Adsorption of a protein–porphyrin complex at a liquid–liquid interface studied by total internal reflection synchronous fluorescence spectroscopy Original Research Article

Interfacial analysis has attracted more and more attention owing to its fundamental and biological importance. Total internal reflection fluorescence (TIRF) spectroscopy is a useful method to study interfacial properties. The synchronous scanning fluorescence technique provides a selective tool to analyze a specific component in a complex system. The interaction and adsorption of bovine serum albumin (BSA) and meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) at toluene–water interface were studied successfully by the coupling technique of total internal reflection synchronous fluorescence (TIRSF). New methods are provided for the determination of the critical micelle concentration (cmc), apparent adsorption equilibrium constant (Kad) and maximum amount of adsorption (fmax) at the liquid–liquid interface. The results indicated that BSA could adsorb onto the toluene–water interface as a complex of BSA–TPPS in a ratio of 1:1 ratio based on Langmuir adsorption isothermal model. The cmc, apparent Kad and fmax for BSA at pH 3.1 were determined to be 1.0 × 10−4 mol L−1, 1.15 × 105 L mol−1 and 1.14 × 10−9 mol cm−2, respectively.