MRI applications, high Ms. magnetic materials that possess superparamagnetism

along with high stability in the biological environment are required. To enhance the

specificity of contrast agents, the surface of the MNPs is modified with functional

group that is specific to the receptor binding site. Wu et al. synthesized porous

carbon-coated magnetite nanoparticles (PCCMNs) by one-pot solvothermal method.

The PCCMNs were later on modified with hyaluronic acid to specifically target

CD44 receptors present on the surface of various cancer cells. Moreover, these

hyaluronic acid modified PCCMNs not only used for in vivo MR imaging and

fluorescent cell imaging but can also act as a drug carrier, and thereby it can provide

a versatile platform for cancer theranostics (Wu et al. 2019). Additionally, Khmara

et al. choose natural polymer chitosan to modify Fe3O4 NPs which not only enhance

the stability of the MNPs but also make the NPs more biocompatible. The authors

demonstrate even after surface modification the MNPs retain their high Ms. and thus

certainly provide strong potential as MRI contrast agent (Khmara et al. 2019).

Similarly, Esmaeili et al. produced dendrimer-like structure on the surface of the

Fe3O4 NPs using (3-aminopropyl)triethoxysilane and polyamidoamine with step-by-

step addition of methyl acrylate and aminosilane in a cycling manner. The

dendrimer-modified MNPs were shown to be nontoxic even at concentration as

high as 100 μg/mL and excellent efficacy for MR imaging and MH applications

(Esmaeili et al. 2019). Xiong et al. produced novel MNPs in which oleic acid-

tailored Fe3O4 NPs were modified with polylactic acid-polyethylene glycol-D-glu-

cosamine (Fe3O4@OA@PLA@PEG@DG), and these were found to exhibit great

potential application as MRI contrast agents for tumor imaging (Xiong et al. 2017).

Cha et al. proposed star polymers that were composed of β-cyclodextrin core and

poly(2-(dimethylamino) ethyl methacrylate arms to be used for surface modification

of Fe3O4 NPs. As compared to linear polymer, star polymers not only strengthen the

MRI signals but also provide stability to the MNPs in the biological environment

(Cha et al. 2017). Atabaev et al. studied the potential of polyethylene glycol-coated

dysprosium-doped Fe3O4 MNPs for MRI applications. A moderate doping with

dysprosium into the Fe3O4 lattice enhanced the magnetization and consequently

improved the sensitivity of MRI signals (Atabaev 2018). Gholibegloo et al. devel-

oped a novel theranostic system composed of cyclodextrin nanosponge polymer

anchored on the surface of Fe3O4 NPs (Fe3O4/CDNS NPs). Further, Fe3O4/CDNS

NPs were modified with folic acid that acts as a targeting agent. Moreover, the system

Fe3O4/CDNS-FA showed selective cytotoxicity and excellent MRI contrast effi-

ciency along with smart drug release capability (Gholibegloo et al. 2019). Arsalani

et al. extracted natural rubber latex (NRL) from Hevea brasiliensis and used it as a

covering agent for Fe3O4 NPs. Magnetization was found to be increased upon

increasing the NRL content in Fe3O4 NPs, and thus NRL can be considered as an

effective natural biocompatible stabilizing agent to be used for improved MRI

applications (Arsalani et al. 2019). Su et al. developed magnetic hybrid composed

of Fe3O4 NPs and Schiff base containing dextran nanogels to be employed for

biomedical applications. Magnetization capability increased dramatically after

encapsulating the Fe3O4 NPs into the dextran nanogels. Results obtained from

MRI studies suggest that the presence of multiple aldehyde groups and Schiff base

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