Birefringence of a normal human red blood cell and related optomechanics in an optical trap.
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.
Bangalore University, Department of Physics, Jnanabharathi, Bangalore 560056, IndiabM.S. Ramaiah Institute of Technology, Department of Physics, M.S.R. Nagara, Bangalore 560054, India.
Belavadi Venkatakrishnaiah
BV
Nagesh
Bangalore University, Department of Physics, Jnanabharathi, Bangalore 560056, India.
Yogesha
Raman Research Institute, Soft Matter Division, C.V. Raman Avenue, Bangalore 560080, India.
Ramarao
R
Pratibha
Bangalore University, Department of Physics, Jnanabharathi, Bangalore 560056, India.
Praveen
P
Parthasarathi
Bangalore University, Department of Physics, Jnanabharathi, Bangalore 560056, India.
Shruthi Subhash
SS
Iyengar
Bangalore University, Department of Physics, Jnanabharathi, Bangalore 560056, India.
Sarbari
S
Bhattacharya
Bangalore University, Department of Physics, Jnanabharathi, Bangalore 560056, India.
Sharath
S
Ananthamurthy
D000328:Adult; D000818:Animals; D001718:Birefringence; D002645:Chickens; D004912:Erythrocytes / Q000737:chemistry*; D006801:Humans; D008859:Microscopy, Polarization / Q000379:methods; D052898:Optical Tweezers; D055815:Young Adult