Aditya K. Dharmadhikari

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We demonstrate rotation of live Chlamydomonas reinhardtii cells in an optical trap; the speed and direction of rotation are amenable to control by varying the optical trapping force. Cells rotate with a frequency of 60-100 rpm; functional flagella are shown to play a decisive role in rotation. The rotating cells generate torque (typically ~7500-12000 pN nm)(More)
A laser-based method has been developed for experimentally probing single red blood cell (RBC) buckling and determining RBC membrane rigidity. Our method combines a liquid flow cell, fluorescence microscopy, and an optical-trap to facilitate simple measurements of the shear modulus and buckling properties of single RBCs, under physiological conditions. The(More)
We report on optical trapping in a weakly absorbing medium, hemin, an iron-containing porphyrin that is an important component of hemoglobin. By altering the hemin concentration we are able to control the amount of optical energy that is absorbed; changing the hemin concentration from <12 mg/ml to >45 mg/ml enables the onset of thermal trapping to be(More)
Tank-treading (TT) motion is established in optically trapped, live red blood cells (RBCs) held in shear flow and is systematically investigated under varying shear rates, temperature (affecting membrane viscosity), osmolarity (resulting in changes in RBC shape and cytoplasmic viscosity), and viscosity of the suspending medium. TT frequency is measured as a(More)
We investigate the physics of an optically driven micromotor of biological origin. When a single, live red blood cell (RBC) is placed in an optical trap, the normal biconcave disc shape of the cell is observed to fold into a rod-like shape. If the trapping laser beam is circularly polarized, the folded RBC rotates. A model based on geometric considerations,(More)
A combined experimental and theoretical study is carried out to probe the rotational behavior of red blood cells (RBCs) in a single beam optical trap. We induce shape changes in RBCs by altering the properties of the suspension medium in which live cells float. We find that certain shape anisotropies result in the rotation of optically trapped cells.(More)
We have made and characterized a new, erbium-doped tellurite glass that has high glass transition temperature. Addition of phosphate is found to increase the phonon energy. The peak emission cross section is 6 x 10(-21) cm(2) at 1537 nm and the fluorescence lifetime of the (4)I(13/2)-(4)I(15/2) transition is 4.1 ms. We have written 2-D channel waveguides in(More)
We demonstrate ultrashort (6 ps), multimegagauss (27 MG) magnetic pulses generated upon interaction of an intense laser pulse (10(16) W cm(-2), 100 fs) with a solid target. The temporal evolution of these giant fields generated near the critical layer is obtained with the highest resolution reported thus far. Particle-in-cell simulations and(More)
We have used optical tweezers to trap normal and Plasmodiuminfected red blood cells (iRBCs). Two different facets of the behavior of RBCs in infrared light fields emerge from our experiments. Firstly, while the optical field modifies both types of RBCs in the same fashion, by folding the original biconcave disk into a rod-like shape, iRBCs rotate with(More)
Optically trapped single cells of the biflagellated, green alga, Chlamydomonas reinhardtii, rotate. The rotational dynamics of trapped wild-type and mutant cells show that functional flagella play a decisive role: the entire flagellar apparatus (central microtubules, radial spokes, and dynein arms) is involved. Any aberration in this apparatus leads to(More)