It has recently been demonstrated that diode laser bars can be used to not only optically trap red blood cells in flowing microfluidic systems but also, stretch, bend, and rotate them. To predict the complex cell behavior at different locations along a linear trap, 3D optical force characterization is required. The driving force for cells or colloidal particles within an optical trap is the thermal Brownian force where particle fluctuations can be considered a stochastic process. For optical force quantification, we combine diode laser bar optical trapping with Gabor digital holography imaging to perform subpixel resolution measurements of micron-sized particles positions along the laser bar. Here, diffraction patterns produced by trapped particles illuminated by a He-Ne laser are recorded with a CMOS sensor at 1000 fps where particle beam position reconstruction is performed using the angular spectrum method and centroid position detection. 3D optical forces are then calculated by three calibration methods: the equipartition theorem, Boltzmann probability distribution, and power spectral density analysis for each particle in the trap. This simple approach for 3D tracking and optical control can be implemented on any transmission microscope by adding a laser beam as the illumination source instead of a white light source.

Date Published: 11 February 2011
PDF: 9 pages
Proc. SPIE 7904, Three-Dimensional and Multidimensional Microscopy: Image Acquisition and Processing XVIII, 79040A (11 February 2011); doi: 10.1117/12.876010

Published in SPIE Proceedings Vol. 7904:
Three-Dimensional and Multidimensional Microscopy: Image Acquisition and Processing XVIII
Jose-Angel Conchello; Carol J. Cogswell; Tony Wilson; Thomas G. Brown, Editor(s)