Surface Engineering of Iron Oxide Nanoparticles Isolated from Magnetospirillum Gryphiswaldense for Biochemical and Biomedical Applications

Superparamagnetic iron oxide nanoparticles with appropriate surface modification can be widely used in various applications including magnetic resonance imaging (MRI) diagnostic contrast agents, anticancer therapy using hyperthermia, magnetic drug targeting, protein and enzyme immobilization, cell labeling and separation or RNA and DNA purification. All these biochemical and biomedical applications require nanoparticles exhibiting a high magnetization and narrow size distribution and possessing non-toxicity and biocompatibility. As a result of biologically controlled preparation, biogenic magnetite (Fe3O4) nanoparticles have properties that make them intrinsically distinct from their synthetic counterparts. Magnetotactic bacteria are microorganisms that are able to biomineralize the membrane-enveloped crystals of magnetite called magnetosomes. Magnetospirillum gryphiswaldense, well laboratory cultured organism, produces cubooctahedral magnetite crystals ranging in size between 20 and 50 nm. The fermentor cultivation under microaerobic conditions, commonly performed in our lab, leads to the sufficiently high cell yield (OD565nm ~ 1.5) and to the suitable values of the parameter describing the cell magnetism (cmag ~ 1). Magnetosomes are consequently isolated from bacteria by method using a neodynium boron (Nd-B) magnet. In the present work, we coated biogenic magnetite with substances that make them biocompatible, biodegradable, stable, non-toxic and accessible for binding with various active biocomponents depending on particular bioapplication. The natural polymers such as chitosan, N-trimethylchitosan, carboxymethylchitosan or dextran have been used in a coating procedure and the properties of the core-shell systems have been analyzed by TEM, SEM and SQUID magnetic measurements. The magnetite nanoparticles modified by chitosan exhibit the most perfect and complete surface stabilization as evidenced by the narrow and well defined shell. These nanoparticles were successfully tested in the trypsin immobilization for applications in proteomics, where they revealed the superior properties compared to the synthetic counterparts.