For immunofluorescence, the sample is prepared by freezing with no chemical fixation.

• A. Frozen, no fixation
• B. Formalin
• C. Bouin
• D. Glutaraldehyde

Answer: (A)

Immunofluorescence relies on antibodies binding to native antigen sites while the fluorescent label remains intact. Chemical fixatives such as formalin, Bouin, and glutaraldehyde cross-link proteins, which can mask epitopes, alter antigen structure, and increase autofluorescence, all of which diminish antibody binding precision and signal clarity. Freezing with no chemical fixation preserves antigenicity and the fluorophores more effectively, making cryosections or unfixed specimens ideal for immunofluorescence. That’s why this preparation method best supports specific, bright fluorescence signals.