* Corresponding author. Tel.: #49-331-567-9235; fax: #49- 331-567-9202. E-mail address: voigt@mpikg-golm.mpg.de (A. Voigt). Journal of Magnetism and Magnetic Materials 225 (2001) 59}66 Novel polyelectrolyte multilayer micro- and nanocapsules as magnetic carriers Andreas Voigt*, Norbert Buske, Gleb B. Sukhorukov, Alexei A. Antipov, Stefano Leporatti, H. Lichtenfeld, Hans BaK umler, Edwin Donath, Helmuth MoK hwald Max-Planck-Institute of Colloids and Interfaces, D-14424 Potsdam/Golm, Germany Mediport Kardiotechnik GmbH, Wiesenweg 10, D-12247 Berlin, Germany Institute of Transfusion Medicine, Medical Faculty Charite& , Humboldt-University of Berlin, D-10098 Berlin, Germany Abstract Polyelectrolyte multilayer (PEM) capsules are introduced as versatile magnetic carrier systems. Superparamagnetic magnetite is mounted to the multilayer shell itself or is a component of the capsule interior. The PEM is formed at di!erent (decomposable) colloidal templates, e.g. melamine formaldehyde resin, glutaraldehyde "xed red blood cells, emulsion oil droplets. The results are illustrated by transmission electron microscopy and confocal laser scanning microscopy.  2001 Elsevier Science B.V. All rights reserved. Keywords: Microcapsules; Polyelectrolyte multilayers; Magnetic carriers; Confocal laser scanning microscopy; Transmission electron microscopy; Erythrocyte 1. Introduction Polyelectrolyte multilayer (PEM) micro- and nanocapsules were introduced [1,2] as an extension of PEM on #at substrate surfaces [3}5]. When decomposable colloids are used as templates they can be removed after completion of the PEM coat- ing and `hollowa capsules or shells are obtained [6,7]. Surprisingly, they are very stable in di!erent aqueous and organic solvents. Recently, the collo- idal PEM were combined with superparamagnetic magnetite [8}10]. Colloidal PEM are easily fabricated in a layer-by-layer procedure [2,8] which is algorithmic and iterative that means it can be carried out continuously with a high degree of automatization. More e!ective `single stepa formu- lations based on complex precipitation are applied now and can be used alone or in combination with the layer-by-layer approach [11,12]. One of the advantages of PEM capsules is their versatility of physical and chemical properties by variation of composition and fabrication as well as application conditions. Several dozen of natural and synthetic polyelectrolytes or other charged substances are suitable as layer components, e.g. chitosan, chitosansulfate, poly(L-lysine), poly(acrylic acid), poly(diallyldimethylammonium chloride), 0304-8853/01/$ - see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 1 2 2 8 - 2