Quantitative magnetometry of ferromagnetic nanorods by microfluidic analytical magnetophoresis

Published

September 3, 2015

Author(s)

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

Abstract

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.

Citation

Journal of Applied Physics

Volume

118

Issue

9

Pub Type

Journals

Download Paper

https://doi.org/10.1063/1.4929573

Keywords

Nanoparticles, Nanofluidics, Microfluidics, Nanomagnetism

Citation

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], https://doi.org/10.1063/1.4929573 (Accessed October 8, 2025)