Which aldehyde is used to preserve biological specimens?

Formaldehyde

Formaldehyde, a simple organic compound with the chemical formula \(CH_2O\), is widely used for preserving biological specimens in a process called formalin fixation. Here's a detailed explanation of why formaldehyde is used for this purpose:

Preservation of Biological Specimens:

1. Fixation: When biological specimens (such as tissues, cells, or whole organisms) are collected for scientific study, they need to be preserved to prevent decay and maintain their structural integrity. Formaldehyde is a powerful fixative used for this purpose.

2. Cross-Linking Proteins: Formaldehyde works by chemically cross-linking proteins. It forms covalent bonds with amino acid residues, primarily lysine, and histidine, in proteins, effectively "fixing" or stabilizing them. This process prevents the degradation of proteins and maintains their structural and functional properties.

3. Preventing Decomposition: Formaldehyde also inhibits the growth of bacteria, fungi, and other microorganisms that can decompose the specimen. This antimicrobial property helps to ensure the long-term preservation of the biological sample.

4. Tissue and Cell Preservation: Formaldehyde fixation is commonly used in histology (the study of tissues) and cytology (the study of cells). It allows for the preparation of tissue sections and cell smears that can be stained and examined under a microscope for diagnostic or research purposes.

5. Fixation Mechanism: Formaldehyde reacts with amino groups \((-NH_2)\) in proteins and other biomolecules to form methylene bridges \((-CH_2-)\), effectively "locking" the biomolecules in place. This cross-linking process imparts rigidity and stability to the specimen.

6. Gradual Dehydration: After fixation, the specimen is usually dehydrated using a series of ethanol or methanol solutions to replace water in the tissues. This process further aids in preserving the specimen by preventing water-induced degradation.

Safety and Handling:

It's essential to note that formaldehyde is a strong irritant, and prolonged exposure can be harmful. Proper safety precautions, including the use of personal protective equipment, well-ventilated spaces, and adherence to safety guidelines, are necessary when working with formaldehyde.

In summary, formaldehyde is a widely used aldehyde for the preservation of biological specimens due to its ability to cross-link proteins, inhibit microbial growth, and maintain the structural integrity of tissues and cells. It has played a crucial role in scientific research, pathology, and medical diagnostics by enabling the long-term storage and examination of biological samples.