IMMOBILIZATION OF PROTEIN MOLECULES ONTO HOMOGENEOUS AND MIXED CARBOXYLATE-TERMINATED SELF-ASSEMBLED MONOLAYERS

The attachment of biomolecules, in particular proteins, onto solid sup ports is fundamental in the development of advanced biosensors, biorea ctors, affinity chromatographic separation materials, and many diagnos tic techniques. In addition, the effective investigation of biomolecul ar structure and function with scanning probe microscopy often require s a strong attachment of the biomolecule to a substrate. Here, we inve stigate the binding of the protein catalase to gold surfaces modified by self-assembled monolayers (SAMs). The chemical and physical adsorpt ion of the protein molecules onto SAMs of 8-mercaptopropanoic acid (3- MPA), 11-mercaptoundecanoic acid (11-MUA), and a mixture of the two ac id thiols (mixed) was investigated by utilizing tapping mode atomic fo rce microscopy, scanning tunneling microscopy, surface plasmon resonan ce (SPR), static secondary ion mass spectrometry, and X-ray photoelect ron spectroscopy. The surface concentration of catalase adsorbed on th e SAMs decreased in the following order: mixed, 11-MUA > 8-MPA. Utiliz ing the terminal carboxylic acid functionalities, catalase was immobil ized with a water-soluble carbodiimide and N-hydroxysuccinimide (NHS). Immobilization resulted in increased coverage of the protein. SPR stu dies on silver surfaces modified by these SAMs indicate that immobiliz ation of carbodiimide and NHS decreased in the same order, namely mixe d > 11-MUA > 3-MPA.