Scope and Limitations of Surface Functional Group Quantification Methods: Exploratory Study with Poly(acrylic acid)-Grafted Micro- and Nanoparticles

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• 作者：Andreas Hennig ; Heike Borcherding ; Christian Jaeger ; Soheil Hatami ; Christian W眉rth ; Angelika Hoffmann ; Katrin Hoffmann ; Thomas Thiele ; Uwe Schedler ; Ute Resch-Genger
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：May 16, 2012
• 年：2012
• 卷：134
• 期：19
• 页码：8268-8276
• 全文大小：384K
• 年卷期：v.134,no.19(May 16, 2012)
• ISSN：1520-5126

文摘

The amount of grafted poly(acrylic acid) on poly(methyl methacrylate) micro- and nanoparticles was quantified by conductometry, ¹³C solid-state NMR, fluorophore labeling, a supramolecular assay based on high-affinity binding of cucurbit[7]uril, and two colorimetric assays based on toluidine blue and nickel complexation by pyrocatechol violet. The methods were thoroughly validated and compared with respect to reproducibility, sensitivity, and ease of use. The results demonstrate that only a small but constant fraction of the surface functional groups is accessible to covalent surface derivatization independently of the total number of surface functional groups, and different contributing factors are discussed that determine the number of probe molecules which can be bound to the polymer surface. The fluorophore labeling approach was modified to exclude artifacts due to fluorescence quenching, but absolute quantum yield measurements still indicate a major uncertainty in routine fluorescence-based surface group quantifications, which is directly relevant for biochemical assays and medical diagnostics. Comparison with results from protein labeling with streptavidin suggests a porous network of poly(acrylic acid) chains on the particle surface, which allows diffusion of small molecules (cutoff between 1.6 and 6.5 nm) into the network.