title: Scope and limitations of surface functional group quantification methods: exploratory study with poly(acrylic acid)-grafted micro- and nanoparticles.
abstract: The amount of grafted poly(acrylic acid) on poly(methyl methacrylate) micro- and nanoparticles was quantified by conductometry, (13)C 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.
authors.affiliation: BAM Federal Institute for Materials Research and Testing, Richard-Willstätter-Strasse 11, D-12489 Berlin, Germany. andreas.hennig@bam.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Hennig
authors.forename: Heike
authors.initials: H
authors.lastname: Borcherding
authors.forename: Christian
authors.initials: C
authors.lastname: Jaeger
authors.forename: Soheil
authors.initials: S
authors.lastname: Hatami
authors.forename: Christian
authors.initials: C
authors.lastname: Würth
authors.forename: Angelika
authors.initials: A
authors.lastname: Hoffmann
authors.forename: Katrin
authors.initials: K
authors.lastname: Hoffmann
authors.forename: Thomas
authors.initials: T
authors.lastname: Thiele
authors.forename: Uwe
authors.initials: U
authors.lastname: Schedler
authors.forename: Ute
authors.initials: U
authors.lastname: Resch-Genger
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry* / Q000378:metabolism; D001710:Biotin / Q000378:metabolism; D001952:Bridged-Ring Compounds / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry; D008863:Microspheres; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D019904:Polymethyl Methacrylate / Q000737:chemistry; D019809:Streptavidin / Q000378:metabolism; D013499:Surface Properties; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils
chemical_list: D000180:Acrylic Resins; D001710:Biotin; D001952:Bridged-Ring Compounds; D005456:Fluorescent Dyes; D007093:Imidazoles; D019904:Polymethyl Methacrylate; D019809:Streptavidin; C456276:cucurbit(7)uril; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils; C006903:carbopol 940