Which fixative is used for GI biopsies and connective tissue (glycogen), lyses RBCs and not use for electron microscopy?

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Bouin's fixative is chosen when the goal is to preserve delicate mucosal and connective tissue architecture, including glycogen-rich areas, for light microscopy. It’s a picric acid–containing mixture (picric acid with formalin and acetic acid) that penetrates quickly and preserves fine details in GI biopsies and connective tissue. The picric acid component also lyses red blood cells, so blood is often cleared from the tissue sections, yielding a cleaner preparation.

However, Bouin's is not suitable for electron microscopy because the fixative disrupts ultrastructure and interferes with resin infiltration, making high-resolution imaging problematic. For EM, aldehyde-based fixatives (like glutaraldehyde, sometimes with osmium tetroxide) are preferred to preserve membranes and fine organelle detail.