## 4 Characterization of Nanomaterials
In an electromagnet-based VSM, a magnetic material is vibrated within a uniform magnetic field H generated by an electromagnet, inducing an electric current in suitably placed sensing coils. The magnetic behavior is regulated in part by the particle size, which may be superparamagnetic. This state is beneficial because it reduces the magnetic attraction and helps to stabilize colloidal suspensions required for biomedical applications. Concerning in vivo studies, nanomaterial circulation time, targeting, and final biodistribution or elimination depend greatly on the particle's size, shape, and superficial properties due to the layer spins on the surface influencing the magnetic behavior. For this quality, biosensing platforms adapt magnetic field sensors to excite the nanoparticles and detect their magnetization [40]. It should be noted that the colloidal stability of nanomaterials is linked to their surface charge, which is due to electrostatic interactions. To understand and characterize these interactions, use has been made of techniques such as isothermal titration calorimetry (ITC), which, by means of thermodynamic parameters, allows for monitoring of the formation of bonds due to the difference in the heat increment in real time [39]. This method allows us to obtain the values of thermodynamic variables such as the binding stoichiometry (n); the binding affinity, which is expressed as an association constant (Ka); and the interaction mechanism, which is explained in terms of binding enthalpy (AH), binding entropy (\(\Delta\)S), and Gibbs free energy (\(\Delta\)G). Finally, this method allows for the identification of the type of interaction from the covalent bond formation to non-covalent interactions such as hydrogen bridges or electrostatic interactions [41]. All characterization techniques provide information regarding the interactions and properties of nanomaterials; they also evaluate the stability and reproducibility of synthesis methods, which allows the processes and formulations of these nanomaterials to be improved. The electrochemical nature of nanomaterials describes a surface phenomenon given by dynamic surfaces and interfaces. In addition, the relation of the surface-volume ratio is associated with the effect on the reactivity of a small cluster when a few atoms on a cluster size change the magnitude order. This change modifies the reactivity and selectivity of nanomaterials and can be regulated by checking the electrochemical performance. The electrochemical characterization techniques are divided into the static method (potentiometric) and dynamic techniques (voltammetry, electro-gravimetric, and cyclic voltametric). The first technique involves a galvanic cell that incorporates a reference electrode, while the dynamic techniques require a net current and a net cell reaction [42]. From the point of view of biological processes, hydrophobicity is considered a property related to protein adsorption, interaction with biological membranes, and the passage of molecules into the interior of a cell. Performing a characterization is fundamental and reflects stability in systems such as emulsions, affinity with other molecules such as proteins, and toxicity of the nanomaterial. To this end, various techniques, such as biphasic partitioning, contact angle measurement, hydrophobic interaction chromatography, and absorption tests, are used [38; 43; 44]. Due to the complexity that exists between organic and inorganic materials, nanomaterials require specific conditioning for their characterization. Many of these techniques are complementary, and their correlation allows for the determination of optimal conditions for the standardization of a nanomaterial synthesis method, as well as the evaluation of these in biological systems.