Monthly Colloquium

How Biological Tissues respond to external forces? An Optical Tweezers study


A tightly focused laser beam can "trap" micron-sized dielectric objects just like an "Optical Tweezers", as its inventor "Arthur Ashkin" named it. The nature of the force acting on the irradiated object depends on several parameters, the most important of which being size and material of the object as well as the wavelength and wave front geometry of the irradiation. It can be shown that a TEM00 laser beam, which is focused through a lens with millimeter-range focal length, can exert a Hookean force on a dielectric object with a refractive index greater than that of the surrounding medium. This hallmark of optical tweezers allows for very accurate force spectroscopy inside aqueous solution, provided that its spring constant is already known. Typically this constant is determined before the main experiment by one calibration procedure. Though the above-mentioned single-trap optical tweezers covers most of their applications, however, several variation of the instrument is recently introduced. For instance, it is shown than phase modulation of the wave front of the converging beam could provide more than a single trapping site. Using this method an optical lattice with few hundreds of trapping sites are presented. Optical Tweezers have found several applications in biology as their achievable force range fits very well to the forces ruling the biological interactions in the cellular (and sub-cellular) level. In this talk I will go through couple of biological applications of optical tweezers in the molecular and sub-cellular scale. I will show how optical tweezers can uncover mechanical properties of biological structures such as mRNA molecules, cell membranes, and even entire human Red Blood Cells (RBCs). .

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Seminar Speaker:
Dr. S. Nader Seyed Reihani
Date :
19 Jul. 2017
Time :
Farmaniyeh Building, Conference Hall
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