On the adsorption kinetics of bovine serum albumin at the air–water interface

The adsorption kinetics of bovine serum albumin (BSA) at an air–water interface was investigated by experimentally measuring and theoretically modeling the dynamic surface tension (ST) data. A pendant bubble tensiometer was utilized for two ST measurements: (i) the adsorption onto a freshly created bubble surface and (ii) the bubble expansion/compression at the latter stage. The dynamic ST data, during the early stage of BSA adsorption, were best-fitted with the short-time approximation equation (diffusion-control) and the non-asymptomatic short-time formalism [mixed-control, Moorkanikkara and Blankschtein, JCIS, 296, 442–457 (2006)]. The fitting showed that the non-asymptotic short-time formalism could well predict the dynamic ST data; thereby, implying that the adsorption of BSA onto a clean air–water interface was mixed-controlled. A new approach for estimating the maximum surface concentration (Γ_∞) and the intermolecular interaction amongst the adsorbed BSA molecules (K) was trialed. The relaxation of ST during a surface expansion was best-fitted with the Langmuir/Frumkin equation of state. A reasonably good fitting between the dynamic ST data and the theoretical ST profiles indicated that this approach could be used to estimate the Γ_∞ and K for BSA without requiring the equilibrium ST data.