Congo red and Thioflavin T are best set on 4-5 nanometer sections. True or False?

• A. True
• B. False
• C. Not enough information
• D. They are best used on thick sections

Answer: (B)

The statement is false. Staining for Congo red and Thioflavin T is done on sections measured in micrometers, not nanometers. Typical paraffin-embedded tissue sections are about 4–6 micrometers thick (often 4–5 μm), and this thickness allows proper stain penetration and optimal light microscopy visualization, including the apple-green birefringence Congo red can show under polarized light. Nanometer-thick sections are far too thin for light microscopy and for the staining procedures used here, and they cannot be practically produced with standard microtomy.