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Quantitative magnetometry of ferromagnetic nanorods by microfluidic analytical magnetophoresis



Andrew L. Balk, Lamar O. Mair, Feng Guo, Carlos M. Hangarter, Pramod Mathai, Robert D. McMichael, Samuel M. Stavis, John Unguris


We introduce an implementation of magnetophoresis to measure the absolute magnetization of ferromagnetic nanorods dispersed in fluids, by analyzing the velocity of single nanorods under an applied magnetic field gradient. A microfluidic guideway prevents aggregation of nanorods, isolates them, and confines their motion for analysis. We use a three-dimensional imaging system to precisely track nanorod velocity and particle-surface proximity. We test the effect of the guideway on nanorod velocity under field gradient application, finding that it guides magnetophoresis, but imposes insignificant drag beyond that of a planar surface. This result provides insight into the transport of magnetic nanorods at microstructured interfaces and allows the use of an analytical model to accurately determine the reacted viscous drag in the force balance needed for quantitative magnetometry. We also estimate the confining potential of the guideway with Brownian motion measurements and Boltzmann statistics. We use our technique to measure the magnetization of ferromagnetic nanorods with a noise floor of 8.5 × 10−20 A·m2·Hz−¿. Our technique is quantitative, rapid, and scalable for determining the absolute magnetization of ferromagnetic nanoparticles with high throughput.
Journal of Applied Physics


Nanoparticles, Nanofluidics, Microfluidics, Nanomagnetism


Balk, A. , Mair, L. , Guo, F. , Hangarter, C. , Mathai, P. , McMichael, R. , Stavis, S. and Unguris, J. (2015), Quantitative magnetometry of ferromagnetic nanorods by microfluidic analytical magnetophoresis, Journal of Applied Physics, [online], (Accessed June 22, 2024)


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Created September 3, 2015, Updated November 10, 2018