What is a common fixative used in electron microscopy?

Osmium tetroxide is a common fixative used in electron microscopy due to its exceptional ability to preserve cellular ultrastructure. This fixative effectively penetrates biological tissues and cross-links lipids, which is crucial for maintaining the integrity of membrane structures at the nanoscopic level. It also enhances contrast in electron microscopy images, allowing for better visualization of cellular details. The ability to stabilize fats and phospholipids makes osmium tetroxide particularly valuable when preparing samples for high-resolution imaging, as it helps to maintain the fine details of cellular components that would otherwise be lost during the preparation process. Because of these properties, osmium tetroxide is favored over other fixatives for applications requiring the detailed observation of fine structural features.