Category Archives: Nanoparticles

Single spin magnetic resonance

Wrachtrup, J. and A. Finkler, Single spin magnetic resonance. J Magn Reson, 2016. 269: p. 225-36.

Different approaches have improved the sensitivity of either electron or nuclear magnetic resonance to the single spin level. For optical detection it has essentially become routine to observe a single electron spin or nuclear spin. Typically, the systems in use are carefully designed to allow for single spin detection and manipulation, and of those systems, diamond spin defects rank very high, being so robust that they can be addressed, read out and coherently controlled even under ambient conditions and in a versatile set of nanostructures. This renders them as a new type of sensor, which has been shown to detect single electron and nuclear spins among other quantities like force, pressure and temperature. Adapting pulse sequences from classic NMR and EPR, and combined with high resolution optical microscopy, proximity to the target sample and nanoscale size, the diamond sensors have the potential to constitute a new class of magnetic resonance detectors with single spin sensitivity. As diamond sensors can be operated under ambient conditions, they offer potential application across a multitude of disciplines. Here we review the different existing techniques for magnetic resonance, with a focus on diamond defect spin sensors, showing their potential as versatile sensors for ultra-sensitive magnetic resonance with nanoscale spatial resolution.

Assessment of a Heuristic Model for Characterization of Magnetic Nanoparticles as Contrast Agent in MRI

Félix-González, N., et al., Assessment of a Heuristic Model for Characterization of Magnetic Nanoparticles as Contrast Agent in MRI. Concepts in Magnetic Resonance Part A, 2015. 44A(5): p. 279-286.

In magnetic resonance imaging (MRI), the use of magnetic nanoparticles (MNPs) as contrast agent (CA) greatly enhances the possibility to identify several diseases hardly diagnosed by other means. The efficacy of a new CA is described by the longitudinal and transverse relaxivity. Nuclear Magnetic Relaxation Dispersion (NMRD) profiles represent the evolution of relaxivities with magnetic field. Many efforts have been taken to develop theoretical models to depict water proton relaxation in presence of magnetic compounds. The use of theoretical models in junction with NMRD profiles has become a powerful tool to characterize MNPs as CA. In this work, a heuristical theoretical model was implemented, verified and assessed with different magnetic materials. It has been demonstrated that the model works well when using iron cores but fails with other magnetic compounds. A weighting factor associated with Langevin function was introduced to the model. This extra calibration enables the model to be used with other magnetic compounds to characterize new CAs in MRI.

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