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. 2022 Jun 27;20:305. doi: 10.1186/s12951-022-01510-w

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