Optical traps are nowadays quite ubiquitous in biophysical and biological studies. The term is often used synonymously
with optical tweezers, one particular incarnation of optical traps. However, there is another kind of optical trap consisting
of two non-focused, counter-propagating laser beams. This dual-beam trap predates optical tweezers by almost two
decades and currently experiences a renaissance. The advantages of dual-beam traps include lower intensities on the
trapped object, decoupling from imaging optics, and the possibility to trap cells and cell clusters up to 100 microns in
diameter. When used for deforming cells this trap is referred to as an optical stretcher. I will review several applications
of such traps in biology and medicine for the detection of cancer cells, sorting stem cells, testing light guiding properties
of retinal cells and the controlled rotation of cells for single cell tomography.
We have acquired and reconstructed the 3D structures of B16F10 mouse melanoma cells to study morphology
changes in response to gene variations. The 3D structure can be imported into a parallel FDTD code to model light
scattering distribution and determine morphological parameters such as volumes of cytoplasm, nucleus and
mitochondria. We found that the measured parameters agree with the light scatter data obtained with a flow
cytometer, showing significant differences between the genetically modified and the unmodified melanoma cells.
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