TY - JOUR A1 - Moser, Marko A1 - Behnke, Thomas A1 - Hamers-Allin, Carolina A1 - Klein-Hartwig, Karin A1 - Falkenhagen, Jana A1 - Resch-Genger, Ute T1 - Quantification of PEG-maleimide ligands and coupling efficiencies on nanoparticles with Ellman's reagent JF - Analytical chemistry N2 - The surface modification of nanometer- and micrometer-sized particles and planar substrates with polyethylene glycol (PEG) ligands of varying length is a very common strategy to tune the hydrophilicity and biocompatibility of such materials, minimize unspecific interactions, improve biofunctionalization efficiencies, and enhance blood circulation times. Nevertheless, simple methods for the quantification of PEG ligands are comparatively rare. Here, we present a new concept for the quantification of PEG ligands for maleimide-functionalized PEG molecules and the determination of PEG coupling efficiencies, exploiting the quantitative reaction of maleimide with ʟ-cysteine, and the subsequent determination of the unreacted thiol with the photometric Ellman's test. This is shown for heterobifunctional PEG spacers of varying length and amino-functionalized polystyrene nanoparticles (PS NP) without and with differently charged encoding dyes. The reaction of ʟ-cysteine with the Ellman's reagent was monitored photometrically and with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) to derive the reaction mechanism and to obtain the stoichiometry factor for ʟ-cysteine quantification. Mass balances and quantification of ʟ-cysteine via its sulfur concentration using elemental analysis and inductively coupled plasma mass spectrometry (ICP-MS) confirmed the accuracy and reliability of this approach that can be extended to other surface groups and ligands. KW - Photometric assay KW - Surface analysis KW - Nanoparticle KW - Polyethylene glycol KW - PEG quantification KW - Ellman's test PY - 2015 DO - https://doi.org/10.1021/acs.analchem.5b02173 SN - 0003-2700 SN - 1520-6882 VL - 87 IS - 18 SP - 9376 EP - 9383 PB - American Chemical Society CY - Washington, DC AN - OPUS4-34468 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hennig, Andreas A1 - Dietrich, Paul A1 - Hemmann, Felix A1 - Thiele, T. A1 - Borcherding, H. A1 - Hoffmann, Angelika A1 - Schedler, U. A1 - Jäger, Christian A1 - Resch-Genger, Ute A1 - Unger, Wolfgang T1 - En route to traceable reference standards for surface group quantifications by XPS, NMR and fluorescence spectroscopy JF - Analyst N2 - The fluorine content of polymer particles labelled with 2,2,2-trifluoroethylamine was reliably quantified with overlapping sensitivity ranges by XPS and solid-state NMR. This provides a first step towards reference materials for the metrological traceability of surface group quantifications. The extension of this concept to fluorescence spectroscopy is illustrated. KW - Polymer beads KW - Poly(acrylic acid)-grafted particles KW - XPS KW - SEM KW - Surface analysis KW - Fluorescent dye labeling KW - NMR PY - 2015 DO - https://doi.org/10.1039/c4an02248c SN - 0003-2654 SN - 1364-5528 VL - 140 IS - 6 SP - 1804 EP - 1808 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-32794 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -