Investigation of spontaneously adsorbed globular protein films using high-frequency bulk acoustic wave resonators

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 (MW) spanning two orders of magnitude. Specifically, changes in the frequency and the β-factor of the micromachined resonator array were studied as a function of concentration for three proteins, namely Human Serum albumin (HSA), Immunoglobulin G (IgG) and Human Fibrinogen (Fib) at the fundamental and third resonance modes. The results obtained were interpreted using equivalent electrical impedance models for the multilayer stack on the QCM surface. Discrete changes in the protein adsorption rate constant and the viscoelastic behavior was observed for all the three protein films. The spherical core-shell protein model is used to provide a simple explanation of the results. The work presented is a systematic and quantitative evaluation of the density, thickness, viscosity, and elastic modulus of the globular protein films, which was possible, due the use of the micromachined high frequency bulk acoustic wave resonators.