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

Abstract

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.

Optical nanoscopy

“…The combination of such expansion microscopy expansion techniques with optical nanoscopy methods, including STED [152], STORM [182] and SIM [183], demonstrated the access to finer details of several biological structures. So far, since when the sample buffer is expanded, the density of the chiral structures is reduced, the coupling between expansion and CIDS microscopy produces a global improvement in terms of spatial resolution and imaging contrast [153]. This is only the tip of an iceberg when thinking to merge the advanced optical methods available today in a kind of melting pot that has been named liquitopy, liquid tunable microscopy [164], Fig.…”

“…Recently, expanded specimens have been utilized to improve the resolution and imaging contrast of label-free CIDS [82] scanning microscopy . Such a multimodal approach applied to the chromatin-DNA organization in intact cells has been named ExCIDS [153].…”

Circular Intensity Differential Scattering for Label-Free Chromatin Characterization: A Review for Optical Microscopy

“…Thus, in a following work, we utilized the same technique on whole HEK cells (no nucleus extraction) in conjunction with Expansion Microscopy (ExM) in an approach we named ExCIDS [ 140 ]. The ideas behind this method are explained in Figure 7 .…”

“…( c ) Principle of the SNR decreasing and imaging contrast quality improvement after the expansion process. Reproduced with permission from [ 140 ].…”

“…Here, CIDS is represented in blue, while the fluorescence signal is represented in green. Reproduced with permission from [ 140 ].…”