Abstract
The relaxometric properties of ultrasmall Gd2O3 nanoparticles coated with various ligands were investigated. These ligands include small diacids with hydrophobic chains, namely, succinic acid (Mw = 118.09 amu), glutaric acid (Mw = 132.12 amu), and terephthalic acid (Mw = 166.13 amu), and large polyethylenimines (PEIs) with hydrophilic chains, namely, PEI-1300 (M¯n=1300) and PEI-10000 (M¯n=10000). Ligand-size and ligand-chain hydrophilicity effects were observed. The longitudinal (r1) and transverse (r2) water proton relaxivities generally decreased with increasing ligand-size (the ligand-size effect). The ligand-size effect was weaker for PEI because its hydrophilic chains allow water molecules to access the nanoparticle (the ligand-chain hydrophilicity effect). This result was explained on the basis of the magnetic dipole interaction between the dipoles of the nanoparticle and water proton. In addition, all samples were found to be non-toxic in cellular cytotoxicity tests.
Highlights
INTRODUCTIONBecause of their high density of Gd per nanoparticle and high surface-to-volume ratio, ultrasmall Gd2O3 nanoparticles have shown higher longitudinal water proton relaxivities (r1 values) than conventional Gd-chelates and are considered potential T1 magnetic resonance imaging (MRI) contrast agents.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18] The studies conducted so far have investigated the relaxometric properties, surface functionalizations, and in vivo MR images of Gd2O3 nanoparticles.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18] A particle-size effect on the relaxometric properties of lanthanide oxide nanoparticles has been reported.[1,17,19] the effects of ligands on the relaxometric properties of ultrasmall Gd2O3 nanoparticles have rarely been studied
The relaxometric properties of ultrasmall Gd2O3 nanoparticles coated with various ligands were investigated
It is important to note that the accessibility of water molecules to the ultrasmall Gd2O3 nanoparticle is the principal factor affecting the enhancement of the water proton relaxation
Summary
Because of their high density of Gd per nanoparticle and high surface-to-volume ratio, ultrasmall Gd2O3 nanoparticles have shown higher longitudinal water proton relaxivities (r1 values) than conventional Gd-chelates and are considered potential T1 magnetic resonance imaging (MRI) contrast agents.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18] The studies conducted so far have investigated the relaxometric properties, surface functionalizations, and in vivo MR images of Gd2O3 nanoparticles.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18] A particle-size effect on the relaxometric properties of lanthanide oxide nanoparticles has been reported.[1,17,19] the effects of ligands on the relaxometric properties of ultrasmall Gd2O3 nanoparticles have rarely been studied. The transverse (or T2) water proton spin relaxation is mainly induced by the interaction of the water proton spin with the fluctuating local magnetic field generated by the total nanoparticle magnetic moment of the contrast agent (that is, the magnetic moment arising from both the spin and orbital motions of the electrons of the metals contributes to the T2 relaxation).[19,21,22,23] ultrasmall Gd2O3 nanoparticles can contribute to both the T1 and T2 relaxations because Gd3+ has a pure spin of 7/2 arising from its 7 unpaired 4f-electrons, which is the largest pure spin in the periodic table Based on this fact and using a simple magnetic dipole interaction model, two types of ligand effects are addressed in this study. In vitro cytotoxicity tests were performed to confirm the biocompatibility of ligand-coated ultrasmall Gd2O3 nanoparticles
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