89 Mat.-wiss. u. Werkstofftech. 2011, 42, No. 2 DOI 10.1002/mawe.201100737 Synthetic analogues of biogenic magnetite: synthesis and characterization of magnetite nanoparticles Synthetische Nachbildung von biogenem Magnetit: Synthese und Charakterisierung von Magnetit-Nanopartikeln N. O. Dudchenko Biogenic magnetite serve for a wide range of biological functions, including the orientation of animals in the space and also play an important role in the brain functioning. We describe the synthesis and characterization of magnetite nanoparticles that are the synthetic analogues of biogenic magnetite. Magnetite nanoparticles were prepared via co-precipitation of iron (II) and iron (III) with sodium hydroxide in aqueous solution at high temperature (80 8C). To avoid the oxidation of the magnetite surface, further covering of the magnetite nanoparticles with (3- aminopropyl)triethoxysilane was performed. The obtained magnetite nanoparticles had a com- paratively high magnetization (45 A N m 2 /kg) and crystallinity. The average diameter of synthe- sized magnetite nanoparticles was around 14 nm. We could conclude that the characteristics of the synthesized magnetite nanoparticles (size, phase composition, magnetic properties) are similar to biogenic magnetite. Keywords: magnetite / nanoparticles / magnetism / Biogener Magnetit erfüllt eine Reihe biologischer Funktionen, z. B. die räumliche Orientierung von Tieren, und spielt auch eine wichtige Rolle in der Gehirnfunktion. Wir beschreiben die Syn- these und Charakterisierung von Magnetit-Nanopartikeln als synthetische Nachbildungen von biogenem Magnetit. Diese wurden durch Fällung aus Eisen(II)chlorid und Eisen(III)chlorid in Ge- genwart von Natriumhydroxid bei 80 8C erhalten. Zur Verhinderung der Oxidation wurde die Par- tikeloberfläche mit 3-Aminopropyltriethoxysilan funktionalisiert. Die Magnetitnanopartikel wie- sen eine vergleichsweise hohe Magnetisierung (45 A N m 2 /kg) und Kristallinität auf. Der Durch- messer betrug 14 nm. Größe, Phasenzusammensetzung und magnetische Eigenschaften der syn- thetisierten Nanopartikel sind mit den biogenen Magnetitnanopartikeln vergleichbar. Schlüsselwörter: Magnetit / Nanopartikel / Magnetismus / 1 Introduction The research of magnetic biominerals and creation of synthetic analogues of these unique objects is of great importance for solu- tion of a wide range of mineralogical, medical-biological and materials-related problems. The organism of human beings and the organisms of other animals contain magnetite [1, 2, 3]. It is known that biogenic magnetite is the biomineral that ensures the navigation proper- ties of animals (birds, fish, insects, etc.) and takes part in process- ing and saving of information in the brain tissues. However, the mechanism of magnetoreception in the organisms is still unknown. It is known that all sensor systems have specialized receptor cells, that are created for external irritations reaction and these cells are always connected with neurons in order to transfer these informations to the brain. As for magnetorecep- tion, there is yet no evidence of appropriate receptors existence. The final breakthrough in the biophysical arguments against magnetoreception came with the discovery of the magnetotactic bacteria [1] which possess linear chains of either single-domain magnetite (Fe 3 O 4 ) or greigite (Fe 3 S 4 ). These magnetotactic bacte- ria demonstrate a biological activity being influenced by the geo- magnetic field. Biogenic magnetite nanocrystals were firstly discovered in the human brain in 1992 [4]. The results of these investigations denote that the human brain contains a little quantity of ferri- magnetic material. The surface structure and crystallographic parameters of such nanoparticles are similar to biogenic magnet- ite from magnetotactic bacteria. Therefore, it was concluded that these magnetite nanocrystals, were probably created inside human tissues by similar biologically controlled process. After the discovery of nanocrystals of magnetic biominerals in the human brain tissues the question about the role of these biomin- erals in brain functioning and diseases arose. It was shown, e. g., that the quantity of nanomagnetite in the brain tissues was Institute of Geochemistry, Mineralogy and Ore Formation of NAS of Ukraine, 34 Palladina prospect, Kiev 03680, Ukraine Corresponding author: N.O. Dudchenko, M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of NAS of Ukraine, 34 Palladina prospect, Kiev 03680, Ukraine E-mail: ndudchenko@igmof.gov.ua i 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.wiley-vch.de/home/muw