**2.3. Charge**

Loading surface and biodistribution of superparamagnetic iron oxide nanoparticles play an important role in the colloidal stability. Surface charging can be described qualitatively by the nature and behavior of surface groups in the solution at a given pH and in the presence of an electrolyte. In terms of quantity, it can be measured as an electric potential in the double layer of the interfacial surface of the nanoparticles found in a suspension state. A high value of zeta potential is an indication of stability in dispersion of superparamagnetic iron oxide nanoparticles due to electrostatic interaction. Composition and structure of nanoparticles are very important for their interaction with biological fluids. In a known environment, superparamagnetic nanoparticle characteristics, such as the chemical composition, both core and neural crest cells, its size and size distribution, shape and angles of curvature, its crystalline structure, smoothness or surface roughness and hydrophobic or hydrophilic levels, are important for their *in vivo* applications. These features can determine their stationary time in the circulatory system [28].

Osaka and his colleagues [29] have reported a correlation between surface charge of magnetite nanoparticles and their cellular absorption efficiency on different cell lines. For example, a superparamagnetic particle with positive charge showed a greater internalization in human breast cancer cells in comparison with those charged negatively, while there was no difference in the degree of internalization in endothelial cells of human umbilical bladder. Thus, the superparamagnetic nanoparticles absorption depends not only on their surface properties but also on cell type.

poly-acid-lactic-co-glycolic, polyethylene glycol, etc. are typical examples of synthetic polymeric systems. Natural polymer coatings include gelatin, dextran, chitosan, etc. The molecules used for stabilization of magnetic nanoparticles must be biocompatible and biodegradable. The most common surfactant molecules are oleic acid, lauric acid, acids, sulfonic acids, alkanes and alkane phosphonates. The surfactants are amphiphilic compounds and they manifest their role at the interface between nanoparticles and solvent. However, magnetic nanoparticles covered with organic compounds, in suspension cannot be used for biological purposes, especially in the delivery of medicines. Changing the surface of nanoparticles post-synthesis is known as core-shell nanoparticles, also used widely. The most commonly used materials are polymers, silica or metals (e.g. gold, cadmium, selenium, silver). Coating materials protect the core against oxidation and therefore keep the magnetic property of nanoparticles. It is known that the iron oxide nanoparticles are non-toxic, but some coating materials may be toxic. For

Preclinical Aspects on Magnetic Iron Oxide Nanoparticles and Their Interventions as Anticancer…

Many researchers have prepared magnetic nanoparticles covered with various surfactants or biomolecules that have been introduced directly in the synthesis process. For example,

using a facile chemical precipitation method. The surfactant was present in the reaction system to improve dispersity. The authors have obtained magnetic nanoparticles with a size range of 25 nm. Liu et al. prepared magnetic nanoparticles coated with chitosan, for the immobilized lipase, using the co-precipitation method. They replaced water with 2% chitosan in acetic acid

Atomic transfer radical polymerization (ATRP) is another common way to cover magnetic nanoparticles, developed by Wang et al. [34]. Due to the magnetic interaction of the iron oxide nanoparticles with biological fluids, the process of formation of free radicals of oxygen reactive species may be increased. To protect the environment *in vivo* from these toxic by-products,

In the past decade, numerous synthesis methods have been developed to obtain M-IONPs. On the basis that the method of preparation plays an essential role in obtaining nanoparticles with tailored properties, the research work regarding the development of new synthesis methods to control the size, shape, morphology and magnetic properties of these nanoparticles is a permanent challenge. In the same time, the synthesis method has to be environmentally friendly, simple, inexpensive and reproducible. Many scientific publications have described efficient synthesis methods, which allow the obtaining of monodisperse magnetic

The synthesis method has to ensure the obtaining of magnetic nanoparticles with specific properties to their application domain by changing the experimental reaction conditions. For biomedical applications, superparamagnetic iron oxide nanoparticles with a specific surface chemistry (for *in vivo* applications), high magnetization values and a narrow size distribution

some materials have been used for biocompatible and rigid coatings, such as gold [28].

O4

nanoparticles covered with octanoic acid

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example, silicon dioxide is biocompatible, but is not biodegradable [28].

Salavati-Niasari et al. [32] have synthesized Fe3

solution during the reaction process [33].

**3. M-IONPs synthesis methods**

nanoparticles, stable for a long time with controlled shape.
