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 |