title: Nanoscale clustering of carbohydrate thiols in mixed self-assembled monolayers on gold.
abstract: Self-assembled monolayers (SAMs) bearing pendant carbohydrate functionality are frequently employed to tailor glycan-specific bioactivity onto gold substrates. The resulting glycoSAMs are valuable for interrogating glycan-mediated biological interactions via surface analytical techniques, microarrays, and label-free biosensors. GlycoSAM composition can be readily modified during assembly by using mixed solutions containing thiolated species, including carbohydrates, oligo(ethylene glycol) (OEG), and other inert moieties. This intrinsic tunability of the self-assembled system is frequently used to optimize bioavailability and antibiofouling properties of the resulting SAM. However, until now, our nanoscale understanding of the behavior of these mixed glycoSAMs has lacked detail. In this study, we examined the time-dependent clustering of mixed sugar + OEG glycoSAMs on ultraflat gold substrates. Composition and surface morphologic changes in the monolayers were analyzed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. We provide evidence that the observed clustering is consistent with a phase separation process in which surface-bound glycans self-associate to form dense glycoclusters within the monolayer. These observations have significant implications for the construction of mixed glycoSAMs for use in biosensing and glycomics applications.
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, Washington 98195, United States.
authors.forename: Faifan
authors.initials: F
authors.lastname: Tantakitti
authors.forename: Jesse
authors.initials: J
authors.lastname: Burk-Rafel
authors.forename: Fang
authors.initials: F
authors.lastname: Cheng
authors.forename: Robert
authors.initials: R
authors.lastname: Egnatchik
authors.forename: Tate
authors.initials: T
authors.lastname: Owen
authors.forename: Matt
authors.initials: M
authors.lastname: Hoffman
authors.forename: Dirk N
authors.initials: DN
authors.lastname: Weiss
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Ratner
mesh_terms: D015374:Biosensing Techniques; D002236:Carbohydrate Conformation; D006046:Gold / Q000737:chemistry*; D008958:Models, Molecular; D036103:Nanotechnology / Q000379:methods*; D011092:Polyethylene Glycols / Q000737:chemistry; D011134:Polysaccharides / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D011134:Polysaccharides; D013438:Sulfhydryl Compounds; D011092:Polyethylene Glycols; D006046:Gold