Abstract

The physical expansion of biological samples in 3‐D to obtain nanoscale (~70 nm) resolution using light microscopy employing hydration‐competent polymers, an approach termed expansion microscopy (ExM), has not been applied to assess the extent of expansion between different tissues and subcellular organelles, critical to clinical pathological assessments. Ultrastructure of cellular organelles at the nanoscale using electron microscopy, and the distribution of associated antigens, can reflect cell health and is used in the detection and assessment of a wide range of pathologies. Using light microscopy, we performed organelle‐specific fluorescent immunocytochemistry on formalin‐fixed paraffin‐embedded human and rabbit tissue slices, and formalin‐fixed primary human muscle cell cultures, to determine the extent of expansion between different tissues and subcellular organelles. Optical evaluation of subcellular expansion of various organelles in the same and in different tissues demonstrate differential expansion, critical to the rapid and inexpensive optical evaluation, as opposed to electron microscopy. The differential expansion of cellular organelles indicates a growing need to better understand the interactions of the polymers with subcellular structures, the composition of different cellular organelles, and the differences of organelle composition between tissues, before ExM can be applied as a replicable clinical tool.