the capture of trophozoites (Giacometti et al, 2021 ). Earlier works exploiting magnetophoretic capture under flow also demonstrated different capture capabilities of the same magnetic‐based setting for different‐stage i‐RBCs, with the ring stage representing the most difficult stage to be detected (Karl et al, 2008 ).…”

“…Further exploitation to implement a diagnostic test for malaria requires integrating i‐RBCs counting, in a way suitable for low‐cost, rapid, and on‐site wide screening of the population in endemic zones. In our strategy (Giacometti et al, 2021 ; Milesi et al, 2020 ), we are implementing this via integrated electrical sensors placed close to the concentrating elements of the chip. However other sensor strategies might be used (e.g., magnetic and optical), as well as resorting to automated pattern recognition of optical images at the focal plane of the chip attraction points.…”

“…In view of the development of a simple test suitable for onfield application, not requiring an extensive use of microfluidics, we have recently proposed and successfully tested a capture method in which the selective separation of i-RBCs from h-RBCs occurs applying magnetophoresis to a static sample of gravitysedimenting RBCs (Giacometti et al, 2021;Milesi et al, 2020).…”

“…In view of the development of a simple test suitable for on‐field application, not requiring an extensive use of microfluidics, we have recently proposed and successfully tested a capture method in which the selective separation of i‐RBCs from h‐RBCs occurs applying magnetophoresis to a static sample of gravity‐sedimenting RBCs (Giacometti et al, 2021 ; Milesi et al, 2020 ). The possibility to successfully exploit the competition between magnetic and gravity forces under flow was demonstrated in earlier works (Karl et al, 2008 ; Kasetsirikul et al, 2016 ; Mata‐Cantero et al, 2014 ; Sumari et al, 2016 ; Zimmerman et al, 2006 ).…”

Malaria therapeutics: are we close enough?

“…One such diagnostic technique that has been developed is known as TMek, a lab-on-a-chip diagnostic method that directly quantifies the level of parasitemia (Fig. 8 ) [ 213 ]. It exploits the magnetic properties of hemozoin (malaria pigment) nanocrystals and provides the quantification value in 10 min [ 213 ].…”