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T. Vemulkar and R. P. Cowburn
The most clinically advanced application involves the use of magnetic nanoparticles as contrast agents in the imaging of biological tissue [17–22]. This encompasses the more established technique of magnetic resonance imaging (MRI) and
the comparatively more recent approach of magnetic particle imaging (MPI) [23].
For therapeutics, the heat generated when magnetic nanoparticles are exposed to
alternating magnetic fields in the 100–1000 kHz range has been harnessed as a cell
killing mechanism [24–29]. By increasing the temperature of the environment near
a concentrated dose of SPIONS in biological tissue such as a tumour for example,
a localized, triggered, tumour destroying therapeutic may be realized. This heat
generation may also be used as the trigger for a thermally sensitive drug delivery
mechanism [24–29].
Magnetic nanoparticles are also used extensively within the biomedical research
space due to the ease of mechanical actuation of magnetic materials. This allows for
their deployment in assays where biomolecules may need to be captured, concentrated, and re-suspended in solution [30, 31]. With the development of extremely
sensitive magnetic field sensors based on magnetoresistance device architectures
[32–34], magnetic nanoparticles may also be used as the detection moiety in
biosensing systems instead of simply as a means of purifying samples for the elution
of analytes. And finally, mechanical actuation has also been used to stimulate cells
and tissue to trigger downstream phenotypic effects [35], as well as trigger cell death
[36] in a different take on the therapeutic approach.
15.1.1 Applications
15.1.1.1 Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is a ubiquitous tool that has given clinicians the
ability to achieve huge improvements in soft tissue contrast, opening a wide array
of diagnostic procedures beyond that offered by X-ray radiation. Rooted firmly in
the principles of nuclear magnetic resonance [37, 38], MRI imaging is based on the
relaxation of the nuclear magnetic spins of hydrogen atoms, present in water and
organic material that comprises human tissue (Fig. 15.1).
Since the inherent variation in signal between tissues is often insufficient for clinical requirements, contrast agents are used to significantly enhance MRI signals by
modifying the values of the characteristic relaxation times, T 1 , T 2, and T 2 * [39–41],
of the nuclear spins in the applied static and dynamic fields of an MRI scanner. T 1
contrast agents work by significantly shortening the T 1 of hydrogen nuclei in their
vicinity, thereby significantly boosting the T 1 positive signal. High-spin paramagnetic ions are typical T 1 contrast agents [42–45], of which Gd
3+ [42, 46, 47] is the
clinical contrast agent of choice when chelated with various organic molecules for
safety. However, significant effort is being expended in to the incorporation of Gd
3+
into nanoparticles [48–51] to increase sensitivity, specificity, and reduce clearance
time and toxicity (particularly nephrotic cystic fibrosis in patients with impaired
T. Vemulkar and R. P. Cowburn
The most clinically advanced application involves the use of magnetic nanoparticles as contrast agents in the imaging of biological tissue [17–22]. This encompasses the more established technique of magnetic resonance imaging (MRI) and
the comparatively more recent approach of magnetic particle imaging (MPI) [23].
For therapeutics, the heat generated when magnetic nanoparticles are exposed to
alternating magnetic fields in the 100–1000 kHz range has been harnessed as a cell
killing mechanism [24–29]. By increasing the temperature of the environment near
a concentrated dose of SPIONS in biological tissue such as a tumour for example,
a localized, triggered, tumour destroying therapeutic may be realized. This heat
generation may also be used as the trigger for a thermally sensitive drug delivery
mechanism [24–29].
Magnetic nanoparticles are also used extensively within the biomedical research
space due to the ease of mechanical actuation of magnetic materials. This allows for
their deployment in assays where biomolecules may need to be captured, concentrated, and re-suspended in solution [30, 31]. With the development of extremely
sensitive magnetic field sensors based on magnetoresistance device architectures
[32–34], magnetic nanoparticles may also be used as the detection moiety in
biosensing systems instead of simply as a means of purifying samples for the elution
of analytes. And finally, mechanical actuation has also been used to stimulate cells
and tissue to trigger downstream phenotypic effects [35], as well as trigger cell death
[36] in a different take on the therapeutic approach.
15.1.1 Applications
15.1.1.1 Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is a ubiquitous tool that has given clinicians the
ability to achieve huge improvements in soft tissue contrast, opening a wide array
of diagnostic procedures beyond that offered by X-ray radiation. Rooted firmly in
the principles of nuclear magnetic resonance [37, 38], MRI imaging is based on the
relaxation of the nuclear magnetic spins of hydrogen atoms, present in water and
organic material that comprises human tissue (Fig. 15.1).
Since the inherent variation in signal between tissues is often insufficient for clinical requirements, contrast agents are used to significantly enhance MRI signals by
modifying the values of the characteristic relaxation times, T 1 , T 2, and T 2 * [39–41],
of the nuclear spins in the applied static and dynamic fields of an MRI scanner. T 1
contrast agents work by significantly shortening the T 1 of hydrogen nuclei in their
vicinity, thereby significantly boosting the T 1 positive signal. High-spin paramagnetic ions are typical T 1 contrast agents [42–45], of which Gd
3+ [42, 46, 47] is the
clinical contrast agent of choice when chelated with various organic molecules for
safety. However, significant effort is being expended in to the incorporation of Gd
3+
into nanoparticles [48–51] to increase sensitivity, specificity, and reduce clearance
time and toxicity (particularly nephrotic cystic fibrosis in patients with impaired