Abstract
It has recently been shown that a red blood cell (RBC) can be used as optically driven motor. The mechanism for rotation is however not fully understood. While the dependence on osmolarity of the buffer led us to conclude that the osmolarity dependent changes in shape of the cell are responsible for the observed rotation, role of ion gradients and folding of RBC to a rod shape has been invoked by Dharmadhikari et al to explain their observations. In this paper we report results of studies undertaken to understand the dynamics of a RBC when it is optically tweezed. The results obtained support our earlier conjecture that osmolarity dependent changes in shape of the cell are responsible for the observed rotation.
Highlights
There exists considerable interest in optically controlled orientation or rotation of microscopic objects for applications in microfluidics and nano-technology
While the dependence on osmolarity of the buffer led us to conclude that the osmolarity dependent changes in shape of the cell are responsible for the observed rotation [8], role of ion gradients and folding of red blood cell (RBC) has been invoked by Dharmadhikari et al [9, 10] to explain their observations
At the same trap power levels the time required for a RBC to switch from initial horizontal position to the vertical orientation was found to decrease with increasing osmolarity
Summary
There exists considerable interest in optically controlled orientation or rotation of microscopic objects for applications in microfluidics and nano-technology. It has recently been shown that RBC can be used as optically driven motor [8,9,10]. While the dependence on osmolarity of the buffer led us to conclude that the osmolarity dependent changes in shape of the cell are responsible for the observed rotation [8], role of ion gradients and folding of RBC has been invoked by Dharmadhikari et al [9, 10] to explain their observations. Our results do not support the suggestion [9, 10] that RBC folds into rod shape when optically tweezed. A ray optic analysis of the propagation of trap beam through the RBC is presented to explain the observed rotation
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