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M. L. Fdez-Gubieda et al.
purity, and easy reproducibility, they display a high magnetic moment and, very
importantly, they are surrounded by a lipid-protein membrane, which confers them
stability avoiding aggregation of extracted magnetosomes, easy functionalizability,
and biocompatibility. Here we will review some of the potential applications of
magnetosomes and MTB, with special focus on biomedical applications, and will
discuss the main drawbacks that are delaying the transfer of the magnetosome-based
technology to the market.
Magnetic hyperthermia is a therapy that aims at debilitating cancer cells by delivering heat to them. In magnetic hyperthermia the magnetic nanoparticles are attached
to or internalized into the tumor cells and an alternating magnetic field (AMF) is
applied. Under the action of the AMF, the magnetic moment of the nanoparticles
describes a hysteresis loop, whose area is proportional to the dissipated energy that
increases the temperature of the tumor. By reaching temperatures around 40–45
◦ C
in the tumor area, the cancer cells can be ‘deactivated’ (dead or driven to apoptosis) without affecting the healthy ones. The study of magnetic nanoparticles with
high heating capability, namely large hysteresis loop area for a given magnetic field
intensity H and frequency f , has generated wide interest. In this context, magnetosomes from M. gryphiswaldense [63–66] and M. magneticum [66, 67] have been
proven to exhibit large specific absorption rate (SAR) values at AMFs within the
clinical limits (H · f ≤ 5 × 10
9 Am
−1 s
−1 [68]), constituting ideal candidates for
magnetic hyperthermia. The SAR values observed for magnetosomes are considerably higher than those for chemically synthesized magnetite nanoparticles [69–71].
This is mainly attributed to the magnetosomes being single magnetic domains stable
at room temperature, a condition met by magnetosomes due to their size (between
30 and 50 nm for M. gryphiswaldense and M. magneticum), sizes that otherwise are
hardly achievable with synthetic procedures.
As an example, Fig. 7.10a shows the SAR values normalized by the frequency
(SAR/ f ) for magnetosomes from M. gryphiswaldense dispersed in water as a function of the applied magnetic field amplitude. For the studied field and frequency
ranges the SAR/ f values are independent of the frequency, evidencing a linear
dependence of SAR with frequency. The efficiency of these magnetosomes as hyperthermia agents at 24 kA/m and 149 kHz has been tested on macrophages [64]. Results
show that the hyperthermia treatment causes both cell death and inhibition of cell
proliferation. Specifically, only 36% of the treated macrophages remained alive 2 h
after alternating magnetic field exposure, 24 h later the percentage fell to 22% (see
Fig. 7.10b).
The magnetosome membrane provides a matrix for the functionalization of the
magnetosomes with biomolecules of interest and is a unique characteristic of magnetosomes over synthetic magnetic nanoparticles. Functionalization is possible either
by chemical modification of the isolated particles or by genetic engineering of magnetosome membrane proteins. Genetic approaches involve fusing magnetosome membrane proteins to other enzymes or proteins of interest [72]. Functionalization opens
up a wide range of applications in which magnetosomes bind specifically to cells, proteins, or nucleic acids of interest that are subsequently separated, detected or guided
with magnetic fields [4]. For example, Ginet et al. [73] engineered a nanobiocatalyst
M. L. Fdez-Gubieda et al.
purity, and easy reproducibility, they display a high magnetic moment and, very
importantly, they are surrounded by a lipid-protein membrane, which confers them
stability avoiding aggregation of extracted magnetosomes, easy functionalizability,
and biocompatibility. Here we will review some of the potential applications of
magnetosomes and MTB, with special focus on biomedical applications, and will
discuss the main drawbacks that are delaying the transfer of the magnetosome-based
technology to the market.
Magnetic hyperthermia is a therapy that aims at debilitating cancer cells by delivering heat to them. In magnetic hyperthermia the magnetic nanoparticles are attached
to or internalized into the tumor cells and an alternating magnetic field (AMF) is
applied. Under the action of the AMF, the magnetic moment of the nanoparticles
describes a hysteresis loop, whose area is proportional to the dissipated energy that
increases the temperature of the tumor. By reaching temperatures around 40–45
◦ C
in the tumor area, the cancer cells can be ‘deactivated’ (dead or driven to apoptosis) without affecting the healthy ones. The study of magnetic nanoparticles with
high heating capability, namely large hysteresis loop area for a given magnetic field
intensity H and frequency f , has generated wide interest. In this context, magnetosomes from M. gryphiswaldense [63–66] and M. magneticum [66, 67] have been
proven to exhibit large specific absorption rate (SAR) values at AMFs within the
clinical limits (H · f ≤ 5 × 10
9 Am
−1 s
−1 [68]), constituting ideal candidates for
magnetic hyperthermia. The SAR values observed for magnetosomes are considerably higher than those for chemically synthesized magnetite nanoparticles [69–71].
This is mainly attributed to the magnetosomes being single magnetic domains stable
at room temperature, a condition met by magnetosomes due to their size (between
30 and 50 nm for M. gryphiswaldense and M. magneticum), sizes that otherwise are
hardly achievable with synthetic procedures.
As an example, Fig. 7.10a shows the SAR values normalized by the frequency
(SAR/ f ) for magnetosomes from M. gryphiswaldense dispersed in water as a function of the applied magnetic field amplitude. For the studied field and frequency
ranges the SAR/ f values are independent of the frequency, evidencing a linear
dependence of SAR with frequency. The efficiency of these magnetosomes as hyperthermia agents at 24 kA/m and 149 kHz has been tested on macrophages [64]. Results
show that the hyperthermia treatment causes both cell death and inhibition of cell
proliferation. Specifically, only 36% of the treated macrophages remained alive 2 h
after alternating magnetic field exposure, 24 h later the percentage fell to 22% (see
Fig. 7.10b).
The magnetosome membrane provides a matrix for the functionalization of the
magnetosomes with biomolecules of interest and is a unique characteristic of magnetosomes over synthetic magnetic nanoparticles. Functionalization is possible either
by chemical modification of the isolated particles or by genetic engineering of magnetosome membrane proteins. Genetic approaches involve fusing magnetosome membrane proteins to other enzymes or proteins of interest [72]. Functionalization opens
up a wide range of applications in which magnetosomes bind specifically to cells, proteins, or nucleic acids of interest that are subsequently separated, detected or guided
with magnetic fields [4]. For example, Ginet et al. [73] engineered a nanobiocatalyst