The application of the spin label method for studying the adsorption of macromolecules on magnetic nanoparticles

A procedure for using spin-label EPR spectroscopy in studies of the adsorption of macromolecular systems on magnetic nanoparticles and quantitative characterization of adsorption layers was developed. The procedure was based on measurements of the intensity of EPR signals of stable nitroxide radical labels covalently bound with macromolecules. The adsorption of spin-labeled macromolecules on the surface of nanoparticles caused broadening of EPR lines as a result of the dipole interaction of unpaired radical electrons with the magnetic moment of particles, which decreased signal intensity. Multilayer adsorption in aqueous media of biological fibrinogen molecules and synthetic polymer (polyethyleneimine) on magnetite particles with a mean diameter of 17 nm was studied. The method was shown to be applicable to the estimation of the amount of adsorbed macromolecules in multilayer coatings up to ∼40 nm thick.