In situ synthesis and characterization of magnetic nanoparticles in shells of biodegradable polyelectrolyte microcapsules

摘要

Hollow microcapsules with the shell composed of biodegradable polyelectrolytes modified with the maghemite nanoparticles were fabricated by in situ synthesis. The nanoparticles were synthesized from the iron salt and the base directly on the capsule shells prepared by "layer by layer" technique. An average diameter of the capsule was about 6.7 mu m while the average thickness of the capsule shell was 0.9 mu m. XRD, HRTEM, Raman and Mbssbauer spectroscopy data revealed that the iron oxide nanoparticles have the crystal structure of maghemite gamma-Fe2O3. The nanoparticles were highly monodisperse with medium size of 7.5 nm. The Mossbauer spectroscopy data revealed that the nanoparticles have marked superparamagnetic behavior which was retained up to room temperature due to slow spin relaxation. Because of that, the microcapsules can be handled by an external magnetic field. Both these properties are important for target drug delivery. Based on the Mossbauer spectroscopy data, the spin blocking temperatures TB of about 90 K was found for the particles with size D <= 5 nm and T-B approximate to 250 K for particles with D >= 6 nm. The anisotropy constants K were determined using the superparamagnetic approximation and in the low temperature approximation of collective magnetic excitation. (C) 2014 Elsevier B.V. All rights reserved.