Autofluorescence is biological fluorescence due to which components?

• A. Chlorophyll
• B. Flavin coenzymes FAD/FMN and NADH
• C. Dyes used in staining
• D. Water molecules

Answer: (B)

Autofluorescence comes from molecules already present inside cells and tissues, not from added stains. The most common endogenous fluorophores are the metabolic cofactors NADH and the flavin coenzymes FAD and FMN. These molecules naturally absorb light and emit fluorescence, which is why tissues can glow under certain excitation wavelengths even without any staining. Chlorophyll can fluoresce, but it’s not typically present in animal tissues and isn’t the general source of autofluorescence in standard immunohistochemistry practice. Dyes used for staining are external agents and produce fluorescence only after staining, not as intrinsic autofluorescence. Water doesn’t contribute meaningful autofluorescence under typical imaging conditions.