Monitoring of the interaction of tannin with bovine serum albumin by electrochemical quartz-crystal impedance system and fluorescence spectrophotometry

The interaction process of tannin with bovine serum albumin (BSA) was studied by the electrochemical quartz-crystal impedance system (EQCIS) and fluorescence spectrophotometry. The equivalent circuit parameters and resonant frequencies of the piezoelectric quartz-crystal (PQC) resonance, the value of half-peak width of the electroacoustic conductance spectrum (ΔfG1/2) as well as the electrical double-layer capacitance were obtained and analyzed. The results showed that the frequency curve and the double-layer capacitance curve due to BSA adsorption exhibited a character of a sum of exponential functions. Both piezoelectric impedance and fluorescence measurements revealed that the molar ratio of tannin to BSA in the tannin-BSA binding was 2:1. The combining constant (3.6 × 1011 L2 mol−2) was calculated out from the concentration and relative fluorescence intensity based on the Stern-Volmer equation.