Scaling of Transverse Nuclear Magnetic Relaxation due to Magnetic Nanoparticle Aggregation

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Scaling of Transverse Nuclear Magnetic Relaxation due to Magnetic Nanoparticle Aggregation

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Title: Scaling of Transverse Nuclear Magnetic Relaxation due to Magnetic Nanoparticle Aggregation
Author: Brown, Keith A.; Vassiliou, Christophoros C.; Issadore, David Aaron; Berezovsky, Jesse; Cima, Michael; Westervelt, Robert M.

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Citation: Brown, Keith A., Christophoros C. Vassillou, David Issadore, Jesse Berezovsky, Michael J. Cima, and R. M. Westervelt. 2010. Journal of Magnetism and Magnetic Materials 322(20): 3122-3126.
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Abstract: The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles decreases the transverse nuclear magnetic resonance (NMR) relaxation time \(T_{2}^{CP}\) of adjacent water molecules measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse-echo sequence. This effect is commonly used to measure the concentrations of a variety of small molecules. We perform extensive Monte Carlo simulations of water diffusing around SPIO nanoparticle aggregates to determine the relationship between \(T_{2}^{CP}\) and details of the aggregate. We find that in the motional averaging regime \(T_{2}^{CP}\) scales as a power law with the number \(N\) of nanoparticles in an aggregate. The specific scaling is dependent on the fractal dimension \(d\) of the aggregates. We find \(T_{2}^{CP} \propto N^{-0.44}\) for aggregates with \(d=2.2\), a value typical of diffusion limited aggregation. We also find that in two-nanoparticle systems, \(T_{2}^{CP}\) is strongly dependent on the orientation of the two nanoparticles relative to the external magnetic field, which implies that it may be possible to sense the orientation of a two-nanoparticle aggregate. To optimize the sensitivity of SPIO nanoparticle sensors, we propose that it is best to have aggregates with few nanoparticles, close together, measured with long pulse-echo times.
Published Version: doi:10.1016/j.jmmm.2010.05.044
Terms of Use: This article is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#OAP
Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:5364374

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  • FAS Scholarly Articles [7106]
    Peer reviewed scholarly articles from the Faculty of Arts and Sciences of Harvard University
 
 

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