Absorption and steady state fluorescence study of interaction between eosin and bovine serum albumin.

The interaction between eosin and bovine serum albumin in buffer solution, at pH 7.4 has been studied by means of absorption and emission spectroscopy. Applying the Scatchard model to the absorbance data a non-linear plot was obtained, reflecting a complex process. In the fluorescence spectra, two distinct effects were observed. Upon increasing the protein-dye ratio to about 0.60, the intensity of eosin emission band (544 nm) decreases to approximately 30% of its initial value. During this quenching, a small red shift is noticed. The data were rationalized in terms of two classes of binding sites. At higher protein concentrations, a new band localized at 556 nm appears, which could be assigned to a new fluorescent species. This second process corresponds to a 1:1 binding.