Magnetic Resonance Imaging (MRI) is a powerful, noninvasive and nondestructive technique, capable of providing three-dimensional (3D) images of living organisms. The use of magnetic contrast agents has allowed clinical researchers and analysts to significantly increase the sensitivity and specificity of MRI, since these agents change the intrinsic properties of the tissues within a living organism, increasing the information present in the images. Advances in nanotechnology and materials science, as well as the research of new magnetic effects, have been the driving forces that are propelling forward the use of magnetic nanostructures as promising alternatives to commercial contrast agents used in MRI. This review discusses the principles associated with the use of contrast agents in MRI, as well as the most recent reports focused on nanostructured contrast agents. The potential applications of gadolinium- (Gd) and manganese- (Mn) based nanomaterials and iron oxide nanoparticles in this imaging technique are discussed as well, from their magnetic behavior to the commonly used materials and nanoarchitectures. Additionally, recent efforts to develop new types of contrast agents based on synthetic antiferromagnetic and high aspect ratio nanostructures are also addressed. Furthermore, the application of these materials in theragnosis, either as contrast agents and controlled drug release systems, contrast agents and thermal therapy materials or contrast agents and radiosensitizers, is also presented.

Magnetic Nanomaterials as Contrast Agents for MRI.

Magnetic nanoparticles are one of the most important and widely used types of nanomaterials, whose unique properties make them special compared to other nanostructures. These particles can be used in various fields. But their role in biomedicine, especially in the field of drug delivery, is significant because their inherent magnetism facilitates many tasks, including targeting, which is very important and necessary in drug delivery. In the present article, an attempt has been made to give general information about magnetic nanoparticles and the properties of particles in biomedical applications. In the following, special attention has been paid to the properties of these particles in drug delivery and their various applications have been studied. The importance of coating magnetic nanoparticles has also been mentioned as a basic requirement for medical applications. In the following, the method of drug loading in magnetic nanoparticles, the entry of particles into the body, targeting, and drug release are discussed, and finally, a brief discussion is presented regarding the pharmacokinetics of drugs and their toxicity in the body.

Magnetic Nanoparticles in Targeted Drug Delivery: a Review

Synergistic adsorption‑photocatalytic degradation of tetracycline by microcrystalline cellulose composite aerogel dopped with montmorillonite hosted methylene blue

Synthesis and Stability of Magnetic Nanoparticles

Nanotechnology offers the possibility of operating on the same scale length at which biological processes occur, allowing to interfere, manipulate or study cellular events in disease or healthy conditions. The development of hybrid nanostructured materials with a high degree of chemical control and complex engineered surface including biological targeting moieties, allows to specifically bind to a single type of molecule for specific detection, signaling or inactivation processes. Magnetite nanostructures with designed composition and properties are the ones that gather most of the designs as theragnostic agents for their versatility, biocompatibility, facile production and good magnetic performance for remote in vitro and in vivo for biomedical applications. Their superparamagnetic behavior below a critical size of 30 nm has allowed the development of magnetic resonance imaging contrast agents or magnetic hyperthermia nanoprobes approved for clinical uses, establishing an inflection point in the field of magnetite based theragnostic agents.

Hybrid Nanostructured Magnetite Nanoparticles: From Bio-Detection and Theragnostics to Regenerative Medicine

Controlling the structure and photocatalytic properties of three—dimensional aerogels obtained by simultaneous reduction and self-assembly of BiOI/GO aqueous colloidal dispersions

Exchange bias (EB) properties have become especially important in hollow magnetic nanoparticles (MNPs) due to the versatility and reduced size of these materials. In this work, we present the synthesis and study of the EB properties of iron-oxide-based hollow MNPs and their precursors Fe/iron oxide MNPs with core/void/shell structure. The two mechanisms involved in EB generation were investigated: the frozen spins present in the nanograins that form the nanoparticles and the surface spins. The effect of external parameters on the coercivity (HC), remanence (MR), exchange bias field (HEB) and frozen spins, such as cooling field (HFC) and temperature, was investigated. Both HC and HEB present a maximum threshold above which their values begin to decrease with HFC, showing a new trend of HEB with HFC and allowing modulation on demand. The existence of surface spins, present on the outer and inner surfaces, was demonstrated, and an intrinsic EB phenomenon (HEB = 444 Oe for hollow iron oxide-based MNPs of 13.1 nm) with significant magnetization (MS~50 emu/g) was obtained. Finally, core/void/shell MNPs of 11.9 nm prior to the formation of the hollow MNPs showed a similar behavior, with non-negligible HEB, highlighting the importance of surface spins in EB generation.

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Significant Surface Spin Effects and Exchange Bias in Iron Oxide-Based Hollow Magnetic Nanoparticles

Iron oxide magnetic nanoparticles (MNPs) have been widely studied due to their versatility for diagnosis, tracking (magnetic resonance imaging (MRI)) and therapeutic (magnetic hyperthermia and drug delivery) applications. In this work, iron oxide MNPs with different single-core (8–40 nm) and multi-core (140–200 nm) structures were synthesized and functionalized by organic and inorganic coating materials, highlighting their ability as magnetic nanotools to boost cell biotechnological procedures. Single core Fe3O4@PDA, Fe3O4@SiO2-FITC-SiO2 and Fe3O4@SiO2-RITC-SiO2 MNPs were functionalized with fluorescent components with emission at different wavelengths, 424 nm (polydopamine), 515 (fluorescein) and 583 nm (rhodamine), and their ability as transfection and imaging agents was explored with HeLa cells. Moreover, different multi-core iron oxide MNPs (Fe3O4@CS, Fe3O4@SiO2 and Fe3O4@Citrate) coated with organic (citrate and chitosan, CS) and inorganic (silica, SiO2) shells were tested as efficient nanoheaters for magnetic hyperthermia applications for mild thermal heating procedures as an alternative to simple structures based on single-core MNPs. This work highlights the multiple abilities offered by the synergy of the use of external magnetic fields applied on MNPs and their application in different biomedical approaches.

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Angela Arnosa Prieto

Papers

Hybrid Nanostructured Magnetite Nanoparticles: From Bio-Detection and Theragnostics to Regenerative Medicine

Controlling the structure and photocatalytic properties of three—dimensional aerogels obtained by simultaneous reduction and self-assembly of BiOI/GO aqueous colloidal dispersions

Significant Surface Spin Effects and Exchange Bias in Iron Oxide-Based Hollow Magnetic Nanoparticles

Fluorescent Single-Core and Multi-Core Nanoprobes as Cell Trackers and Magnetic Nanoheaters