8-Anilino-1-naphthalenesulfonic acid

8-Anilino-1-naphthalenesulfonic acid (ANS) is a widely used environment-sensitive fluorescent probe for studying protein structure, conformational changes, and hydrophobic surface exposure. ANS exhibits weak fluorescence in aqueous solutions but shows a strong increase in fluorescence intensity and a blue shift in emission upon binding to hydrophobic regions of proteins, membranes, or macromolecular complexes. This property makes ANS an essential tool for protein folding/unfolding studies, ligand-binding assays, and investigations of protein–protein interactions. It is commonly applied in biochemical and biophysical research to monitor changes in protein conformation under varying conditions such as pH, temperature, or denaturant concentration. Spectral data: λex 371 nm, λem 480 nm in methanol.