Coating Effect on the 1H—NMR Relaxation Properties of Iron Oxide Magnetic Nanoparticles

Abstract

We present a 1H Nuclear Magnetic Resonance (NMR) relaxometry experimental investigation of two series of magnetic nanoparticles, constituted of a maghemite core with a mean diameter dTEM = 17 ± 2.5 nm and 8 ± 0.4 nm, respectively, and coated with four different negative polyelectrolytes. A full structural, morpho-dimensional and magnetic characterization was performed by means of Transmission Electron Microscopy, Atomic Force Microscopy and DC magnetometry. The magnetization curves showed that the investigated nanoparticles displayed a different approach to the saturation depending on the coatings, the less steep ones being those of the two samples coated with P(MAA-stat-MAPEG), suggesting the possibility of slightly different local magnetic disorders induced by the presence of the various polyelectrolytes on the particles’ surface. For each series, 1H NMR relaxivities were found to depend very slightly on the surface coating. We observed a higher transverse nuclear relaxivity, r2, at all investigated frequencies (10 kHz ≤ νL ≤ 60 MHz) for the larger diameter series, and a very different frequency behavior for the longitudinal nuclear relaxivity, r1, between the two series. In particular, the first one (dTEM = 17 nm) displayed an anomalous increase of r1 toward the lowest frequencies, possibly due to high magnetic anisotropy together with spin disorder effects. The other series (dTEM = 8 nm) displayed a r1 vs. νL behavior that can be described by the Roch’s heuristic model. The fitting procedure provided the distance of the minimum approach and the value of the Néel reversal time (τ ≈ 3.5 ÷ 3.9·10−9 s) at room temperature, confirming the superparamagnetic nature of these compounds.

The effect of size, shape, coating and functionalization on nuclear relaxation properties in iron oxide core–shell nanoparticles: a brief review of the situation

“…62 we studied maghemite superparamagnetic MNPs coated with polyacrylic acid (PAA) and with different core sizes by means of longitudinal nuclear r 1 profiles and transverse nuclear r 2 profiles. This was one of the few cases 53,64,65,67,73 where it was possible to measure r 2 values at ν less than a few MHz, paying attention to the experimental parameters of the measurements, given the peculiarities of fast field cycling (FFC) technology necessary to reach low frequencies: the instability of the acquisition field and the need for refocusing pulses during the FFC relaxation period. MNPs studied in ref.…”

Nanotechnology Advances in the Detection and Treatment of Cancer: An Overview

“…Still, several pre-clinical investigations are already underway to develop different nanoscale therapies 200 , 201 . Iron oxide (maghemite, Fe 2 O 3 ; magnetite, Fe 3 O 4 ) nanomaterials, if their central dimension is 20 nm and smaller, become superparamagnetic at the ambient temperature, allowing around micromolar levels to adjust T 2 relaxation periods and water-related protons to improve the contrast in MRI images 202 . In vivo , SPIONs are often known to have minimal toxic effects as they are assumed to be environmentally friendly; With nanomaterial iron breakdown and its further release into the normal plasma iron stream, it will eventually become integrated into erythrocyte hemoglobin and used for other metabolic pathways 203 , 204 .…”

Effects of PEG Chain Length on Relaxometric Properties of Iron Oxide Nanoparticles-Based MRI Contrast Agent

“…To date, many kinds of materials such as DMSA [ 33 ], PEG [ 34 , 35 , 36 ], PVP [ 37 ], and silica [ 38 , 39 ] have been employed as the surface coating layer of IONPs for MRI applications, among which PEG has shown undoubted advantages in constructing biocompatible probes. Although some efforts have been made to gain insight into the effect of surface chemistry on the contrast properties of IONPs [ 24 , 32 , 40 , 41 ], the influence of surface coating on the relaxivity of the nanoparticles has not been well understood. The particle aggregation, which usually occurs following the surface modification, has troubled researchers to identify the relationship between the relaxometric properties and the surface chemistry of IONPs.…”