title: Self-assembled monolayers containing terminal mono-, bis-, and tris-nitrilotriacetic acid groups: characterization and application.
abstract: We have undertaken a structural and functional study of self-assembled monolayers (SAMs) formed on gold from a series of alkylthiol compounds containing terminal multivalent chelators (MCHs) composed of mono-, bis-, and tris-nitrilotriacetic acid (NTA) moieties. SAMs were formed from single-component solutions of the mono-, bis-, and tris-NTA compounds, as well as from mixtures with a tri(ethylene glycol)-terminated alkylthiol (EG(3)). Contact angle goniometry, null ellipsometry, and infrared spectroscopy were used to explore the structural characteristics of the MCH SAMs. Ellipsometric measurements show that the amount of the MCH groups on surfaces increases with increasing mol % of the MCH thiols in the loading solution up to about 80 mol %. We also conclude that mixed SAMs, prepared in the solution composition regime 0-30 mol % of the MCH thiols, consist of a densely packed alkyl layer, an amorphous ethylene glycol layer, and an outermost layer of MCH groups exposed toward the ambient. Above 30 mol %, a significant degree of disorder is observed in the SAMs. Finally, functional evaluation of the three MCH SAMs prepared at 0-30 mol% reveals a consistent increase in binding strength with increasing multivalency. The tris-NTA SAM, in particular, is enabled for stable and functional immobilization of a His6-tagged extracellular receptor subunit, even at low chelator surface concentrations, which makes it suitable for applications when a low surface density of capturing sites is desirable, e.g., in kinetic analyses.
authors.affiliation: Department of Functional Nanomaterials, Institute of Physics, Savanoriu; 231, LT-02300 Vilnius, Lithuania. valiokas@ar.fi.lt
authors.forename: Ramunas
authors.initials: R
authors.lastname: Valiokas
authors.forename: Goran
authors.initials: G
authors.lastname: Klenkar
authors.forename: Ali
authors.initials: A
authors.lastname: Tinazli
authors.forename: Annett
authors.initials: A
authors.lastname: Reichel
authors.forename: Robert
authors.initials: R
authors.lastname: Tampé
authors.forename: Jacob
authors.initials: J
authors.lastname: Piehler
authors.forename: Bo
authors.initials: B
authors.lastname: Liedberg
mesh_terms: D002352:Carrier Proteins / Q000737:chemistry; D007700:Kinetics; D058619:Maltose-Binding Proteins; D008958:Models, Molecular; D015394:Molecular Structure; D009571:Nitrilotriacetic Acid / Q000737:chemistry*; D013053:Spectrophotometry; D013438:Sulfhydryl Compounds / Q000737:chemistry; D020349:Surface Plasmon Resonance
chemical_list: D002352:Carrier Proteins; D058619:Maltose-Binding Proteins; D013438:Sulfhydryl Compounds; D009571:Nitrilotriacetic Acid