Hydrophobic/hydrophilic interactions of cytochrome c with functionalized self-assembled monolayers on silicon

Cytochrome c (Cc, horse heart) has been adsorbed onto self-assembled monolayers (SAM) on silicon single crystal substrates. Layer thickness was determined using ellipsometry and atomic force microscopy in the DFM tapping mode. Both hydrophilic (COOH containing SAM) and hydrophobic self-assembled monolayers were used. The protein layers were found to consist of adsorbed 2-dimensional islands. Concentration, exposure time and the defect-density of the self-assembled monolayer substrates determined the wetting properties of the resulting layer, indicating that the surface orientation of the protein is driven by the interaction with the substrate. On well ordered self-assembled monolayers, the protein layer thicknesses were 1.76 nm for charged surfaces and 2.3 nm for hydrophobic surfaces. Self-assembled monolayers of a lower density resulted in a prevalence of Cc islands of 3.2 nm thickness for both cases. (C) 2003 Elsevier Science B.V. All rights reserved.