subject of research:

Magnetic properties of fine magnetic nanoparticles (magnetosomes)

name: A. Džarová

supervisor: Dr M. Timko

The main building of the institute

Our research interests in the section of the magnetism:

preparation magnetic particles : precipitations (synthetic mag. particles) - the chemically synthesized magnetite nanoparticles (Fe3O4) for

biomedical using are covered by thin layer of biocompatible materials or are encapsulated into biodegradable polymers

biomineralizations (natural mag. particles) - a new biological magnetic particles (magnetosomes) was found as a

product of biomineralization process from magnetotactic bacteria. The encapsulation of magnetosomes within the organic membrane provides a natural coating, which ensures superior dispersibility of the Fe3O4 particles and provides excellent target for immobilization biologically active substances

MTB are microorganisms that belong to a heterogeneous group of Gram-negative bacteria with diverse morphologies

and habitats they are a diverse group of aquatic prokaryotes

In my experiments magnetosomes were prepared from MTB strain Magnetotacticum Magnetospirillum :

strain AMB-1 is Gram-negative α-proteobacterium that more oxygen-tolerant and easier to grow on a large scale

MTB orient and migrate along geomagnetic field lines – this ability is based on intracellular magnetic structures known as – MAGNETOSOMES

AMB-1 have single chain of magnetosomes longitudinally traverses the cell

[an intracellular single-magnetic-domain crystal of a magnetic iron mineral (the magnetite) to be enclosed by a membrane (a lipid bilayer admixed with proteins) the membrane is intracellular and may be connected to the cytoplasmic membrane]

Process of Process of magnetosome magnetosome formation :formation :

invagination of the invagination of the cytoplasmic membrane cytoplasmic membrane and vesicle formation and vesicle formation for the magnetosome for the magnetosome membrane precursor membrane precursor

accumulation of accumulation of ferrous/ferric ions in the ferrous/ferric ions in the cell and the vesiclescell and the vesicles

strictly controlled iron strictly controlled iron oxidation–reductionoxidation–reduction

have linear dimensions of 40 to 50 nm and are separated from adjacent particles in the chain by approximately 4 to 10 nm

(the mean size of our magnetosomes estimated from TEM was 34 nm)

the particles are well crystallized with truncated octahedral morphology and are oriented so that [111] faces are perpendicular to the magnetosomes chain axis

the number of magnetosomes per cell is variable within a population, but the average number is typically 10 to 20 magnetosomes per cell

the average number of magnetosomes also varies with culture conditions, especially chelated iron concentration and disolved oxygen tension

Biotechnological Biotechnological applicationsapplications::Magnetosomes can be used:Magnetosomes can be used: for the nondestructive domain analysis of soft mag. materialfor the nondestructive domain analysis of soft mag. material locate magnetic poles on meteoric magnetic grainslocate magnetic poles on meteoric magnetic grains the removal of heavy metals and radionuclides from waterthe removal of heavy metals and radionuclides from water the used of the used of „„Microbial magnetometerMicrobial magnetometer””

a great deal of biological applicationsa great deal of biological applications

for example: for example: - - a potential biomarker for geobiologists

- an ideal system for studying biomineralization

- magnetosomes have been also used for the generation of magnetic antibodies

- as components of medically important biosensors

- incorporated bacterial magnetite particles into eukaryotic cells

- have been used in DNA and RNA isolation procedures

- were also used as carriers for the introduction of DNA into cell

- as contrast agents for magnetic resonance imaging and tumor-specific drug carriers

based on intratumoral enrichment

… and in some other

In our experiment for cultivation Magnetotacticum Magnetospirillum sp. AMB-1 we used medium consisted of (per 1 L medium):

10 mL Wolfe’s vitamin solution 5 mL Wolfe’s mineral solution 0.68 g KH2PO4

0.848 g sodium succinate hexahydrate 0.575 g sodium tartrate dihydrate 0.083 g sodium acetate trihydrate 0.225 mL 0.2% (w/v) resazurin (aqueous) 0.17 g NaNO3

0.04 g ascorbic acid 2 mL 0.01 M ferric quinate

• resazurin was added to media as colorimetric indicator of redox potential

• the pH was adjusted to 6.75 with NaOH

• this medium was prereduced under nitrogen for a period of 1 hour, using copper as a

reducing agent, and was subsequently dispensed into culture tubes in an anaerobic hood

• inoculated tubes were incubated at 25°C for a period of 4 days

Techniques for the isolation and purification of magnetosome particles from Magnetotacticum Magnetospirillum species:

• are based on magnetic separation or a combination of a sucrose-gradient centrifugation and a magnetic separation technique

• these procedures leave the surrounding membrane intact and magnetosome preparations are apparently free of contaminating material

• owing to the presence of the enveloping membrane, isolated magnetosome particles form stable, well-dispersed suspensions

• after solubilization of the membrane by a detergent, the remaining inorganic crystals tend to agglomerate as a result of magnetic attractive forces

• typically, 2.6 mg bacterial magnetite can be derived from a 1000-mL culture of Magnetospirillum sp. AMB-1. for the isolation of the magnetosome particles, we have used the method described by Gorby

MAGNETOSOMES:The prepared magnetosomes in our laboratory were examined by TEM and magnetic measurement

comprise nanometer –sized, membrane-bound crystals (bacterial magnetic particles) of the magnetic iron minerals magnetite

(Fe3O4)

electron micrograph of the magnetosomes reveals that magnetosomes dispersed very well are arranged in bent chains which tend to form closed loops in suspension so as to minimize their magnetic stray field energy

the mean diameter is estimated to be 34 nm

Magnetic properties were examined by SQUID magnetometer Quantum Design:

the saturation magnetization of the magnetosomes was estimated to be 62 emu/g what is smaller than for chemically synthetized magnetite 75 emu/g at room temperature due to presence of nonmagnetic organic layer

the curve of field dependence of magnetization at 293 K exhibited the remanence of 21 emu/g

coercivity of 185 Oe what is connected with fact that the mean diameter (34 nm) is larger than critical size for transition from superparamagnetic to ferrimagnetic behaviour

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PRESENTATIONPRESENTATION

Budapest, HungaryBudapest, Hungary: : 4th Central European 4th Central European Training School on Neutron ScatteringTraining School on Neutron Scattering

FORMATION AND MAGNETIC PROPERTIES OF MAGNETOSOMESFORMATION AND MAGNETIC PROPERTIES OF MAGNETOSOMES A. Džarová, M. Timko, A. Šprincová, P. Kopčanský, J. Kováč, M. Koneracká, I. VávraA. Džarová, M. Timko, A. Šprincová, P. Kopčanský, J. Kováč, M. Koneracká, I. Vávra

Leiden, Netherland: Leiden, Netherland: Magnetic Magnetic Nanoparticles: Challenges and Future Nanoparticles: Challenges and Future Prospects Prospects                        

Thank you for your attentionThank you for your attention