samplesfixation

Samples fixation is the set of techniques used to preserve biological or chemical samples in a state close to their native condition by stabilizing structures and immobilizing components. The aim is to prevent degradation, autolysis, and morphological change so that subsequent analyses yield reliable data about the sample’s composition and organization.

Fixation methods are broadly categorized as chemical, physical, or a combination. Chemical fixatives commonly include aldehyde-based agents such as formaldehyde or glutaraldehyde, which crosslink proteins; paraformaldehyde is a widely used alternative. Alcohols like methanol or ethanol and solvent-based fixatives can precipitate proteins or dissolve certain lipids. Osmium tetroxide is used for electron microscopy to preserve and contrast lipid-rich membranes. Physical fixation includes cryofixation by rapid freezing, which minimizes chemical changes and is often followed by freeze-substitution for electron microscopy. High-pressure freezing is another approach that preserves ultrastructure more faithfully in some contexts.

The choice of fixative affects downstream analyses. Fixatives can alter antigenicity, enzymatic activity, or nucleic acid integrity and may introduce artifacts. Therefore compatibility with planned techniques (light or electron microscopy, immunohistochemistry, in situ hybridization, proteomics, or metabolomics) and the required level of structural preservation guide the selection and fixation duration.

Applications span histology, pathology, and research across cell biology and microbiology. Fixed and appropriately prepared samples are routinely embedded for sectioning (for FFPE tissues), mounted on slides for staining, or prepared for advanced imaging and molecular assays. Safety and waste considerations are also important, as many fixatives are hazardous and require proper handling and disposal.

See also: fixation in microscopy, histology, immunohistochemistry, cryofixation, FFPE.