The living cell is criss-crossed by dense networks of filaments providing mechanic stability, site directed molecular transport and support of other vital cell functions. With the polarized light microscope we can observe the birefringence associated with thin filaments or partially oriented filament networks and measure the birefringence directly in the living cell (Fig. 1). Filament birefringence is a consequence of the elongated shape of the molecules and occurs naturally without the need to stain or label them, as is necessary in fluorescence imaging.

We have measured the birefringence of microtubules and axoneme filaments using the new polarized light microscope (Pol-Scope).The design of the Pol-Scope is based on the traditional polarized light microscope in which the crystal compensator is replaced by a universal compensator made from two liquid crystal variable retarders. Electronic image acquisition in the Pol-Scope is synchronized to liquid crystal settings to capture a sequence of four images with circular and elliptical polarization.