title: Kinetics of insulin adsorption at the oil-water interface and diffusion properties of adsorbed layers monitored using fluorescence correlation spectroscopy.
abstract: The adsorption of insulin at an oil-water interface was studied with fluorescence correlation spectroscopy (FCS). FCS is able to measure diffusion properties of insulin at nanomolar concentrations, making it possible to detect the very early steps in the adsorption process. Below 20 nM bulk insulin concentration, the insulin molecules adsorbed to the surface diffuse freely at all times during the experiment (a few hours). At higher concentrations, a surprisingly abrupt transition to a slow diffusion phase is observed. Based on the information about both diffusion times and molecular brightness derived from the FCS experiments, we suggest that the transition represents the formation of a fractal network. FCS may be a valuable tool in pharmaceutical formulation science, because it provides information about concentration buildup and phase changes at interfaces formed in drug delivery systems.
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark. donsmark@physics.leidenuniv.nl
authors.forename: Jesper
authors.initials: J
authors.lastname: Donsmark
authors.forename: Lene
authors.initials: L
authors.lastname: Jorgensen
authors.forename: Susanne
authors.initials: S
authors.lastname: Mollmann
authors.forename: Sven
authors.initials: S
authors.lastname: Frokjaer
authors.forename: Christian
authors.initials: C
authors.lastname: Rischel
mesh_terms: D000327:Adsorption; D000465:Algorithms; D003198:Computer Simulation; D004058:Diffusion; D017709:Fractals; D007004:Hypoglycemic Agents / Q000008:administration & dosage / Q000737:chemistry*; D007328:Insulin / Q000008:administration & dosage / Q000737:chemistry*; D018613:Microscopy, Confocal; D009821:Oils; D013050:Spectrometry, Fluorescence; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water
chemical_list: D007004:Hypoglycemic Agents; D007328:Insulin; D009821:Oils; D014867:Water