Spectroscopic studies on the interaction between methylene blue and bovine serum albumin

The interaction between methylene blue (MB) and bovine serum albumin (BSA) was investigated by fluorescence and UV–vis absorbance spectroscopy. In the mechanism discussion, it was proved that the fluorescence quenching of BSA by MB is mainly a result of the formation of MB–BSA complex and electrostatic interactions play an important role to stabilize the complex. The Stern–Volmer quenching constant KSV and corresponding thermodynamic parameters ΔH, ΔG, and ΔS were calculated. The distance r between donor (BSA) and acceptor (MB) was obtained according to fluorescence resonance energy transfer (FRET). The effect of MB on the conformation of BSA has been analyzed by means of UV–vis absorbance spectra and synchronous fluorescence spectroscopy.