Architectured design of superparamagnetic Fe₃O₄nanoparticles for application as MRI contrast agents: mastering size and magnetism for enhanced relaxivity

Abstract

Graphical AbstractSuperparamagnetic Fe 3 O 4 nanomaterials with enhanced relaxometric properties were prepared by coprecipitation using alkanolamines with different chelating properties. The alkanolamines promoted these achievements by mastering the surface magnetic properties upon size reduction. AbstractThis work reports the mastered design of novel water-dispersible superparamagnetic iron oxide nanomaterials with enhanced magnetic properties and reduced size. A straightforward cost-effective aqueous coprecipitation route was developed, based on the use of three new coprecipitation agents: the polydentate bases diethanolamine, triethanolamine and triisopropanolamine. Through the selection of these alkanolamines which presented different complexing properties, an improvement of the surface spin order could be achieved upon the reduction of the nanomaterial dimensions (from 8.7 to 3.8 nm) owing to the complexation of the polydentate bases with the subcoordinated iron cations on the particle surface. In particular, the alkanolamine with the highest chelating ability (triethanolamine) led to the nanomaterial with the smallest size and the thinnest magnetic "dead" layer.In order to evaluate the importance of the dual control of size and magnetism, the relaxometric properties of the nanomaterials were investigated, whereby maximum values of transverse relaxivity r 2 of 300.30 and 253.92 mM -1 s -1 at 25 and 37 ºC, respectively (at 20 MHz) were achieved, making these nanomaterials potential T 2weighted MRI contrast agents. Moreover, these values were significantly higher than those reported for commercial T 2 contrast agents and other iron oxides with identical dimensions. Hence, we were able to demonstrate that the r 2 enhancement cannot only be achieved by an increase of particle/cluster size, but also through the precise control of the surface magnetic properties while constraining the nanomaterial dimensions. These achievements open new perspectives on the mastered design of magnetic nanoprobes, overcoming the limitations related with the deleterious effect of size reduction. the presence or absence of a hydrophilic capping/coating agent. 12,13 The versatility of this process lies on its cost-effectiveness, eco-sustainability (mild reaction conditions, non-toxic reagents) and scalability. 12-14 Additionally, it offers the possibility of directly obtaining water-dispersible nanomaterials without requiring further treatments, which is of prime importance for biomedical applications. However, the control over the particle

Origin of reduced magnetization and domain formation in small magnetite nanoparticles

“…Single domain particles should have the maximum magnetic moment per volume, which is desirable for their use in ferrofluids12, magnetic separation3, contrast agents45 for magnetic resonance imaging and magnetic hyperthermia67, all of which use iron oxide NPs. However, many researchers observe reduced magnetization, relative to that of the bulk.…”

New MRI contrast agents based on silicon nanotubes loaded with superparamagnetic iron oxide nanoparticles

“…A linear dependence is observed between the inverse proton relaxation times and the iron concentration according to the following equation: $\frac{1}{T_{i,\mathrm{normalobs}}}=\frac{1}{T_{i,0}}+r_i\hspace{0.17em}false[\text{Fe}false],$ where 1/ T i ,obs ( i  = 1, 2) is the inverse relaxation time measured experimentally in the presence of the magnetic nanomaterial, 1/ T i ,0 is the inverse relaxation time of pure water in the absence of the contrast agent, [Fe] is the iron concentration in the contrast agent and r i is the longitudinal ( i  = 1) or transverse ( i  = 2) relaxivity (i.e. proton relaxation rate enhancement per mM Fe cation concentration) [29]. Representative plots are shown in figure 6 for 1/ T 2 versus iron concentration for all Fe 3 O 4 NPs housed within Si NTs.…”

Biopolymer-mediated Green Synthesis of Noble Metal Nanostructures

“…In targeted magnetic resonance imaging (MRI) technique, stabilized gold NPs are conjugated to an active targeting material such as a specific site-targeting carbohydrate [105], peptides [106,109,110], aptamers [108] or external magnetic field-driven iron oxide nanoparticles (IONPs) [111] in order to achieve active site-targeting, detection and better imaging. Superparamagnetic iron oxide nanoparticles (SPIONs) are excellent MRI contrast agents [112,113]. Thus, utilizing stabilized gold-SPION hybrids, such as SPION-gold core-shell, promotes greater improvement of the MRI technique.…”