la703709a_si_002.pdf (693.42 kB)
Self-Assembled Monolayers Containing Terminal Mono-, Bis-, and Tris-nitrilotriacetic Acid Groups: Characterization and Application
journal contribution
posted on 2008-05-06, 00:00 authored by Ramūnas Valiokas, Goran Klenkar, Ali Tinazli, Annett Reichel, Robert Tampé, Jacob Piehler, Bo LiedbergWe 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 (EG3). 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.