Congo Red stained sections are typically observed with which microscope?

• A. Brightfield microscope
• B. Polarizing microscope
• C. Fluorescence microscope
• D. Electron microscope

Answer: (B)

The key idea is that Congo red–stained amyloid shows birefringence when viewed with polarized light. Congo red binds along the aligned amyloid fibrils, and under crossed polarizers the ordered beta-pleated sheet structure causes double refraction that appears as an apple-green birefringent signal. This diagnostic feature is only visible with a polarized light microscope, which is why that instrument is the best choice. Brightfield alone won’t reveal the birefringence, fluorescence microscopy isn’t the standard method for this observation, and electron microscopy isn’t used to assess Congo red–induced birefringence.