Formaldehyde crosslinks are formed between protein molecules, in particular with the basic amino acid – lysine. Only those lysine residues on the exterior of the protein molecule can react with formaldehyde. Formaldehyde crosslinks are made primarily on the hydrophilic areas of proteins. The reaction between aldehyde and protein is pH-dependent, progressing more rapidly at higher pH values.
Formaldehyde concentrations ranging from 4-10% are often used in fixation buffer. BiCell Scientific has found that lower formaldehyde concentrations such as 1-2% can better preserve antigenicity while higher formaldehyde concentrations such as 4-10% retain good tissue morphology. Formalin-fixed paraffin-embedded (FFPE) sections (formalin: 10% formaldehyde), however, require antigen retrieval processes to revive antigenicity in tissues, which is essential to IHC applications.
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