fixatives

Fixatives are chemical agents used to preserve biological tissues and other materials by stabilizing their structure and preventing decay. In histology and pathology, fixation aims to preserve tissue morphology and, when possible, antigenicity for microscopic analysis. Fixation works primarily by inactivating enzymes and by interacting with cellular proteins to cross-link or precipitate them, thereby hardening the tissue and making it resistant to degradation.

Common fixatives include 10% neutral buffered formalin (formaldehyde in phosphate buffer), paraformaldehyde, glutaraldehyde, ethanol, and methanol, as well as mixtures such as Bouin’s solution or Zenker’s solution. The choice depends on the intended downstream application: formaldehyde- and paraformaldehyde-based fixatives are widely used for light microscopy; glutaraldehyde is favored for electron microscopy due to stronger cross-linking; alcohols are used when preserving certain epitopes or nucleic acids is needed. Fixation is typically followed by dehydration, clearing, embedding, sectioning, and staining. Over-fixation or under-fixation can introduce artifacts and affect antigenicity or nucleic acid preservation.

In art, fixatives are coatings applied to drawings or pastels to prevent smudging and abrasion. Traditional fixatives include starch- or gum-based preparations, while modern products are often acrylic- or shellac-based. Art fixatives can alter color and sheen and may release volatile compounds, so users select products compatible with their media.

Safety and handling: many fixatives are toxic or irritants; proper ventilation, gloves, and disposal procedures are required.