Optical Studies and characterization of Plasmodium Falciparum infected human red blood cells

Abstract

In this work, three optical techniques: spectral imaging, laser-induced fluorescence (LIF) and spectrophotometry were used to study and characterize uninfected red blood cells (RBCs) (u-RBCs) and P.falciparum infected RBCs (i-RBCs). Unstained blood smear slides were prepared from blood samples of volunteers who were tested positive for P.falciparum infections (i-blood) and after treatment (u-blood). Optical characteristics of the i-RBCs in spectral images, captured in reflection, scattering and transmission modes, showed increased transmission, and decreased reflection and scattering of light intensity. Histograms fitted with Gaussian curves of aspect ratio (AR) and integrated optical density (IOD) showed mean AR value  1.2 and IOD  2000 a.u for u-RBCs, AR 1.5-2.0 and IOD 5000-13000 a.u for the i-RBCs. In identifying the u-RBCs and the i-RBCs in ring, trophozoite and schizont stages, two spectral bands: 435 nm and 660 nm were found to be common markers in all the three modes. Another spectral band, 470 nm was found to be a shared marker in both reflection and scattering modes. In transmission mode, 590 nm, 625 nm and 700 nm were identified as unique markers for the ring, trophozoite and schizont stages respectively. In both reflection and scattering modes, 525 nm, the 590 nm and the 625 nm were found to be single markers for the ring, trophozoite and schizont stages respectively. LIF results revealed that spectra peak wavelengths of i-blood were red-shifted. The LIF spectra of i-blood samples under Lorentzian curves showed increase in fluorescence spectra peak intensity ratio. The spectrophotometry technique showed reduction in haemoglobin of i-blood at blood absorption bands. These optical techniques may be potentially applied for improved P.falciparum diagnosis.