Ultrasensitive Phase-Resolved Imaging of Cellular Morphology and Dynamics
Microscopy is an important imaging tool in modern clinical medicine and basic biomedical research. Although microscopy is centuries old, cutting-edge research in techniques such as confocal microscopy, fluorescence microscopy, and quantitative phase microscopy continues at a rapid pace. The retrieval of phase information from microscopic samples has a long history  initiated by the development of the phase contrast microscope. Phase contrast microscopy is routinely employed for live visualization of cells, since it enhances subcellular contrast. This technique exploits the fact that optically thin samples such as cells diffract light secondary to local variations in optical index. A phase plate and matching phase annulus added to the light train of a standard compound microscope can be used to interfere diffracted and undiffracted light. The degree of interference is manifest in the amplitude of the detected image. In this way, even unstained cells become distinguishable from their surroundings (Fig. 25.1). Frits Zernike was awarded the Nobel Prize for Physics in 1953 for this development.
Phase contrast microscopy has had an immeasurable impact by allowing the user to qualitatively visualize small, subcellular variations in optical index. Quantative phase microscopy seeks to build upon the principles of Zernike to extract information relating to optical index, birefringence, motion, and flow. In addition to highlighting subcellular detail in unstained cells, quantitative phase techniques can measure small cell motions, small changes in cell index, and cytoplasmic flow.
KeywordsDoppler Shift Phase Noise Doppler Frequency Fourier Domain Optical Index
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