**2. Methods of preparation**

Magnetic nanoparticles can be prepared easily by co-precipitation in alkaline aqueous media. Aqueous preparation is preferable to obtain products mean to be used in biomedical applications. Ferrite nanoparticles, both pristine or doped with rare-earth ions can be prepared by the addition of the corresponding Fe(iii), Fe(ii), and rare-earth salt precursors in the oxidation state (iii) [X(iii): Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu], in an appropriate stoichiometry that allows to control the total amount of the rare-earth ions incorporated into the spinel structure, as previously reported [7, 10, 11]. Several rare-earth salts are available as nitrates, halides, or oxides from several commercial sources. Preparation of the rare-earth-doped magnetic nanoparticles can also follow several other modified synthetic procedures reported in the literature [9, 12]. Different types of magnetic ferrites, with a M+2X+3xFe+3 2−xO4 stoichiometry, where M = Zn, Co, Ni, Mn, Cu, can be prepared by selecting the proper amounts of the metal salt precursors. From previous works, superparamagnetic and biocompatible MNPs with strict control in size can be produced by this synthetic methodology (from 8 to 20 nm) [10, 11]. MNPs produced under these conditions are nearly monodisperse (10–15 nm), with zeta potential values higher than −30 mV, low blocking temperatures (*T*B), and high magnetic saturation (*M*s), which make them small enough for internalization into tumors, stable, water-soluble and highly responsive to external magnetic fields, and suitable for biomedical applications. We have also explored recently how the incorporation of rare-earth metals induces not only structural changes but also impacts the magnetic properties, so the novel Ho-containing MNPs will have controlled magnetic and size properties [13, 14].

The surface of the magnetic nanoparticles can be easily modified by coating it with a layer of conveniently selected mesoporous materials (SiO2, carbon, ZnO…). Coating MNPs with a thin layer of silica could be used to produce core-shell

*Designing Magnetic Mesoporous Nanoparticles for Cancer Therapy DOI: http://dx.doi.org/10.5772/intechopen.99973*

**Figure 2.**

nanoparticles with an active surface that can be easily modified and derivatized (**Figure 2**). Once the surface of the MNPs is modified, the functional groups present in the surface could be used to grow another layer mesoporous layer, in order to increase the internal surface required for drug loading or it can be used to attach different chemical functionalities such as bioactive molecules (peptides, amino acids, antibodies, sugars), fluorescent dyes or to immobilize rare-earth ions, useful for radiotherapy or medical imaging.

A second approach for the preparation of MMNPs is to embed the magnetic nanoparticles into them by seeding them during the formation of the mesoporous structure (**Figure 3**). The magnetic nanoparticles could also be trapped into the voids of the mesoporous structure by sonication, stirring, or simple mixing, depending on the affinity among the materials.

After preparation and purification, the products obtained from any of these strategies can be characterized using several analytical techniques such as Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, fluorescence spectroscopy, dynamic light scattering (DLS), thermogravimetric analysis (TGA), powder X-ray diffraction (pXRD), magnetometry, energy dispersive spectroscopy (EDS), BET surface area analysis, and scanning and transmission electron microscopy (SEM and TEM, respectively). Once the magnetic mesoporous nanoparticles have been fully characterized, *in vitro* test of the MMNPs, can be performed using a panel of different cell lines (normal and cancer cells), in order to evaluate their biological activity. There are several methods to determine cell viability, such as the MTT viability assay, which is a quantitative colorimetric assay based on the conversion of MTT to formazan crystals by mitochondrial dehydrogenase. *In vivo* testing in small animal models may give further information on the effectiveness and performance of these MMNPs for cancer treatment, as well as on the toxicology of the nanomaterials. Morphological changes such as cell shrinkage, membrane blebbing, apoptotic body formation, cytoplasmic swelling, and cytopathic effect in cells treated with MMNPs, may be also useful to understand better the mechanisms of the biological interaction among the MMNPs

*Schematic representation of the process for the preparation of core-shell MMNPs.*

### **Figure 3.**

*Schematic representation of the process for preparation of MMNPs where the magnetic nanoparticles were trapped into the mesoporous structure.*

and the cells. Epifluorescence microscopy analysis of the cell cultures, using differentially stained wells with different types of dyes, may also be useful to understand the mechanisms of internalization and cell death.
