Quantification of variable functional-group densities of mixed-silane monolayers on surfaces via a dual-mode fluorescence and XPS label

Tobias Fischer, Paul M. Dietrich, Cornelia Streeck, Santanu Ray, Andreas Nutsch, Alex Shard, Burkhard Beckhoff, Wolfgang E.S. Unger, Knut Rurack

Research output: Contribution to journalArticle

Abstract

The preparation of aminated monolayers with a controlled density of functional groups on silica surfaces through a simple vapor deposition process employing different ratios of two suitable monoalkoxysilanes, (3-aminopropyl)diisopropylethoxysilane (APDIPES) and (3-cyanopropyl)dimethylmethoxysilane (CPDMMS), and advances in the reliable quantification of such tailored surfaces are presented here. The one-step codeposition process was carried out with binary silane mixtures, rendering possible the control over a wide range of densities in a single step. In particular, APDIPES constitutes the functional silane and CPDMMS the inert component. The procedure requires only small amounts of silanes, several ratios can be produced in a single batch, the deposition can be carried out within a few hours and a dry atmosphere can easily be employed, limiting self-condensation of the silanes. Characterization of the ratio of silanes actually bound to the surface can then be performed in a facile manner through contact angle measurements using the Cassie equation. The reliable estimation of the number of surface functional groups was approached with a dual-mode BODIPY-type fluorescence label, which allows quantification by fluorescence and XPS on one and the same sample. We found that fluorescence and XPS signals correlate over at least 1 order of magnitude, allowing for a direct linking of quantitative fluorescence analysis to XPS quantification. Employment of synchrotron-based methods (XPS; reference-free total reflection X-ray fluorescence, TXRF) made the traceable quantification of surface functional groups possible, providing an absolute reference for quantitative fluorescence measurements through a traceable measurement chain.

Original languageEnglish
Pages (from-to)2685-2692
Number of pages8
JournalAnalytical Chemistry
Volume87
Issue number5
DOIs
Publication statusPublished - 3 Mar 2015

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    Fischer, T., Dietrich, P. M., Streeck, C., Ray, S., Nutsch, A., Shard, A., Beckhoff, B., Unger, W. E. S., & Rurack, K. (2015). Quantification of variable functional-group densities of mixed-silane monolayers on surfaces via a dual-mode fluorescence and XPS label. Analytical Chemistry, 87(5), 2685-2692. https://doi.org/10.1021/ac503850f