Moderate cooling coprecipitation for extremely small iron oxide as a pH dependent T₁-MRI contrast agent

Abstract

Moderate cooling coprecipitation for monodisperse extremely small iron oxide as a pH dependent T1-MRI contrast agent.

Small iron oxide nanoparticles as MRI T1 contrast agent: scalable inexpensive water-based synthesis using a flow reactor

“…2b). The presence of such ultra-small particles (≤3 nm) at short process times (such as just after initiating the CP) is in line with previous reports on CP synthesis with macromolecules, 26 including dextran. 48,49 The ultra-small particles were identified as crystalline and of the inverse spinel structure (magnetite and/or maghemite) by HRTEM analysis including electron diffraction and zone axis analysis (see Fig.…”

“…1 Iron oxide nanoparticles (IONPs) are a potential substitute, as they are biocompatible with several FDA approved products [2][3][4] and high T 1 values (i.e., long times till the longitudinal magnetisation regrows to its maximum value before an MRI pulse) have been observed for exceedingly small particles. [5][6][7][8] The promising T 1 performance of small IONPs (≤5 nm) is due to their high surface-to-volume ratio increasing the exposure of surface Fe ions to the surrounding water/hydrogen. 6,9,10 In contrast to IONPs used for T 2 contrast enhancement, their performance is not dominated by the high magnetic moment.…”

“…The common method to synthesise small IONPs is the addition of chelating ions 23 or macromolecules such as dextran (which likely yields agglomerates with a reduced surface area), 7,24 frequently in combination with the initiation of CP, i.e., mixing of the precursor and base solution, at high temperatures 25 followed by a controlled cooling. 26,27 Also, fast mixing has been shown to promote the synthesis of small IONPs. [28][29][30] Alternatively, small IONPs for MRI can be produced via rapid (microwave) heating of a FeCl 3 and trisodium citrate solution together with the reducing agent hydrazine.…”

Magnetic Nanomaterials as Contrast Agents for MRI

“…In contrast to Gd-based contrast agents, iron oxide NPs are typically negative, i.e., T 2 , contrast agents (e.g., superparamagnetic iron oxide NPs). Since, these types of contrast agents are associated with background interference and low resolution, several studies have been carried out, leading to the development of ultrasmall iron oxide (USIO) NPs [ 5 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ] and magnetic nanowires (NWs) [ 31 , 36 , 37 , 38 , 39 ]. The T 1 enhancement of USIO-NPs and NWs is associated with increased surface area, suppressed magnetization and surface effects on magnetization.…”

“…In addition, it has been stated that paramagnetic properties can also arise from dimensional confinement. In the regime of a single magnetic domain (i.e., superparamagnetism), when the size of the particle is below a critical value, i.e., typically 5 nm [ 5 , 30 , 31 , 32 , 33 , 34 , 35 ], the magnetization can be easily flipped by the thermal energy. This leads to a T 1 contrast improvement that can be attributed to various aspects, such as the suppression of the magnetization, the increased surface iron center exposure, surface effects and water diffusion [ 40 ].…”