The cell surface proteome plays an important role in fundamental biological processes such as cell signaling, cell-to-cell communication, and nutrient and metabolite transport. Specifically, cell surface receptors bind to extracellular ligands to initiate cellular responses. Because cells express different receptors at different times under various conditions on the cell surface, it is important to monitor and characterize these changes to better understand basic cellular functions. Our group has developed a system to investigate receptor expression patterns on cell surfaces without isolation or purification of the receptors. This system utilizes aldehyde-terminated self assembled monolayers (SAMs) on gold surfaces to react with amine-bearing biomolecules. Protein ligands can be attached to the SAMs through their lysine residues and then capture whole cells through a ligand-receptor interaction. The cell binding patterns can be monitored by phase contrast microscopy and the cell binding density can be determined by cell counting, which allows us to analyze the receptor expression. Currently, we are investigating cell surface receptors involved in stem cell self-renewal and angiogenesis of endothelial cells.