Versatile Decoration of Glass Surfaces To Probe Individual Protein−Protein Interactions and Cellular Adhesion

The capability to durably link biological macromolecules to solid supports is fundamental for the development of biosensors and many diagnostic techniques, as well as for the investigation of biomolecular interactions such as adhesion of cells onto biomimetic substrates. Here, we describe two simple and reproducible chemical procedures to decorate glass surfaces with specific ligands at a variable and controlled surface density. The first method uses the streptavidin−biotin complex for further immobilization of biotinylated proteins, while the second method performs a direct covalent attachment of proteins to glass. Both procedures were characterized by optical interferometry to measure molecular-layer thickness, fluorescence flow cytometry to evaluate surface density, and qualitative adhesion/aggregation assays to assay protein functionality. Both routes were first applied to streptavidin as a model protein, and extended to an homotypic calcium-dependent adhesive protein, namely E-cadherin. We mainly discuss key issues that must be addressed when control of the protein surface density and passivation of the surface against nonspecific adsorption are required.