title: Functionalized self-assembled monolayers on ultraflat gold as platforms for single molecule force spectroscopy and imaging.
abstract: Single molecule force spectroscopy is a valuable tool for studying unfolding and nanomechanical properties of proteins. The common practice is to stretch proteins from a surface that was dosed to give a reasonable hit rate and to analyze the curves that exhibit the expected characteristics of a single polymer. Whether the surface-bound proteins are indeed single and isolated remains unclear, and the undesirable protein/surface interactions that obscure informative features of the force curves are implicitly assumed to be absent. In this study, mixed self-assembled monolayers (SAMs) consisting of N-hydroxysuccinimide (NHS) and oligoethylene glycol (OEG) terminated thiols on an ultraflat gold surface were used to covalently immobilize proteins via lysine residues. By the optimization of attachment sites via lysine-NHS linkages amidst a protein-resistant layer of the OEG SAM, it was possible to isolate single proteins for study in a controlled fashion. The single protein distribution on the surface is clearly demonstrated by atomic force microscopy (AFM) imaging. The OEG also significantly reduces nonspecific tip-surface interactions between the cantilever and surface. Stretching covalently attached single proteins produces high-quality and reproducible force-extension curves. This experimental strategy is an attractive platform with which to study protein structure, interactions, and nanomechanical properties of single proteins.
authors.affiliation: Muscle Proteomics and Nanotechnology Section, Laboratory of Muscle Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health/DHHS, Bethesda, MD 20892, USA.
authors.forename: Vamsi K
authors.initials: VK
authors.lastname: Yadavalli
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Forbes
authors.forename: Kuan
authors.initials: K
authors.lastname: Wang
mesh_terms: D006046:Gold / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D011506:Proteins / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D011506:Proteins; D006046:Gold