title: Fabrication and characterization of ultrathin dextran layers: Time dependent nanostructure in aqueous environments revealed by OWLS.
abstract: Surface coatings of the polysaccharide dextran and its derivatives are key ingredients especially in label-free biosensors for the suppression of non-specific binding and for receptor immobilization. Nevertheless, the nanostructure of these ultrathin coatings and its tailoring by the variation of the preparation conditions have not been profoundly characterized and understood. In this work carboxymethylated dextran (CMD) was prepared and used for fabricating ultrathin surface coatings. A grafting method based on covalent coupling to aminosilane- and epoxysilane-functionalized surfaces was applied to obtain thin CMD layers. The carboxyl moiety of the CMD was coupled to the aminated surface by EDC-NHS reagents, while CMD coupling through epoxysilane molecules was performed without any additional reagents. The surface analysis following the grafting procedures consisted of X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared spectroscopy (ATR-IR), spectroscopic ellipsometry, atomic force microscopy (AFM) and optical waveguide lightmode spectroscopy (OWLS). The XPS and AFM measurements showed that the grafting resulted in a very thin dextran layer of a few nanometers. The OWLS method allowed devising the structure of the interfacial dextran layers by the evaluation of the optogeometrical parameters. The alteration in the nanostructure of the CMD layer with the chemical composition of the silane coverage and the pH of the grafting solution was revealed by in situ OWLS, specifically, lain down chains were found to be prevalent on the surface under neutral and basic conditions on epoxysilylated surfaces. The developed methodologies allowed to design and fabricate nanometer scale CMD layers with well-controlled surface structure, which are very difficult to characterize in aqueous environments using present instrumentations and highly hydrated surface layers.
authors.affiliation: Nanobiosensorics Laboratory, Centre for Energy Research, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, Budapest 1121, Hungary. Electronic address: saftics@mfa.kfki.hu.
authors.forename: Andras
authors.initials: A
authors.lastname: Saftics
authors.affiliation: Nanobiosensorics Laboratory, Centre for Energy Research, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, Budapest 1121, Hungary.
authors.forename: Sándor
authors.initials: S
authors.lastname: Kurunczi
authors.affiliation: Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, Budapest 1121, Hungary.
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Szekrényes
authors.affiliation: Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, Budapest 1121, Hungary.
authors.forename: Katalin
authors.initials: K
authors.lastname: Kamarás
authors.affiliation: Microtechnology Department, Centre for Energy Research, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, Budapest 1121, Hungary.
authors.forename: Nguyen Quoc
authors.initials: NQ
authors.lastname: Khánh
authors.affiliation: Thin Film Physics Department, Centre for Energy Research, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, Budapest 1121, Hungary.
authors.forename: Attila
authors.initials: A
authors.lastname: Sulyok
authors.affiliation: MTA-ELTE Research Grup of Peptide Chemistry, Hungarian Academy of Sciences and Eötvös Lóránd University, Pázmány Péter sétány 1/A, Budapest 1117, Hungary.
authors.forename: Szilvia
authors.initials: S
authors.lastname: Bősze
authors.affiliation: Nanobiosensorics Laboratory, Centre for Energy Research, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, Budapest 1121, Hungary.
authors.forename: Robert
authors.initials: R
authors.lastname: Horvath
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D003911:Dextrans / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D049329:Nanostructures / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D011092:Polyethylene Glycols; D012821:Silanes / Q000737:chemistry*; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D003911:Dextrans; D012821:Silanes; D014867:Water; D011092:Polyethylene Glycols; C014392:carboxymethyl dextran
keywords: Anisotropy; Dextran; Grafting; OWLS; Ultrathin layer