We report the development of magneto-optic technology for the rapid quantitative diagnosis of malaria that may also be realizable in a noninvasive format. Hemozoin, the waste product of malarial parasitic action on hemoglobin, is produced in a form that under the action of an applied magnetic field gives rise to an induced optical dichroism characteristic of the hemozoin concentration. Here we show that precise measurement of this induced dichroism may be used to determine the level of malarial infection because this correlates, albeit in a complex manner throughout the infection cycle, with the concentration of hemozoin in the blood and tissues of infected patients. Under conservative assumptions for the production of hemozoin as a function of parasitemia, initial results indicate that the technique can match or exceed other current diagnostic techniques. The validity of the approach is confirmed by a small preliminary clinical trial on 13 patients, and measurements on live parasitized cells obtained from in vitro culture verify the possibility of producing in vivo diagnostic instrumentation.

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BackgroundThis study describes the laboratory evaluation of a novel diagnostic platform for malaria. The Magneto Optical Test (MOT) is based on the bio-physical detection of haemozoin in clinical samples. Having an assay time of around one minute, it offers the potential of high throughput screening.MethodsBlood samples of confirmed malaria patients from different regions of Africa, patients with other diseases and healthy non-endemic controls were used in the present study. The samples were analysed with two reference tests, i.e. an histidine rich protein-2 based rapid diagnostic test (RDT) and a conventional Pan-Plasmodium PCR, and the MOT as index test. Data were entered in 2 × 2 tables and analysed for sensitivity and specificity. The agreement between microscopy, RDT and PCR and the MOT assay was determined by calculating Kappa values with a 95% confidence interval.ResultsThe observed sensitivity/specificity of the MOT test in comparison with clinical description, RDT or PCR ranged from 77.2 - 78.8% (sensitivity) and from 72.5 - 74.6% (specificity). In general, the agreement between MOT and the other assays is around 0.5 indicating a moderate agreement between the reference and the index test. However, when RDT and PCR are compared to each other, an almost perfect agreement can be observed (k = 0.97) with a sensitivity and specificity of >95%.ConclusionsAlthough MOT sensitivity and specificity are currently not yet at a competing level compared to other diagnostic test, such as PCR and RDTs, it has a potential to rapidly screen patients for malaria in endemic as well as non-endemic countries.

Insight into the mechanism responsible for the enhanced level of magneto-optical (MO) activity observed from magnetic surfaces when supporting propagating surface plasmons (SPs) is provided by studies of ferromagnetic Ni and Co gratings where SPs are generated and interact magneto-optically at the air/ferromagnetic interface. These ferromagnetic gratings were subsequently coated with semi-transparent Ag layers. In these systems only some 30% of the light incident on the air/Ag interface is reflected; most is converted to surface plasmons whilst the remainder propagates to reflect off the ferromagnetic surface where it undergoes a MO interaction before returning through the Ag. The precise nature of the beam returned from the ferromagnetic and the MO signature imprinted on it depends on the relative magnitude of two driving sources: the E-field of the light wave and the E-field associated with SPs penetrating through the Ag to the ferromagnetic. Evidence is obtained indicating that the degree of MO enhancement correlates strongly with the magnitude of the intense electric field associated with the presence of SPs at the ferromagnetic surface, confirming previous experimental studies postulating that enhanced MO effects are not solely a consequence of the reduction in reflection that is experienced at surface plasmon resonance.

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