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.
Highlights
Imaging techniques play a fundamental role in every branch of medicine [1,2,3,4,5,6]
We employed Nuclear Magnetic Resonance (NMR) relaxometry to investigate the dependence of the Magnetic Resonance Imaging (MRI) contrast efficiency on the organic coating of maghemite-based magnetic nanoparticles (MNPs)
We studied MNPs dispersed in water with two different diameters
Summary
Imaging techniques play a fundamental role in every branch of medicine [1,2,3,4,5,6]. Magnetic Resonance Imaging (MRI) has played a leading role, as it combines the possibility of obtaining. MRI requires the development of efficient contrast agents (CAs) (i.e., biocompatible and biodegradable materials properly designed in terms of geometry, interactions with water and magnetic properties) that can be injected into the body to produce an optimized image contrast [8,9,10,11,12,13,14]. Most of them were withdrawn from the market; Resovist® is still sold in a few countries, and Feraheme® is approved for the treatment of iron deficiency in adult chronic kidney disease patients. Superparamagnetic properties (which mainly lead to a reduction of the T2 of the solvent nuclei), low toxicity and the improved synthesis control on the size, shape and surface of the magnetic nanoparticles (MNPs) (due to recently developed synthesis procedures) make them very versatile from an applicative point of view [20]
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