Opto-magnetic Detection of Malaria: a Potential Low-cost, Rapid, and Sensitive Malaria Screening Method

Abstract

Malaria is a sickness transmitted by a bite of female Anopheles mosquito which carries a Plasmodium parasite. Malaria is prevalent in Sub-Saharan Africa, parts of South America, Asia and portions of Central America. In the year 2017, close to 219 million people were infected with malaria with an estimate of 435000 deaths globally according to the WHO report. The malaria deaths are mainly associated with late diagnosis and lack of screening kits as most of these places are remote and less resourced. The commonly used screening methods include: PCR (polymerase chain reaction), RDT (Rapid Diagnostic Tests) and Giesma microscopy which are expensive and require specialist to operate. This work involved fabrication of a portable and rapid malaria screening device. The device composed of an LED, lenses, a pair of disc magnets, a photo-diode and a screen. This battery powered device was applied in the detection of hemozoin (malaria pigment) first when suspended in de-ionized water and later in rat’s blood. The absorption spectra (measured using a spectrophotometer) of hemozoin suspensions were obtained. Prominent absorption bands were observed at around 377, 421 and 449 nm assigned to SoS2 transitions (Soret/B-band) 551, 665, 723 and 866 nm assigned to So-S1 transitions (Q-band) in hemozoin. Transmittance of LED light emitting at 450 nm and 667 nm decreased with concentration of hemozoin. This was due to absorption by hemozoin. These LEDs were used in the malaria screening device. The voltage difference detected by the photodiode indicated nonlinear relationship with concentration. The transmittance was also measured using the malaria device in presence and absence of magnetic field. When graphs of voltage against concentration were plotted, the fit equation was obtained and the trend was equation of the form y=kLn(x)+ C which can be equivalently expressed as 𝑒 = 𝑦−𝑐 𝑘 In this relation, y and x represented the voltage and hemozoin concentration respectively. The later equation was used as malaria diagnostic algorithm as it (x) in the sample. The R2 values obtained for the curve in the presence of magnetic field was 0.983 and was higher than that without the magnetic field which was 0.971. This indicated that taking the measurements in the presence of magnetic field was better and makes the device more sensitive. This also supported the idea that the magnetic field influences the orientation of hemozoin nanocrystals such that majority are aligned in a certain way.