title: Optical tracking of anomalous diffusion kinetics in polymer microspheres.
abstract: In this Letter we propose the use of whispering gallery mode resonance tracking as a label-free optical means to monitor diffusion kinetics in glassy polymer microspheres. Approximate solutions to the governing diffusion equations are derived for the case of slow relaxation and small Stefan number. Transduction of physical changes in the polymer, including formation of a rubbery layer, swelling, and dissolution, into detectable resonance shifts are described using a perturbative approach. Concrete examples of poly(methyl methacrylate) and polystyrene spheres in water are considered.
authors.affiliation: Max Planck Institute for the Science of Light, Laboratory of Nanophotonics and Biosensing, Günther-Scharowsky-Straße 1, 91058 Erlangen, Germany.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Foreman
authors.affiliation: Max Planck Institute for the Science of Light, Laboratory of Nanophotonics and Biosensing, Günther-Scharowsky-Straße 1, 91058 Erlangen, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Vollmer
mesh_terms: D004058:Diffusion; D007700:Kinetics; D008863:Microspheres; D008956:Models, Chemical; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D011137:Polystyrenes; D014867:Water; D019904:Polymethyl Methacrylate