Discipline: Biological Sciences
Subcategory: Cell and Molecular Biology
Akash Kota - University of Dayton
Co-Author(s): Benjamin Zeke Chancey, Old Dominion University, Norfolk, VA; Denis Kiprop Lagat, Norfolk State University, Norfolk,VA; Darius Luna, Norfolk State University, Norfolk, VA; Sacharia Albin, Norfolk State University; Makarand Deo, Norfolk State University, Norfolk, VA.
Optical stretcher (OS) is a tool that uses two counter propagating, slightly diverging, and identical laser beams to trap an object. OS after its demonstration by Guck et al , is used vividly in biology to measure the elasticity of biological cells. When a soft dielectric object or a biological cell is placed on the optical axis of two counter propagating laser beams, the transverse gradient forces of light beams confine the cell to the optical axis and trap it at a point where the scattering forces of the two laser beams balance each other. As the refractive index of the buffer medium outside the cell is less than that of the enclosed medium inside the cell, the reflection and refraction of light at the cell-body interface causes change in photon momentum which leads to cell stretching. Various analytical models have been proposed to formulate the change in momentum in a light beam at the cell interface [1-2]. Previous formulations assumed the biological cell as a cube  and a sphere  to determine the force acting on the surface of the cell. In this work, the stress profiles on the surface of a biological cell in a dual-beam OS are analyzed numerically by approximating the cell as sphere. Simulations are performed by choosing the physical parameters of silica and polystyrene beads, and human erythrocytes and embryonic kidney cells. By keeping the incident beam power constant and varying the distance between the cell and the tip of the optical fiber, different stress profiles are obtained numerically in MATLAB. Qualitatively, from the obtained numerical results it is evident that by keeping the incident beam power constant, the on-axis magnitude of the stress decreases by increasing the distance. In other words, if the two counter propagating laser beams coming from the two optical fibers are moved away from the cell, the magnitude of the surface stress decreases. Alternatively, when the distance is kept constant and the incident beam power is varied, the shape of the stress profile remains same but as the incident beam power increases the magnitude of the stress increases. This indicates that to increase the magnitude of the stress without altering the stress profile, the incident beam power should be increased. It can be observed that the on-axis stress magnitude increases linearly with increase in the incident beam power. In future, the theoretical stress profiles will be confirmed by experiments using human embryonic kidney cells. The research will be extended to study the effect of stress on altered electrophysiology of excitable biological cell.
 J. Guck et al, ‘The optical stretcher: a novel laser tool to micromanipulate cells,’ Biophys. J. 81, 767-784 (2001).
 P. Bareil et al, ‘Photonics force distribution on spherical cell membrane in optical stretcher,’ Proc. SPIE 6343, 63430D (2006).Not Submitted
Funder Acknowledgement(s): This work is supported in part by NSF grant awarded to Dr. Makarand Deo, Assistant Professor, Department of Engineering, Norfolk State University, Norfolk, VA-23504
Faculty Advisor: Dr. Makarand Deo, firstname.lastname@example.org
Role: In this work the author investigated various analytical models to determine the magnitude of force and there by stress acting on the surface of biological cells. A particular model is chosen and the stress profiles of different soft dielectric objects and biological cells are analyzed numerically in MATLAB.