A Hybrid Silica Nanoreactor Framework for Encapsulation of Hollow Manganese Oxide Nanoparticles of Superior T₁ Magnetic Resonance Relaxivity

Abstract

wileyonlinelibrary.comA new hybrid nanoreactor framework with poly(ethylene oxide)-perforated silica walls is designed to encapsulate hollow manganese oxide nanoparticles (MONs) of high distinctness and homogeneity. Achieved by an interfacial templating scheme, the nanoreactor ensures that acidic etching of MONs by an acetate buffer solution is highly controlled for precise control of the hollow interior. As such, hollow MONs with different nanostructures are developed successfully through a facile acetate buffer solution etching. The resultant hollow MONs are integrated within the hybrid nanoreactor and demonstrate superior r 1 relativity of up to 2.58 m M −1 s −1 for T 1 magnetic resonance imaging (MRI). By modifying the nanoreactor architecture, it is also demonstrated that the effi cacy of MONs as T 1 MRI contrast agents can be signifi cantly improved if an optimal cluster of hollow MONs is encapsulated into the hybrid silica framework. The evolution of core morphology with time is studied to elucidate the etching mechanism. It is revealed that the hollow formation arises due to the surface stabilization of MONs by acetate ions and the subsequent acidic etching of the interior core in a sporadic manner. This is different from the commonly reported nanoscale Kirkendall effect or the selective etching of the core-shell MnO/Mn 3 O 4 structure.

Structure–Relaxivity Relationships of Magnetic Nanoparticles for Magnetic Resonance Imaging

“…Meanwhile, diffusion of water molecules was restricted in the mesoporous framework, which contributed to the effective electronic spin relaxation of water protons, namely the geometrical confinement effect. [147] Similar results have also been reported for Mn ions incorporated mesoporous structures, [138c, 148] manganese oxide encapsulated hybrid silica frameworks, [149] and gadolinium-based mesoporous silica complexes. [147,150] Moreover, other materials (e.g., zeolites, titania) were also reported as candidates for fabricating magnetic core-porous shell nanoparticles, providing great opportunities to incorporate new functions and applications.…”

Manganese‐Based Layered Double Hydroxide Nanoparticles as a T1‐MRI Contrast Agent with Ultrasensitive pH Response and High Relaxivity

“…Considering the surface‐exposed Mn(II) ions are predominately responsible for the longitudinal relaxation of surrounding protons, manganese oxide nanoparticles are designed to be highly dispersed on the surface of mesoporous silica with a large specific surface area, in order to increase the amount of exposed Mn(II) ions and finally improve T 1 relaxation. Similarly, a hybrid silica nanoreactor has been designed to encapsulate multiple manganese oxide nanoparticles (≈16 nm) with the well‐defined hollow nanostructure for high‐performance Mn‐based MRI . Indeed, modifying the morphology of manganese oxide nanoparticles has a significant effect on their T 1 ‐relaxation sensitivity to the acidic pH‐triggers.…”

A hybrid system: MnO-incorporated mesoporous silica nanoparticles for theranostic applications

“…According to the SBM theory, correlation time of the NPs is the key variable that governs its relaxivity. Thus, the presence of mesopores (a) allows the anisotropic diffusion of water molecules towards the magnetic core, which is the fastest diffusion occurring along the channels [25], (b) provides a confined environment wherein the motion of the NP is restricted, thereby increasing the interaction between the NPs and water molecules, which is in accordance with the SBM theory [26] and also (c) enhances the inner sphere effect, where the contrast enhancement is due to the interaction between the electrons of the magnetic material and the protons present in the first hydration shell [27]. Furthermore, an increase in the signal intensity with respect to increase in concentration was also observed as reported before [28].…”