Determination of accessible amino groups on surfaces by chemical derivatization with 3,5-bis(trifluoromethyl)phenyl isothiocyanate and XPS/NEXAFS analysis |
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Authors: | Nora Graf Andreas Lippitz Thomas Gross Falko Pippig Andreas Holländer Wolfgang E S Unger |
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Institution: | 1. BAM VI.43—Surface and Thin Film Analysis, Bundesanstalt für Materialforschung und -prüfung, Unter den Eichen 44-46, 12203, Berlin, Germany 2. Fraunhofer-Institut für Angewandte Polymerforschung, Geiselbergstr. 69, 14476, Potsdam, Germany
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Abstract: | The determination of amino groups on surfaces capable of binding biomolecules is important for the understanding and optimization
of technologically relevant coupling processes. In this study, three different types of amino-functionalized model surfaces,
amino thiolate on Au, amino siloxane on Si, and polyethylene (PE) foils and films reacted with 1,2-diaminoethane (DAE) were
derivatized with 3,5-bis(trifluoromethyl)phenyl isothiocyanate. Subsequently, these samples were analyzed by chemical derivatization
X-ray photoelectron spectroscopy (CD-XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The determination
of amino groups by this analytical approach allows gaining insight into the availability of groups on surfaces that can actually
serve as attachment sites for biomolecules in technical applications. In the case of the amino thiolate on Au, almost 90%
of the expected amino groups were detected by CD-XPS. Investigation of the amino siloxane films revealed lower yields for
the derivatization reaction in the order of 30%. The lowered reaction yields are thought to be due to interactions between
the amino siloxane’s amino and silanol groups or the underlying substrate, making them inaccessible to the derivatization
agent. The aminated PE samples are characterized by a complex surface chemistry and structure, and reaction yields of the
derivatization reaction cannot be unequivocally derived. However, 1–3% of the total carbon atoms in the surface layer were
found to be bound to amino groups accessible to the derivatization agent. It can be concluded that, depending on the detailed
character of the investigated amino-terminated surface, the amount of amino groups accessible to CD-XPS can be substantially
lower than the total amount of amino groups present at the surface. |
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