Synthesis of magnetic filaments
Éva Bereczk-Tompa1, Ferenc Vonderviszt1,2, Balázs Tóth 1, Mihály Pósfai 1
1
University of Pannonia, Veszprém, 2MTA TTK, Budapest
The equilibrium morphology of magnetite is octahedral and there are several methods for
synthesizing such crystals. However, there is an increasing technological demand for
magnetic nanocrystals with special morphologies and controlled sizes. The concept of the
present project is to build one-dimensional magnetic nanostructures in vitro by using surfacemodified bacterial filaments as templates.
The filament part of the bacterial flagellum is built up from thousands of flagellin
subunits, by a self-assembly process. Using genetic engineering, we modified bacterial
flagella by inserting into the central part of the flagellin natural and synthetic oligopeptides
that are known to bind magnetite (Fe3O4) nanoparticles, while the functional properties of
both partners were preserved (Fig. 1). The self-assembly of the flagellin-based fusion proteins
resulted in mutant filaments displaying periodically repeated recognition sites on their
surfaces that had strong affinity to bind magnetite nanoparticles from their suspension,
providing a biological template for the formation of magnetic nanofibers.
Magnetite nanoparticles were synthesized using the co-precipitation method. Ferrous
and ferric salts were mixed and the reaction mixture was titrated with 1M NaOH. In order to
avoid any oxidation, all solutions were degassed before use and the system was kept under
argon atmosphere during the synthesis. The sample contained aggregates consisting of
nanoparticles in random orientations (Fig. 2a). To prevent the agglomeration of nanoparticles
we successfully used ultrasonic treatment (Fig. 2b), and then added these paricles to the
bacterial cell suspension and incubated at 4ºC for 1 hour. As suggested by TEM images,
magnetite particles bound to the flagellae (Figs. 2c and 2d). Further experiments are in
progress to avoid the agglomeration of magnetite-covered filaments, yielding magnetic
nanotubes.
Fig. 1: (a) Arrangement of flagellin subunits within the bacterial flagellum. The D3 domain is
situated on the filament surface. (b) The D3 domain of flagellin was replaced by magnetitebinding oligopeptides.
Fig. 2: (a) TEM image and corresponding SAED pattern of an aggregate of magnetite
nanocrystals that were prepared by co-precipitation, (b) Ultrasonic treatment was successfully
used to prevent the agglomeration of nanoparticles. (c) and (d) Magnetite nanoparticles
attached to the surfaces of the mutant filaments.