Coating Effect on the <sup>1</sup>H—NMR Relaxation Properties of Iron Oxide Magnetic Nanoparticles
Francesca Brero,
Martina Basini,
Matteo Avolio,
Francesco Orsini,
Paolo Arosio,
Claudio Sangregorio,
Claudia Innocenti,
Andrea Guerrini,
Joanna Boucard,
Eléna Ishow,
Marc Lecouvey,
Jérome Fresnais,
Lenaic Lartigue,
Alessandro Lascialfari
Affiliations
Francesca Brero
Dipartimento di Fisica and INFN, Università degli Studi di Pavia, Via Bassi 6, 27100 Pavia, Italy
Martina Basini
Dipartimento di Fisica and INFN, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
Matteo Avolio
Dipartimento di Fisica and INFN, Università degli Studi di Pavia, Via Bassi 6, 27100 Pavia, Italy
Francesco Orsini
Dipartimento di Fisica and INFN, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
Paolo Arosio
Dipartimento di Fisica and INFN, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
Claudio Sangregorio
ICCOM-CNR, via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy
Claudia Innocenti
ICCOM-CNR, via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy
Andrea Guerrini
Dipartimento di Chimica “U. Schiff” and INSTM, Università degli Studi di Firenze, Via della Lastruccia 3-13, 50019 Sesto Fiorentino (FI), Italy
Joanna Boucard
CNRS, CEISAM UMR 6230, Université de Nantes, F-44000 Nantes, France
Eléna Ishow
CNRS, CEISAM UMR 6230, Université de Nantes, F-44000 Nantes, France
Marc Lecouvey
CSPBAT-UMR CNRS 7244, Université Sorbonne Paris Nord, 74 rue Marcel Cachin, 93017 Bobigny, France
Jérome Fresnais
CNRS, Laboratoire de Physico-chimie des Electrolytes et Nanosystèmes Interfaciaux, Sorbonne Université, PHENIX—UMR 8234, CEDEX 05 F-75252 Paris, France
Lenaic Lartigue
CNRS, CEISAM UMR 6230, Université de Nantes, F-44000 Nantes, France
Alessandro Lascialfari
Dipartimento di Fisica and INFN, Università degli Studi di Pavia, Via Bassi 6, 27100 Pavia, Italy
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.