27 April 2006 Local protein/gene density measurements using SMI microscopy
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Spatially Modulated Illumination (SMI) microscopy was applied to determine changes of the local refractive index at discrete fluorescently labeled sites within the cell nucleus. We present measurements on polymerase II complexes, where we found a variation of the local refractive index of 1.38 - 1.55 (standard deviation interval) throughout the nucleus. This variability is not correlated to the accumulations and the extensions of the polymerase II complexes, which have been determined in a previous experiment.1 Local protein accumulations such as adherent transcriptionally active proteins could possibly contribute to such variations, as could also different compactions of the DNA fiber. Altogether, we present a method to precisely obtain a map of the local refractive index inside of cell nuclei, which provides another contrasting mechanism for visualizing sub cellular structures.
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Udo J. Birk, Udo J. Birk, David Baddeley, David Baddeley, Christoph Cremer, Christoph Cremer, } "Local protein/gene density measurements using SMI microscopy", Proc. SPIE 6188, Optical Micro- and Nanometrology in Microsystems Technology, 61880W (27 April 2006); doi: 10.1117/12.668023; https://doi.org/10.1117/12.668023

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