Immuno-electron microscopy cannot be performed on tissues fixed with osmium tetroxide. true or false?

• A. True
• B. False
• C. Only for certain protocols
• D. Osmium tetroxide enhances immuno-EM

Answer: (A)

The main idea is how fixation affects antigen accessibility for antibody binding in immuno-EM. Osmium tetroxide is excellent for preserving membranes and giving strong electron density, but it cross-links and masks protein epitopes, making antibody access to target antigens unreliable. Because immuno-EM depends on specific antibody labeling to localize the antigen, tissues fixed with osmium tetroxide generally cannot be labeled effectively under standard protocols. Some specialized approaches exist (such as labeling before osmication or using milder fixatives), but these are not the typical immuno-EM workflows. Hence, the statement is true.