Viscoelastic modeling with interfacial slip of a protein monolayer electrode-adsorbed on an acoustic wave biosensor

Transverse-shear mode acoustic wave devices have been used as real-time, label-free detectors of conformational shifts in biomolecules on surfaces. However, material changes in the biochemical monolayers and coupling between the substrate and the surrounding liquid make it difficult to isolate the desired signal, so an understanding of these phenomena is required. An important step in this understanding is knowledge of the material properties of the linker layer that attaches a biochemically selective molecule to the gold surface, in our case, neutravidin. With the goal of obtaining material properties for a neutravidin monolayer, for use in future studies, neutravidin adsorption to the gold surface of an acoustic wave biosensor is described as a viscoelastic monolayer using one-dimensional modeling. Neutravidin is described as forming hydrated, viscoelastic monolayers, and slip is allowed at all interfaces. An impedance model is numerically fit to experimental values using a two-parameter minimization algorithm and values for the shear modulus of the neutravidin monolayer, in agreement with literature values for similar proteins, are obtained. Slip is found on the electrode surface prior to neutravidin adsorption. These results will be used for future modeling studies involving this protein as a linker protein.