Effects of Mesoporous Silica Coating and Postsynthetic Treatment on the Transverse Relaxivity of Iron Oxide Nanoparticles

Abstract

Mesoporous silica nanoparticles have the capacity to load and deliver therapeutic cargo and incorporate imaging modalities, making them prominent candidates for theranostic devices. One of the most widespread imaging agents utilized in this and other theranostic platforms is nanoscale superparamagnetic iron oxide. Although several core-shell magnetic mesoporous silica nanoparticles presented in the literature have provided high T2 contrast in vitro and in vivo, there is ambiguity surrounding which parameters lead to enhanced contrast. Additionally, there is a need to understand the behavior of these imaging agents over time in biologically relevant environments. Herein, we present a systematic analysis of how the transverse relaxivity (r2) of magnetic mesoporous silica nanoparticles is influenced by nanoparticle diameter, iron oxide nanoparticle core synthesis, and the use of a hydrothermal treatment. This work demonstrates that samples which did not undergo a hydrothermal treatment experienced a drop in r2 (75% of original r2 within 8 days of water storage), while samples with hydrothermal treatment maintained roughly the same r2 for over 30 days in water. Our results suggest that iron oxide oxidation is the cause of the r2 loss, and this oxidation can be prevented both during synthesis and storage by the use of deoxygenated conditions during nanoparticle synthesis. The hydrothermal treatment also provides colloidal stability, even in acidic and highly salted solutions, and a resistance against acid degradation of the iron oxide nanoparticle core. The results of this study show the promise of multifunctional mesoporous silica nanoparticles but will also likely inspire further investigation into multiples types of theranostic devices, taking into consideration their behavior over time and in relevant biological environments.

Synthesis and surface functionalization of silica nanoparticles for nanomedicine

“…There are three primary methods that have been investigated to allow for MRI with silica nanoparticles: incorporation of (1) superparamagnetic iron oxide nanoparticles [70–73], (2) gadolinium [74–77], or (3) manganese oxide [78–81]. …”

“…Hurley et al . have characterized the effects of silica coating and post synthetic treatment on the efficacy of SPIONs as a contrast agent [70]. Different silica coatings influence the transverse relaxivity ( r 2 ) of the particles: nonporous silica coatings inherently reduce the interaction of water with the magnetic field of the SPION, which reduces the r 2 value, and therefore a mesoporous coating is preferred.…”

New Approaches to Cryopreservation of Cells, Tissues, and Organs

“…One of the challenges presented by this approach is IONP stability within the strongly ionic environment of CPAs. However, coating the IONPs with mesoporous silica has been shown to improve stability [152, 153]. Moreover, this coating has demonstrated a high stability within biological environments and has maintained that stability within CPAs [154, 155].…”

Formulation Design Facilitates Magnetic Nanoparticle Delivery to Diseased Cells and Tissues

“…PEI attachment onto the MNP surface can be performed by in situ coating, postsynthesis adsorption or grafting [18]. Capitalizing on these properties, PEI was recently used to modify MNPs for successful delivery of nucleic acids [78,79], where MNPs provided magnetic targeting, while PEI condensed the genetic material. These studies also demonstrated that PEI-coated MNPs improved delivery of encapsulated DNA to A549 and B16-F10 tumor cells in the presence of an external magnetic field [79].…”

“…Silica coating of MNPs has been used to reduce oxidation of the magnetic core, which is a primary reason for loss of transverse relaxivity of the particles [78]. The silica shell can protect the metallic core from oxidation under aqueous conditions and silanol groups enable reaction with alcohols to provide stability in nonaqueous media and provide a platform for covalent linkage to numerous specific ligands [85].…”