The interactions between sodium fluorescein (SoF) and bovine serum albumin (BSA) were investigated by fluorescence spectroscopy. According to the Stern-Volmer equation, the association constants, quenching constants and the numbers of binding sites were obtained. It is proved that the fluorescence quenching of SoF by BSA was a result of the formation of SoF-BSA complex. The thermodynamic parameters for the reaction were calculated according to van t Hoff equation. The distance and energy transfer efficiency between SoF and BSA were obtained according to the theory of non-radioactive energy transfer. The effect of SoF on the conformation of BSA was also analyzed using 3D fluorescence spectroscopy and synchronous fluorescence spectroscopy. The fluorescence intensity of SoF-BSA complex was proportional to the concentration of BSA, based on which, a new quantitative assay of protein was presented. The linear range was 0.15×10^－7～15×10^－7 mol•L^–1, and the sensitivity of the method was high with detection limit of 0.146×10^－8 mol•L^－1. The effects of pH and interfering substance on the detection were also investigated. The results indicated that the most of the water-soluble amino acids, metal ion and antioxidant do not interfer or only interfer slightly under the permission of ±5.0% relative error, whereas SDS, Lecithin, APG, Cu^2＋, Fe^3＋, Sucrose and Tryptophane produced obvious interference. Determination of proteins in human serum by this method gave results which were very close to those obtained by Coomassie Brilliant Blue colorimetry.

Key words: sodium fluorescein, bovine serum albumin, fluorescence spectroscopy, quantitative assay