Size-Tunable, Ultrasmall NaGdF₄ Nanoparticles: Insights into their T₁ MRI Contrast Enhancement

High Relaxivities and Strong Vascular Signal Enhancement for NaGdF4 Nanoparticles Designed for Dual MR/Optical Imaging

“…These data obtained with different size and core–shell configurations of UCNPs, indicated that 1) small size is important to reach high longitudinal relaxivities, and 2) the position of Gd 3+ in the crystal affects the relaxometric performance and should be taken into account. van Veggel et al20 recently confirmed the importance of designing ultrasmall NaGdF 4 particles (2.5–8 nm) to achieve high relaxivities ( r 1 = up to 7.2 mM −1 s −1 at 1.5T). However, they also suggested that Gd 3+ ions at the surface of larger particles had a larger contribution to the relaxometric performance than surface Gd 3+ on ultrasmall particles (2.5 nm diam.).…”

“…The interaction of water protons with the unpaired electrons of the Gd 3+ ion similarly accelerates the longitudinal and transverse relaxation of 1 H protons (r 1 , r 2 ), resulting in an increase of signal in T 1 ‐weighted MR images. Indeed, upconverting NaY(Gd)F 4 :Tm 3+ ,Yb 3+ nanoparticles in aqueous media have been found to decrease the relaxation times of water, suggesting the potential use of these nanoparticles as dual optical/MR imaging probes 19–26. Although the optical imaging capacities of these nanoparticles have been well studied,13–15 very limited works have been carried out to achieve a comprehensive understanding of the relaxometric properties of the colloids of the nanoparticle, i.e., from low (<0.5 T), to clinical (0.5 T–3 T), to pre‐clinical (>3 T) magnetic field strengths.…”

Rapid Synthesis of Sub‐10 nm Hexagonal NaYF4‐Based Upconverting Nanoparticles using Therminol® 66

“…Thisr esults in manipulated host lattices, which has ad etrimentale ffect on the luminescent properties of the final materials. [25][26][27][28][29] Other popular strategiest oo btain sub-10 nm UCNPs involve the use of an additional high-boiling solvent such as oleylamine (OM) [30] or trioctylphosphine oxide (TOPO) [31][32][33][34] in the reaction formulation under harsh synthesis conditions (high temperatures and long reaction times), which limits the choice of compatible solvent systemsthat can be used.…”

Small is Smarter: Nano MRI Contrast Agents – Advantages and Recent Achievements

“…After the NPs were transferred into aqueous media by replacing the hydrophobic oleate ligand with polyvinylpyrrolidone, the resulting water soluble particles exhibited clear particle size dependence of r 1 , i.e., smaller NPs show high ionic relaxivity values relative to the larger ones due to larger surface‐to‐volume (S/V) ratio, while the tumbling time increases as the NP size increases, leading to enhanced contribution of surface ions to r 1 . Nevertheless, S/V remains a dominant factor in the above size regime . Gao and coworkers further found out that the particle growth in a similar reaction system undergoes a size broadening process at 300 °C, followed by a size focusing process, which suggests that the Ostwald ripening process plays an important role in determining both particle size and size distribution.…”