Biomedical Engineering Reference
In-Depth Information
11
Magnetosomes: Bacterial Biosynthesis of Magnetic
Nanoparticles and Potential Biomedical Applications
Sarah S. Staniland
11.1
Introduction
Magnetosomes are magnetic nanocrystals of magnetite within a lipid coating that
are produced biologically (biomineralization) within magnetic bacteria. Such bac-
teria biomineralize magnetosomes in a chain motif of 20-30 units, with the mag-
netic particles produced being responsible for the bacteria aligning and swimming
along magnetic fi eld lines. The biomineralization of these magnetite nanoparticles
is strictly regulated and controlled by the organism, and this results in highly
crystalline, single-domain particles of a highly defi ned shape and size. The mate-
rial, shape, and size of magnetosomes vary for different magnetic bacteria, but are
strictly adhered to within each strain. The magnetite is deposited within a lipid
vesicle that forms the reaction vessel for the biomineralization to occur. This lipid
bilayer then provides a biological, fatty-acid and protein coating for the magnetic
particles. Magnetic bacteria and magnetosomes have been the subject of intensive
research among a range of scientifi c disciplines, from microbiology to paleomag-
netism, and some excellent reviews have been produced [1 - 3] , with more specifi c
literature detailing aspects such as biomolecular magnetosome formation process
[2-7], bacterial phylogeny [8], magnetosome characterization [9], crystal habits [10,
11], magnetism [12], paleomagnetism [13], and geological and environmental sig-
nifi cance [14] .
Interestingly, magnetosomes have been considered for applications in nano-
technology - and particularly for biomedical applications - only relatively recently.
In fact, this area of research is very much in its infancy; to date the only develop-
ment of magnetosomes for biomedical applications has been exclusively for
in
vitro
systems developed at the laboratory of Matsunaga [3, 15]. Research in the fi eld
of biomedical nanotechnology has, however, accelerated rapidly over the past few
years such that today, nanomagnetic particles serve as important biomedical mate-
rials in the development of magnetically targeted therapies. Such therapies utilize
the particles' magnetic properties to guide treatment to a specifi c area, which
means not only lower doses but also fewer adverse side effects. Again, a number
