Adsorption and thermodynamic properties of azurin at monolayer-protected film assemblies : evidence for a more homogeneous adsorption interface

Thermodynamic and adsorption properties of protein monolayer electrochemistry (PME) are examined for Pseudomonas aeruginosa azurin (AZ) immobilized at an electrode modified with a networked film of monolayer protected clusters (MPCs) to assess if nanoparticle films of this nature offer a more homogeneous adsorption interface compared to traditional self-assembled monolayer (SAM) modified electrodes. Specifically, electrochemistry is used to assess properties of surface coverage, formal potential, electron transfer (ET) kinetics, and peak broadening as a function of film thickness. The modification of a surface with dithiol-linked films of MPCs (Au225C675) provides a more uniform binding interface for AZ that results in voltammetry with less peak broadening (100-105 mV) compared to SAMs (120-130 mV). Improved homogeneity of the MPC interface for protein adsorption is confirmed by atomic force microscopy imaging that shows uniform coverage of the gold substrate topography and by electrochemical analysis of film properties during systematic desorption of AZ, which indicates a more homogeneous population of adsorbed protein. These results suggest MPC film assemblies may be used in PME to provide greater molecular level control of the protein adsorption interface, a development with applications for strategies to study biological ET processes as well as the advancement of biosensor technologies