Visualizing microtubules and other cytoskeletal structures in most types of living cells has been a difficult problem. A new type of microscopy, called modulated polarization microscopy, which can routinely image individual microtubules and other cytoskeletal structures as well as vesicle movements along cytoskeletal tracks will be developed. Modulated polarization microscopy images cytoskeletal structures based on their birefringence but takes advantage of the fact that birefringence is sensitive to polarization angle. When birefringent structures are illuminated with plane polarized light of varying angle and viewed between crossed polarizers they oscillate in intensity. This behavior is not seen with structures that are not birefringent and provides a means for separating weakly birefringent elements from the cytoplasmic background. A prototype instrument has been built using Faraday rotators to modulate the plane of polarized light presented to the specimen. Images obtained using this microscope demonstrate its potential for imaging the cytoskeleton. An advanced version of the moldulated polarization microscope with greatly improved sensitivity, contrast, image quality, and resolution will be built. Improvements in the new microscope will be based on analysis of problems with the original prototype.
