Optical phase measurements in red blood cells using low-coherence spectroscopy Itay Shock a , Alexander Barbul b , Pinhas Girshovitz a , Uri Nevo a , Rafi Korenstein b , Natan T. Shaked *a . a Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel. b Department of Physiology-Pharmacology, Faculty of Medicine, Tel Aviv University, Tel Aviv 69978, Israel. Abstract We demonstrate the use of a low-coherence spectral-domain phase microscopy (SDPM) system for accurate quantitative phase measurements in red blood cells (RBCs) for the prognosis and monitoring of disease conditions that affect the visco-elastic properties of RBCs. Using the system, we performed time-recordings of cell membrane fluctuations, and compared the nano-scale fluctuation dynamics of healthy and glutaraldehyde-treated RBCs. Glutaraldehyde-treated RBCs possess a lower amplitude of fluctuations reflecting an increased membrane stiffness. To demonstrate the ability of our system to measure fluctuations of lower amplitudes than those measured by the commonly used holographic phase microscopy techniques, we also constructed a wide-field digital interferometric microscope and compared the performances of the two systems. Due to its common-path geometry, the optical-path-delay stability of SDPM was found to be less than 0.3nm in liquid environment, at least three times better than in holographic phase microscopy under the same conditions. In addition, due to the compactness of SDPM and its inexpensive and robust design, the system possesses a high potential for clinical applications. 1. INTORDUCTION Retrieving quantitative phase information from living, unstained biological samples have given insights to the dynamic mechanisms in cells. Unlike conventional differential interference contrast (DIC) or phase contrast microscopy, which are inherently qualitative, quantitative phase microscopy allows measuring optical path delay (OPD) and topographic data of single point or full-field images 1-5 . Since red blood cells (RBCs) lack intracellular organelles, a constant index of refraction can be assumed on the entire cell’s viewable area. Therefore, the RBC OPD profile measured by quantitative phase microscopy is proportional to the thickness profile of the RBC 6 . Using the time-dependent thickness profile of the RBC, cell stiffness properties can be calculated 7 . Thus, quantitative phase microscopy yields biologically-relevant parameters on live RBCs and can be used as a powerful tool for research and diagnosis. The elastic properties of RBCs, defining their deformability, are dependent on the bending and shearing properties of the cell membrane, which are governed mostly by metabolically regulated coupling between the lipid bilayer and the underlying spectrin-actin cytoskeletal network 8-10 . This deformability is vital as it enables the RBC to squeeze through the small capillaries that are only several micrometers in size. Certain pathological conditions in RBCs such as * nshaked@tau.ac.il ; phone/fax +972 3 640 7100; www.tau.ac.il/~nshaked/ Biomedical Applications of Light Scattering VI, edited by Adam P. Wax, Vadim Backman, Proc. of SPIE Vol. 8230, 82300D · © 2012 SPIE · CCC code: 1605-7422/12/$18 · doi: 10.1117/12.907262 Proc. of SPIE Vol. 8230 82300D-1 Downloaded From: http://spiedigitallibrary.org/ on 05/07/2013 Terms of Use: http://spiedl.org/terms