## 3 Surface Functionalization
Furthermore, magnetic nanoparticles were covered in a core/shell with silica, aminosilane, and a double shell of silica-aminosilane. An ScFv (fragment antibody) and anti-CD73 antibody were attached to the coated nanoparticles to separate the enzyme. The XRD patterns of the analyzed nanoparticles highlight a crystallite size of 12.8 nm, which was similar to the values observed by TEM; this suggested that the magnetite nanoparticles are monocrystalline. TEM images showed an agglomeration of particles with a narrow distribution of 16 \(\pm\) 4 nm. Also, through the FTIR technique, the coating of magnetite with silica was confirmed. Analyzing the magnetization, it was confirmed that the presence of the coating material decreased the magnetization. The magnetic separation of this enzyme with the fragment antibody was found to be 28% higher than for the anti-CD73 antibody, and the enzyme adsorption was improved with the double-shell structures due to the increased length of the polymer chain. Magnetic nanoparticles with a double shell (silica-aminosilane) were also found to be more sensitive than magnetite with a single shell in the detection of biomarkers [127]. Cyclodextrin glycosyltransferase (CGTase) from alkaliophilic _Amphibacillus_ sp. NPST-10 was immobilized on amino-functionalized silica magnetic magnetite nanoparticles to develop a suitable candidate for industrial applications of CGTase, as described by [PERSON] et al. [128]. The XRD patterns analysis revealed that the spinel magnetite has a pure phase of magnetite nanoparticles and TEM images showed broad distribution with a particle size of 50 nm. Furthermore, FTIR measurements confirmed that the coating of magnetite nanoparticles with silica functionalized the nanoparticles with regards to aminopropyl groups. The results have proven significant improvement of the thermal and pH of CGTase upon immobilization. Moreover, the kinetic study showed higher enzyme affinity toward the substrate compared with free CGTase. The immobilized CGTase could retain 87% of its initial activity after five cycles of utilization, indicating that immobilized CGTase on Fe\({}_{3}\)O\({}_{4}\)/NH\({}_{2}\)-SiO\({}_{2}\) has good durability and magnetic recovery. The improvement in kinetic and stability parameters of immobilized CGTase makes the proposed method a suitable candidate for industrial applications of CGTase [128]. Another study proposes an original synthesis method to modify, in one step, core/shell nanoparticles grafted with polymer and functionalized with amino groups. This method presented the PVA cross-linked onto superparamagnetic iron oxide nanoparticles (SPIONs) by the addition of silica precursors with and without amino groups. This study has proven that combining classical silica and amino-functionalized silica precursors at a volume ratio of 3/1 with PVA-coated SPIONs (PVA-SPIONs) allowed for an easier and better synthesis of core/shell silica/SPIONs with PVA covalently grafted onto their surface. In conclusion, precoating oxide nanoparticles with PVA and then using a classical sol-gel route to encapsulate them in silica shells is an interesting and promising method to develop biocompatible nanoparticles for industrialized nanomedicine [129]. The Figure 3 consists of a graphical representation of a surface functionalization model. [PERSON] et al. [130] published a paper aiming to provide insights regarding acidic or basic modified particles that are more effective for enzyme immobilization; therefore, amino (Fe\({}_{3}\)O\({}_{4}\)/SiO\({}_{2}\)/NH\({}_{2}\)) and carboxyl-functionalized (Fe\({}_{3}\)O\({}_{4}\)/SiO\({}_{2}\)/COOH) core-shell Fe\({}_{3}\)O\({}_{4}\)/SiO\({}_{2}\) for L-asparaginase immobilization (ASNase) were prepared. Worth mentioning is that ASNase (EC 3.5.1.1) is an enzyme used effectively in anti-leukemia chemotherapy and is an essential amino acid for cancerous cells, but not for normal cells.