Molecular imaging nanoprobes for theranostic applications.

Effect of Mn doping on hydrolysis of low-temperature synthesized metastable alpha-tricalcium phosphate

Today, magnetic resonance imaging (MRI) is one of the most widely applied noninvasive clinical imaging modalities with excellent applicability in bio- and nanomedicine, particularly in specific detecting and high-quality three-dimensional imaging of tumors/cancers. In this context, the design of efficient nanoscale contrast agents (NCAs) for MRI with high magnetic relaxivity and specificity/selectivity has garnered immense interest deploying a variety of innovatively designed nanostructures. Some important characteristics of NCAs such as biocompatibility, improved relaxivity, high dispersibility, specific targeting, and low toxicity make them ideal candidates for imaging/biosensing applications. The hybridization and surface functionalization/modification of these materials by applying suitable functional groups/agents can help to improve their properties and multifunctionality. However, there is still a long way to go in the clinical applications of these nanoagents to serve as a substitute for Gd-based contrast agents or other commercial materials. Importantly, nanotoxicological and biosafety issues of these NCAs need to be systematically addressed both at pre- and clinical stages; construction of smart multifunctional NCAs with clinical diagnostic and imaging potentials is thus warranted. Herein, recent advancements related to the diagnostic and imaging applications of MRI NCAs are deliberated, focusing on important challenges and future directions. 

Nanoscale Contrast Agents for Magnetic Resonance Imaging: A Review

In developing a cluster-nanocarrier design, as a magnetic resonance imaging contrast agent, we have investigated the enhanced relaxivity of a manganese and iron-oxo cluster grafted within a porous polystyrene nanobead with increased relaxivity due to a higher surface area. The synthesis of the cluster-nanocarrier for the cluster Mn8Fe4O12(O2CC6H4CH═CH2)16(H2O)4, cross-linked with polystyrene (the nanocarrier), under miniemulsion conditions is described. By including a branched hydrophobe, iso-octane, the resulting nanobeads are porous and ∼70 nm in diameter. The increased surface area of the nanobeads compared to nonporous nanobeads leads to an enhancement in relaxivity; r1 increases from 3.8 to 5.2 ± 0.1 mM-1 s-1, and r2 increases from 11.9 to 50.1 ± 4.8 mM-1 s-1, at 9.4 teslas, strengthening the potential for T1 and T2 imaging. Several metrics were used to assess stability, and the porosity produced no reduction in metal stability. Synchrotron X-ray fluorescence microscopy was used to demonstrate that the nanobeads remain intact in vivo. In depth, physicochemical characteristics were determined, including extensive pharmacokinetics, in vivo imaging, and systemic biodistribution analysis.

Paramagnetic Mn8Fe4-co-Polystyrene Nanobeads as a Potential T1-T2 Multimodal Magnetic Resonance Imaging Contrast Agent with In Vivo Studies.

pH-Responsive chitosan-modified gadolinium oxide nanoparticles delivering 5-aminolevulinic acid: A dual cellular and metabolic T1-T2* contrast agent for glioblastoma brain tumors detection

There is an increasing need for gadolinium-free magnetic resonance imaging (MRI) contrast agents, particularly for patients suffering from chronic kidney disease. Using a cluster–nanocarrier combin...

Paramagnetic Clusters of Mn3(O2CCH3)6(Bpy)2 in Polyacrylamide Nanobeads as a New Design Approach to a T1- T2 Multimodal Magnetic Resonance Imaging Contrast Agent.

We have investigated the mechanism of relaxivity for two magnetic resonance imaging contrast agents that both employ a cluster-nanocarrier design. The first system termed Mn8Fe4-coPS comprises the cluster Mn8Fe4O12(L)16(H2O)4 or Mn8Fe4 (1) (L = carboxylate) co-polymerized with polystyrene to form ∼75 nm nanobeads. The second system termed Mn3Bpy-PAm used the cluster Mn3(O2CCH3)6(Bpy)2 or Mn3Bpy (2) where Bpy = 2,2'-bipyridine, entrapped in ∼180 nm polyacrylamide nanobeads. Here, we investigate the rate of water exchange of the two clusters, and corresponding cluster-nanocarriers, in order to elucidate the mechanism of relaxivity in the cluster-nanocarrier. Swift-Connick analysis of O-17 NMR was used to determine the water exchange rates of the clusters and cluster-nanocarriers. We found distinct differences in the water exchange rate between Mn8Fe4 and Mn8Fe4-coPS, and we utilized these differences to elucidate the nanobead structure. Using the transverse relaxivity from O-17 NMR line widths, we were able to determine the hydration state of the Mn3Bpy (2) cluster as well as Mn3Bpy-PAm. Using these hydration states in the Swift-Connick analysis of O-17 NMR, we found the water exchange rate to be extremely close in value for the cluster Mn3Bpy and cluster-nanocarrier Mn3Bpy-PAm.

Trevor Lyons

Papers

Paramagnetic Clusters of Mn3(O2CCH3)6(Bpy)2 in Polyacrylamide Nanobeads as a New Design Approach to a T1- T2 Multimodal Magnetic Resonance Imaging Contrast Agent.

Paramagnetic Mn8Fe4-co-Polystyrene Nanobeads as a Potential T1-T2 Multimodal Magnetic Resonance Imaging Contrast Agent with In Vivo Studies.

Molecular Parameters Promoting High Relaxivity in Cluster-Nanocarrier Magnetic Resonance Imaging Contrast Agents.