Table 2.
The commonly used materials for MNPs functionalization
| Organic compounds | ||
|---|---|---|
| Coating type | Advantages/applications | |
| Monolayers and small molecules | Citrates | Stabilizers MNPs; the free carboxylic groups render a sufficient negative charge on the surface of particles making them hydrophilic |
| Folic acid | Effective tumor targeting agent | |
| Phosphates | Surfactant and stabilizer for nanoparticle dispersion; affords efficient binding ligands on the surface of MNPs | |
| Amines and aminosilanes | Stabilizing agents in the fabrication of various functionalized MNPs; provide -NH2 groups for subsequent functionalization and attaching drugs; used for drug delivery applications | |
| Thiols | Very high binding affinity towards MNPs; used to functionalize MNPs for targeted drug delivery | |
| Macromolecules | Synthetic polymers | |
| Polyethylene glycol (PEG) | Enhances the hydrophilicity and water solubility; provides stability and prevents MNPs agglomeration; PEGylated nanoparticles show a lower cell uptake rate by macrophages, which increases the circulation time in blood; provides -OH groups; used as T1 MRI contrast agents and drug delivery systems | |
| Poli vinyl alcohol (PVA) | Prevents agglomeration, giving rise to monodispersibility | |
| Alginate | Improves the stability and biocompatibility | |
| Natural polymers | ||
| Dextran | Enables optimum polar interactions with iron oxide surfaces, improves the blood circulation time, stability and biocompatibility | |
| Chitosan | Enhances the biocompatibility and stability; provides functional groups: -NH2 and -OH for subsequent functionalization and attaching drugs; hydrophilic; good for drug delivery applications; widely used as non-viral gene delivery system | |
| Starch | Improves the biocompatibility; good for MRI and drug target delivery | |
| Inorganic compounds | ||
| Silica | Enhances the biocompatibility and stability of the nanoparticles; the mesoporous silica coating is biocompatible and offers high controlled porosity; good for drug delivery applications; useful in the fabrication of multifunctional MNPs | |
| Metals | The most popular approach in this category is the conjugation of Fe3O4 with gold because of its biocompatibility and multifunctionality; the final applications are numerous: medical imaging (MRI, CT, PA), radiosensitiation, radiofrequency ablation, biosensing, cell sorting | |
| Metal oxides | Metal oxide (ZnO, TiO2) functionalization has photocatalytic applications | |