Study of Adsorption of Globular Proteins on Hydrophobic Surfaces

In this paper, we use micromachined, high-frequency, quartz bulk acoustic wave resonators to systematically study the physical and viscoelastic properties of spontaneously adsorbed globular protein films with molecular weights (MWs) spanning three decades on hydrophobic surfaces. Specifically, changes in the frequency and the Q -factor of the micromachined resonator array were studied as a function of concentration for five proteins, namely human serum albumin (HSA), immunoglobulin G (IgG), human fibrinogen (Fib), alpha-2-macroglobulin (AMG), and immunoglobulin M (IgM) at the fundamental and third resonance modes. The results obtained were interpreted using equivalent electrical impedance models for the multilayer stack on the quartz crystal microbalances surface. Discrete changes in the protein adsorption and the viscoelastic behavior with solution concentration were observed for all the five protein films. The spherical core-shell protein model is used to provide a simple explanation of the results. The work presents the first systematic and quantitative evaluation of the density, thickness, viscosity, and elastic modulus of adsorbed globular protein films and demonstrates the advantages of using micromachined high-frequency bulk acoustic wave resonators for obtaining these types of data.