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Photonic Crystal to Diagnose Malaria

Malaria is caused by the Plasmodium species of protozoans. The symptoms vary considerably depending on the species of Plasmodium infecting the patient. And the main symptom, fever, is common to many other diseases. So diagnosis has to be based on tests.

Microscopic examination of blood smears is commonly used for diagnosis.  This is time consuming and calls for experienced personnel. And, often, the technician might not find any parasite in the blood sample: the occurrence of the parasites in the blood stream has a periodicity and the chances of finding the parasite in the smear depends on the time at which the sample was taken. 

Two falciparum malarial parasites in blood smear
Image: Dr Mae Melvin

Bhuvneshwar Suthar and Anami Bhargava, teaching physics in two colleges in Bikaner, now have a solution, based on the refractive index of blood – the way light bends when it passes through. The frequency of the light that passes through normal blood is maximum at about 813 nanometers. This shifts down in infected blood. And the refractive index of blood changes. If the refractive index can be measured accurately, we could have an easier diagnostic test. 

The duo have been researching photonic crystals – crystals that allow the propagation of specific frequency ranges of light.

They had Ankita, their student, to help out in their experiments. The trio designed a device consisting of alternating thin layers of silicon and fused silica, each of 50 nanometres thickness. They sandwiched a defective layer between two wafers of five layers of silicon and silica each. 

They measured the refractive index at 800 nanometers and measured the refractive indices of the different layers of the photonic crystal at the same wavelength. 

When electromagnetic waves pass through multiple layers, there is reflection besides refraction. Some part of the light is internally reflected multiple times before it passes through. There is a cute technique in physics to make sense of this phenomenon: the transfer-matrix method. If the electric field at the beginning of the first layer is known, the electric field that emerges from the stack of layers can be calculated using matrices, well known operations in mathematics.

In the first infected stage of malaria (ring stage), if the blood sample is introduced into the defect layer, and light is passed through it, the peak transmission wavelength of the defect state shifts from 813.65 nanometers to 807.70 nanometers. Later, when the malarial parasite is actively growing, (trophozoite stage), it is 800,26 nanometers. And, when they are actively dividing (schizont stage), it is 795.31 nanometres. These changes are detected with very high sensitivity by the photonic crystal biosensor in terms of the changes in refractive index. 

“Our photonic crystal biosensor for malaria is less than 12 micrometers thick”, says Bhuvneshwar Suthar, MLB Government College, Bikaner. 

“And the response time is quite low – a matter of femtoseconds”, beams Anami Bhargava, Govt Dungar College, Bikaner.

“A perfect product for a biotechnology start up”, adds Ankita, Maharaja Ganga Singh University, Bikaner.

In 2018, more than 2000 lakh cases of malaria were reported. And, though there are diverse drugs that can treat malaria, more than four lakh people died. Most deaths due to malaria happen because of delay in diagnosis.

The device not only diagnoses malaria, but also detects the stage of infection. If it becomes accessible to clinical practice, imagine the reduction in the number of deaths due to malaria.

DOI: 10.1007/s11468-020-01259-8

Swarnendu Roy
University of North Bengal

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Categorised in: Diagnostics, Medicine, Rajasthan

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