12 Magnetic Force Microscopy and Magnetic …
293
The magnetic structure of NPs can be also investigated using MFM-based techniques. For instance, Moya et al. used KPFM-MFM to distinguish between ferromagnetic and superparamagnetic nature of NPs in aggregates [55] as well as study
the polarity and reversal mechanism in single magnetic NPs [56].
Finally, other examples of applications of MFM-based techniques for the quantitative evaluation of physical parameters of NPs have been proposed. One of these
applications is in the analysis of core-shell magnetic NPs, which are characterized
by a magnetic (e.g., superparamagnetic) core and a nonmagnetic shell (e.g., gold)
and have been proposed for different applications, e.g., in biomedicine to improve
biocompatibility or to enhance cell internalization [57]. The determination of the
diameter of the magnetic core and of the thickness of the nonmagnetic shell is fundamental in the design of these nanosystems and can be currently addressed for instance
using transmission electron microscopy (TEM). Angeloni et al. [58] have recently
reported preliminary results demonstrating the use of CM-MFM for the evaluation
of core and shell dimensions on individual NPs. Also, using a phenomenological
calibration Dong et al. [59] attempted to evaluate the diameter of magnetic NPs
embedded into vesicular systems which are studied for applications in drug delivery.
Recently, Krivcov at al. [60] demonstrated the capability to indirectly measure size
of magnetite NPs with diameter ranging 10 nm 100 nm embedded in polymer films.
In conclusion, some issues require to be carefully addressed, such as the deletion
of nonmagnetic artifacts, the development of comprehensive models and reliable
experimental methodologies, as well as the need for a certain automatism to allow
the characterization of a statistically significant number of NPs of the investigated
sample with accurate but not too time-consuming procedures. Nonetheless, MFMbased techniques have demonstrated a great potential for the nondestructive quantitative characterization of magnetic properties at the nanoscale, which makes them a
promising metrological tool for magnetic NPs not only in air and at room conditions,
but also in liquid [61] or at low temperature [62].
12.3.2 Detection of Magnetic Nanoparticles in Nano-systems
Magnetic NPs have been proposed for a great number of scientific and technological applications. For instance, in the field of nano-bio-medicine they have been
proposed in applications which can be summarized as theranostic applications, i.e.,
in which selected and functionalized nanomaterials are used as diagnostic materials,
drug delivery vectors, in situ treatment tools, and instrument for the monitoring of
the effectiveness of the treatment. For instance, magnetic NPs have been proposed
in magnetic resonance imaging as nanomaterial-base contrast agents [64], in situ
cancer treatments using hyperthermia [65], or for actively conveying drug delivery
systems through the application of an external magnetic field [50, 66]. Also, magnetic nanocomposites based on the incorporation of magnetic NPs into polymeric
matrices has been proposed for the realization of biocompatible microdevices, e.g.,
for drug release controlled by an external magnetic field. The common denomina-
293
The magnetic structure of NPs can be also investigated using MFM-based techniques. For instance, Moya et al. used KPFM-MFM to distinguish between ferromagnetic and superparamagnetic nature of NPs in aggregates [55] as well as study
the polarity and reversal mechanism in single magnetic NPs [56].
Finally, other examples of applications of MFM-based techniques for the quantitative evaluation of physical parameters of NPs have been proposed. One of these
applications is in the analysis of core-shell magnetic NPs, which are characterized
by a magnetic (e.g., superparamagnetic) core and a nonmagnetic shell (e.g., gold)
and have been proposed for different applications, e.g., in biomedicine to improve
biocompatibility or to enhance cell internalization [57]. The determination of the
diameter of the magnetic core and of the thickness of the nonmagnetic shell is fundamental in the design of these nanosystems and can be currently addressed for instance
using transmission electron microscopy (TEM). Angeloni et al. [58] have recently
reported preliminary results demonstrating the use of CM-MFM for the evaluation
of core and shell dimensions on individual NPs. Also, using a phenomenological
calibration Dong et al. [59] attempted to evaluate the diameter of magnetic NPs
embedded into vesicular systems which are studied for applications in drug delivery.
Recently, Krivcov at al. [60] demonstrated the capability to indirectly measure size
of magnetite NPs with diameter ranging 10 nm 100 nm embedded in polymer films.
In conclusion, some issues require to be carefully addressed, such as the deletion
of nonmagnetic artifacts, the development of comprehensive models and reliable
experimental methodologies, as well as the need for a certain automatism to allow
the characterization of a statistically significant number of NPs of the investigated
sample with accurate but not too time-consuming procedures. Nonetheless, MFMbased techniques have demonstrated a great potential for the nondestructive quantitative characterization of magnetic properties at the nanoscale, which makes them a
promising metrological tool for magnetic NPs not only in air and at room conditions,
but also in liquid [61] or at low temperature [62].
12.3.2 Detection of Magnetic Nanoparticles in Nano-systems
Magnetic NPs have been proposed for a great number of scientific and technological applications. For instance, in the field of nano-bio-medicine they have been
proposed in applications which can be summarized as theranostic applications, i.e.,
in which selected and functionalized nanomaterials are used as diagnostic materials,
drug delivery vectors, in situ treatment tools, and instrument for the monitoring of
the effectiveness of the treatment. For instance, magnetic NPs have been proposed
in magnetic resonance imaging as nanomaterial-base contrast agents [64], in situ
cancer treatments using hyperthermia [65], or for actively conveying drug delivery
systems through the application of an external magnetic field [50, 66]. Also, magnetic nanocomposites based on the incorporation of magnetic NPs into polymeric
matrices has been proposed for the realization of biocompatible microdevices, e.g.,
for drug release controlled by an external magnetic field. The common denomina-