ExCIDS: a combined approach coupling Expansion Microscopy (ExM) and Circular Intensity Differential Scattering (CIDS) for chromatin-DNA imaging

Expansion microscopy (ExM) is a novel preparation method enhancing the optical resolution by expanding uniformly the relative distance between fluorescence molecules on a sample placed inside a polymerized gel matrix. However, a skilled operator is needed for fluorescent labeling protocols and a high light dose is required for measurement. In this work, we couple ExM with a label-free differential circular polarization microscopy technique, demonstrated to be sensitive to the chiral organization of biopolymers. We show that by improving the distance between chiral groups, the new imaging contrast gives access to a better resolution of the chromatin-DNA organization in situ.