# Scaling of Transverse Nuclear Magnetic Relaxation due to Magnetic Nanoparticle Aggregation

 dc.contributor.author Brown, Keith A. dc.contributor.author Vassiliou, Christophoros C. dc.contributor.author Issadore, David Aaron dc.contributor.author Berezovsky, Jesse dc.contributor.author Cima, Michael dc.contributor.author Westervelt, Robert M. dc.date.accessioned 2011-12-08T18:29:01Z dc.date.issued 2010 dc.identifier.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. en_US dc.identifier.issn 0304-8853 en_US dc.identifier.uri http://nrs.harvard.edu/urn-3:HUL.InstRepos:5364374 dc.description.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. en_US dc.description.sponsorship Engineering and Applied Sciences en_US dc.language.iso en_US en_US dc.publisher Elsevier en_US dc.relation.isversionof doi:10.1016/j.jmmm.2010.05.044 en_US dash.license OAP dc.subject SPIO en_US dc.subject nuclear magnetic resonance en_US dc.subject T2 shortening en_US dc.subject aggregation en_US dc.subject clustering en_US dc.title Scaling of Transverse Nuclear Magnetic Relaxation due to Magnetic Nanoparticle Aggregation en_US dc.type Journal Article en_US dc.description.version Accepted Manuscript en_US dc.relation.journal Journal of Magnetism and Magnetic Materials en_US dash.depositing.author Westervelt, Robert M. dc.date.available 2011-12-08T18:29:01Z

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