Properties of Adsorbed Bovine Serum Albumin and Fibrinogen on Self-Assembled Monolayers

We have studied kinetics of adsorption and properties of adsorbed bovine serum albumin (BSA) and fibrinogen (Fb) on a hydrophobic octyl surface, a hydrophilic amine surface, and a mixture of octyl and amine self-assembled monolayer (SAM) and newly synthesized hybrid SAM by using quartz crystal microbalance (QCM). In addition, we have proposed a combined kinetic and mass transfer constrained protein adsorption model. The model is fitted to a change in resonance frequency, ΔF n /n versus time data obtained from QCM to get the kinetic rate constants, mass transfer coefficient, and spreading of adsorbed proteins. Initial rate of adsorption increases with a decrease in surface energy of the substrate. The equilibrium adsorbed amount of BSA on the hybrid surface is less than that on the mixed surface and lies in between that on octyl and amine surfaces and that of Fb is the least on hybrid surface. The analysis of variation of the dissipation factor, ΔD, with ΔF n /n indicates that BSA is more flexible than Fb and the adsorbed layer of both proteins is softest on the hybrid surface. The relaxation times of adsorbed proteins are the slowest on the octyl surface, while those on the hybrid surface are the fastest. The analysis of secondary structures of proteins using ATR-FTIR suggests secondary structures of the proteins change during adsorption. The content of α-helix of the proteins increases due to adsorption on the amine surface, while that decreases on all other surfaces. The total content of α-helix and β-sheet strongly depends on the adsorbed mass of the proteins and is weakly dependent related to elasticity and viscosity of the adsorbed proteins, respectively.