Immobilization of proteins on self-assembled monolayers

The immobilization of protein molecules on self-assembled monolayers (SAM) by physical interactions and chemical bonding has been studied using atomic force microscopy (AFM). The proteins used for our investigation are bovine serum albumin (BSA), lysozyme (LYZ), and normal rabbit immunoglobulin G (I gG). The surfaces are methyl-, hydroxyl-, carboxylic acid- and aldehyde-ter minated SAMs. We found that BSA and LYZ can be readily immobilized on SAMs at their isoelectric point (LEP). The detailed surface morphology of adsorb ed proteins varies-with the functionality of the SAMs. The strong hydrophob ic interaction at the IEP is attributed to immobilization. If the solution pH is deviated from the IEP, proteins may be attached onto the surface via electrostatic interactions. Covalent binding between the aldehyde-terminate d SAM and the H2N-groups in the protein results in immobilization of all th ree proteins. The individual proteins and their orientations on SAMs are cl early resolved from high-resolution AFM images. The stability and bioactivi ty of these immobilized proteins are also studied.