Spectral-domain optical coherence phase microscopy for quantitative biological studies

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references.Conventional phase-contrast and differential interference contrast microscopy produce high contrast images of transparent specimens such as cells. However, they do not provide quantitative information or do not have enough sensitivity to detect nanometerlevel structural alterations. We have developed spectral-domain optical coherence phase microscopy (SD-OCPM) for highly sensitive quantitative phase imaging in 3D. This technique employs common-path spectral-domain optical coherence reflectometry to produce depth-resolved reflectance and quantitative phase images with high phase stability. The phase sensitivity of SD-OCPM was measured as nanometer-level for cellular specimens, demonstrating the capability for detecting small structural variation within the specimens. We applied SD-OCPM to the studies of intracellular dynamics in living cells and the detection of molecular interactions on activated surfaces as a sensor application.In the study of intracellular dynamics, we measured fluctuation of localized field-based dynamic light scattering within cellular specimens. With its high sensitivity to amplitude and phase fluctuations, SD-OCPM could observe the existence of two different regimes in intracellular dynamics. We also investigated the effect of an anti-cancer drug, Colchicine and ATP-depletion on the intracellular dynamics of human ovarian cancer cells, and observed the modification in diffusion characteristics inside the cells. Based on the optical sectioning capability of SD-OCPM, quantitative phase imaging was performed to examine slow dynamics of living cells. Through time-lapsed imaging and spectral analysis on the dynamics at the vicinity of cell membrane, we observed the existence of dynamic and independent sub-domains inside the cells that fluctuate at various dominant frequencies with different frequency contents and magnitudes.SD-OCPM was further utilized to measure molecular interactions on activated sensor surfaces.(cont) The method is based on the fact that phase varies as analyte molecules bind to the immobilized probe molecules at the sensing surface and SD-OCPM can measure small phase alteration at any surface with high sensitivity. We have measured a -1.3 nm increase in optical thickness due to the binding of streptavidin on a biotin-activated substrate in a micro-fluidic device. Moreover, SD-OCPM was extended to image protein array chips, demonstrating its potential as a multiplexed protein array scanner.by Chulmin Joo.Ph.D

Spectral-domain optical coherence reflectometric sensor for highly sensitive molecular detection

We describe what we believe to be a novel use of spectral-domain optical coherence reflectometry (SD-OCR) for highly sensitive molecular detection in real time. The SD-OCR sensor allows identification of a sensor surface of interest in an OCR depth scan and monitoring the phase alteration due to molecular interaction at that surface with subnanometer optical thickness sensitivity. We present subfemtomole detection sensitivity for etching of Si

Spectral-domain optical coherence phase and multiphoton microscopy

We describe simultaneous quantitative phase contrast and multiphoton fluorescence imaging by combined spectral-domain optical coherence phase and multiphoton microscopy. The instrument employs two light sources for efficient optical coherence microscopic and multiphoton imaging and can generate structural and functional images of transparent specimens in the epidirection. Phase contrast imaging exhibits spatial and temporal phase stability in the subnanometer range. We also demonstrate the visualization of actin filaments in a fixed cell specimen, which is confirmed by simultaneous multiphoton fluorescence imaging. © 2007 Optical Society of America

Plasma Membrane Temperature Gradients and Multiple Cell Permeabilization Induced by Low Peak Power Density Femtosecond Lasers

Calculations indicate that selectively heating the extracellular media induces membrane temperature gradients that combine with electric fields and a temperature-induced reduction in the electro- permeabilization threshold to potentially facilitate exogenous molecular delivery. Experiments by a wide-field, pulsed femtosecond laser with peak power density far below typical single cell optical de- livery systems confirmed this hypothesis. Operating this laser in continuous wave mode at the same average power permeabilized many fewer cells, suggesting that bulk heating alone is insufficient and temperature gradients are crucial for permeabilization. This work suggests promising opportunities for a high throughput, low cost, contactless method for laser mediated exogenous molecule delivery without the complex optics of typical single cell optoinjection, for potential integration into microscope imaging and microfluidic systems

Diffusive and directional intracellular dynamics measured by field-based dynamic light scattering

Quantitative measurement of diffusive and directional processes of intracellular structures is not only critical in understanding cell mechanics and functions, but also has many applications, such as investigation of cellular responses to therapeutic agents. We introduce a label-free optical technique that allows non-perturbative characterization of localized intracellular dynamics. The method combines a field-based dynamic light scattering analysis with a confocal interferometric microscope to provide a statistical measure of the diffusive and directional motion of scattering structures inside a microscopic probe volume. To demonstrate the potential of this technique, we examined the localized intracellular dynamics in human epithelial ovarian cancer cells. We observed the distinctive temporal regimes of intracellular dynamics, which transitions from random to directional processes on a timescale of ∼0.01 sec. In addition, we observed disrupted directional processes on the timescale of 1∼5 sec by the application of a microtubule polymerization inhibitor, Colchicine, and ATP depletion. © 2010 Optical Society of America

Electrically focus-tuneable ultrathin lens for high-resolution square subpixels.

Owing to the tremendous demands for high-resolution pixel-scale thin lenses in displays, we developed a graphene-based ultrathin square subpixel lens (USSL) capable of electrically tuneable focusing (ETF) with a performance competitive with that of a typical mechanical refractive lens. The fringe field due to a voltage bias in the graphene proves that our ETF-USSL can focus light onto a single point regardless of the wavelength of the visible light-by controlling the carriers at the Dirac point using radially patterned graphene layers, the focal length of the planar structure can be adjusted without changing the curvature or position of the lens. A high focusing efficiency of over 60% at a visible wavelength of 405 nm was achieved with a lens thickness of <13 nm, and a change of 19.42% in the focal length with a 9% increase in transmission was exhibited under a driving voltage. This design is first presented as an ETF-USSL that can be controlled in pixel units of flat panel displays for visible light. It can be easily applied as an add-on to high resolution, slim displays and provides a new direction for the application of multifunctional autostereoscopic displays

Image grating metrology using a Fresnel zone plate

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (p. 107-110).by Chulmin Joo.S.M