Apurba Paul, Ponnan Padmapriya, Vasant Natarajan
In previous work studying the properties of red blood cells (RBCs) held in an optical tweezers trap, we observed an increase in the spectrum of Brownian fluctuations for RBCs from a Plasmodium falciparum culture—due to increased rigidity of the cells—compared to normal RBCs. We wanted to extend the study to patient samples, since the earlier work was done with cultures grown in the lab. Individual RBCs were held in an optical-tweezers trap. Its position fluctuations were measured and the power spectrum determined. The corner frequency (fc) of the spectrum gave a quantitative measurement of the spectrum. The value of fc was 25 Hz for normal cells, which increased to 29 Hz for infected cells—both for P. falciparum and Plasmodium vivax infections. The technique of measuring fc can be used as a screening tool for malaria in patients with fever, since RBCs not carrying the parasite will also show the change due to the bystander effect, irrespective of whether it is caused by P. falciparum or P. vivax.
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