Designing Tripodal and Triangular Gadolinium Oxide Nanoplates and Self-Assembled Nanofibrils as Potential Multimodal Bioimaging Probes

Abstract

Here, we report the shape-controlled synthesis of tripodal and triangular gadolinium oxide (Gd2O3) nanoplates. In the presence of lithium ions, the shape of the nanocrystals is readily controlled by tailoring reaction parameters such as temperature and time. We observe that the morphology transforms from an initial tripodal shape to a triangular shape with increasing reaction time or elevated temperatures. Highly uniform Gd2O3 nanoplates are self-assembled into nanofibril-like liquid-crystalline superlattices with long-range orientational and positional order. In addition, shape-directed self-assemblies are investigated by tailoring the aspect ratio of the arms of the Gd2O3 nanoplates. Due to a strong paramagnetic response, Gd2O3 nanocrystals are excellent candidates for MRI contrast agents and also can be doped with rare-earth ions to form nanophosphors, pointing to their potential in multimodal imaging. In this work, we investigate the MR relaxometry at high magnetic fields (9.4 and 14.1 T) and the optical properties including near-IR to visible upconversion luminescence and X-ray excited optical luminescence of doped Gd2O3 nanoplates. The complex shape of Gd2O3 nanoplates, coupled with their magnetic properties and their ability to phosphoresce under NIR or X-ray excitation which penetrate deep into tissue, makes these nanoplates a promising platform for multimodal imaging in biomedical applications.

Gadolinium‐Doped Iron Oxide Nanoprobe as Multifunctional Bioimaging Agent and Drug Delivery System

“…[ 36,37 ] However, once the ratio of Gd/ Fe exceeded 1/4 to 1/2, the r 1 and r 2 values of GION decreased rapidly to 3.02 × 10 −3 M −1 s −1 and 1.6 × 10 −3 M −1 s −1 , respectively. The r 1 and r 2 values of different Gd/Fe ratios were also summarized in Figure S4 (Supporting Information), indicating that GIONs with 1/4 of Gd/Fe ratio possessed the best MRI performance.…”

Rare Earth Based Anisotropic Nanomaterials: Synthesis, Assembly, and Applications

“…Murray et al reported shapecontrolled synthesis of Gd 2 O 3 tripodal and triangular nanoplates [165]. With an increase of magnetic field strength from 9.4 to 14.1 T, the r 1 of PEI-capped Gd 2 O 3 tripodal nanoplates decreased from 1.41 to 0.89 s −1 mM −1 , and r 2 increased from 140 to 193 s −1 mM −1 .…”

Bottom-Up Synthesis of Nanosized Objects

“…An important point about what we have said so far is that the mechanism of selective adhesion of surfactants to specific facets of nanocrystals is difficult to ascertain from a direct experimental point of view, and most of the evidence so far in favor of this mechanism is deduced from inspection of nanocrystal shapes grown under the various reaction conditions [135,136]. Several quantum chemical calculations on idealized systems however are increasingly supporting such mechanism, at least for CdSe nanocrystals [137][138][139].…”

“…Finally, we need to clarify also that there are many reported cases in which the anisotropic crystal structure is not a key requirement in order to grow shape-controlled nanoparticles. Indeed, several solvothermal routes have been reported so far, which yielded anisotropic shapes for a variety of crystals that are formed in highly symmetrical structures, with no unique axis of symmetry (such as sphalerite, rock salt, or spinel structures, all belonging to cubic space groups) [136,[140][141][142]. In most cases, a "solvent templating" mechanism is invoked, which involves the formation of complexes between the solvent molecules and the ions that will be engulfed into the crystal [140].…”