Proceedings Article | 11 February 2011
Proc. SPIE. 7902, Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IX
KEYWORDS: Microscopes, Microfluidics, Phase contrast, Calibration, Blood, Argon, Microscopy, Particles, Semiconductor lasers, Optical tweezers
We report red blood cell (RBC) stretching using a Zeiss Axioplan microscope, modified for phase contrast and optical
trapping using a 808 nm diode laser bar, as a tool to characterize RBC dynamics along a linear optical trap. Phase
contrast offers a convenient method of converting small variations of refractive index into corresponding amplitude
changes, differentially enhancing the contrast near cell edges. We have investigated the behavior of RBCs within both
static and dynamic microfluidic environments with a linear optical stretcher. Studies within static systems allow
characterization of cell interactions with the line optical force field without the complicating forces associated with
hydrodynamics. In flowing, dynamic systems, cells stretch along the optical trap down microfluidic channels and are
eventually released to recover their original shape. We record the dynamic cell response with a CMOS camera at 250 fps
and extract cell contours with sub-pixel accuracy using derivative operators. To quantify cell deformability, we measure
the major and minor axes of individual cells both within and outside of the trap, which also allows measurement of cell
relaxation. In these studies, we observe that cell rotation, stretching, and bending along the linear optical trap, are tightly
coupled to the modulation of optical power and cell speed inside our microfluidic systems.
