14 November 2014 Birefringence of a normal human red blood cell and related optomechanics in an optical trap
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A normal human red blood cell (RBC) when trapped with a linearly polarized laser, reorients about the electric polarization direction and then remains rotationally bound to this direction. This behavior is expected for a birefringent object. We have measured the birefringence of distortion-free RBCs in an isotonic medium using a polarizing microscope. The birefringence is confined to the cell’s dimple region and the slow axis is along a diameter. We report an average retardation of 3.5±1.5  nm for linearly polarized green light (λ=546  nm). We also estimate a retardation of 1.87±0.09  nm from the optomechanical response of the RBC in an optical trap. We reason that the birefringence is a property of the cell membrane and propose a simple model attributing the origin of birefringence to the phospholipid molecules in the lipid bilayer and the variation to the membrane curvature. We observe that RBCs reconstituted in shape subsequent to crenation show diminished birefringence along with a sluggish optomechanical response in a trap. As the arrangement of phospholipid molecules in the cell membrane is disrupted on crenation, this lends credence to our conjecture on the origin of birefringence. Dependence of the birefringence on membrane contours is further illustrated through studies on chicken RBCs.
© 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
Belavadi Venkatakrishnaiah Nagesh, Belavadi Venkatakrishnaiah Nagesh, . Yogesha, . Yogesha, Ramarao Pratibha, Ramarao Pratibha, Praveen Parthasarathi, Praveen Parthasarathi, Shruthi Subhash Iyengar, Shruthi Subhash Iyengar, Sarbari Bhattacharya, Sarbari Bhattacharya, Sharath Ananthamurthy, Sharath Ananthamurthy, } "Birefringence of a normal human red blood cell and related optomechanics in an optical trap," Journal of Biomedical Optics 19(11), 115004 (14 November 2014). https://doi.org/10.1117/1.JBO.19.11.115004 . Submission:

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