A SCANNING PROBE MICROSCOPY STUDY OF THE PHYSISORPTION AND CHEMISORPTION OF PROTEIN MOLECULES ONTO CARBOXYLATE TERMINATED SELF-ASSEMBLED MONOLAYERS

Scanning probe microscopy offers the possibility of investigating biom olecular structure and function. However, successful imaging is techni cally limited by interactions between the probe and the sample. A stro ng attachment of the biomolecule to the substrate is often required. H ere, we investigate the binding of the protein catalase to gold surfac es modified by self-assembled monolayers (SAMs). The chemical and phys ical adsorption of the protein molecules onto SAMs of 3-mercaptopropan oic acid (3-MPA), 11-mercaptoundecanoic acid (11-MUA) and a mixture of the two acid thiols (Mixed) was investigated utilizing tapping mode a tomic force microscopy (AFM), scanning tunneling microscopy (STM) and surface plasmon resonance (SPR). The surface concentration of catalase adsorbed on the SAMs decreased in the order: Mixed > 11-MUA > 3-MPA. Utilizing the terminal carboxylic acid functionalities, catalase was i mmobilized with a water soluble carbodiimide and N-hydroxysuccinimide (NHS). Immobilization resulted in increased coverage of the protein. S PR studies on silver surfaces modified by these SAMs indicate immobili zation of carbodiimide and NHS decreased in the order: Mixed > 11-MUA > 3-MPA.