Immobilization of Proteins on Carboxylic Acid-Functionalized Nanopatterns
John Peter Ngunjiri, Daniel J. Stark, Tian Tian, Kimberly A. Briggman, Jayne C. Garno
The immobilization of proteins on nanopatterned surfaces was investigated using in situ atomic force microscopy (AFM) and ex situ infrared reflectance-absorption spectroscopy (IRAS). The AFM-based lithography technique of nanografting provided control of the size, geometry, and spatial placement of nanopatterns within self-assembled monolayers (SAMs). Square nanopatterns of carboxylate-terminated SAMs were inscribed within methyl-terminated octadecanethiolate SAMs and activated using carbodiimide/succinimide coupling chemistry. Staphylococcal protein A (SpA) was immobilized on the activated nanopatterns prior to exposure to rabbit immunoglobulin G (IgG). In situ AFM was used to monitor changes in the topography and friction of the nanopatterns in solution. Analysis of height measurements from AFM images was used to determine the orientation of proteins immobilized on the nanopatterns. Complementary studies with ex situ IRAS confirmed the surface chemistry that occurred during the steps of SAM activation and subsequent protein immobilization on unpatterned samples. Since carbodiimide/succinimide coupling chemistry can be used for surface attachment of different biomolecules, this protocol shows promise for development of other aqueous-based studies for nanopatterned protein immobilization.