3. Measurement of surface hydrophobicity
Surface hydrophobicity was determined using 1-anilino-8-naphthalene-sulfonate (ANS) as the fluorescence probe (Haskard & Li, 1998). Each sample was diluted to appropriate concentration using 0.1 M phosphate buffer (pH 7.0). Then a 2 mL sample, with concentration ranging from 0.3 to 1.5 mg/mL, was added with a 10 μL 8 mM ANS solution (dissolved in 0.1 M phosphate buffer, pH 7.0). After vortexing, the fluorescence intensity of each sample was determined at an excitation wavelength λex = 374 nm, and an emission wavelength λem = 485 nm. The relationship between the fluorescence intensity as a function of peptide concentration by using the slope of the line was used as the surface hydrophobicity index Ho.