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SQUID-Based Bioassay with Magnetic Particles in Flow
M A Espy*, C Carr, J H Sandin, C J Hanson, S G Daniels, A N Matlachov,
S W Graves, M D Ward and R H Kraus, Jr
Los Alamos National Laboratory, Los Alamos, NM 87545, USA
S Fritz and D Leslie-Pelecky
CMRA, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
*corresponding author - espy@lanl.gov
Abstract. We present preliminary results for a magnetic flow spectrometer for magnetic
microparticle separation, and a magnetic flow cytometer for particle identification. The application
of the instrument is to high-throughput bioassay. Here we report on the first application of our
magnetic spectrometer to the sorting of ferromagnetic and superparamagnetic microspheres in flow.
The system is based on a permanent magnet quadrupole and separates the polymer coated magnetic
microspheres based on their magnetic moments. The cryogenic section of our magnetic flow
cytometer, which involves SQUID-based detection of the sorted magnetic microspheres based on
their magnetic moments, has been re-engineered to permit a smaller standoff between the SQUID
array and the flowing magnetic particles. We present preliminary results with the new experimental
setup, with an emphasis on both spatial and signal resolution.
1. Introduction
The goal of bioassay is a highly parallel, high throughput and high sensitivity quantitative molecular
analysis technique that can be used to expand current biomedical research capabilities. The use of
superconducting quantum interference devices (SQUIDs) [1] or fluxgate magnetometers [2] in assay
techniques is now common, with many recent developments utilizing nanoparticle relaxation as a key part
of the process.
In this project we rely on somewhat larger particles (-pm diameter), and do not use the relaxation of
particles, but instead their magnetic moment, M. In the first stage, each particle, which is generally
spherical in shape, is separated into distinct populations defined by their magnetic moment. This is
achieved by flowing the sample through a flow spectrometer that is placed in a quadrupole magnet. The
quadrupole provides a linear magnetic field gradient, which deflects the magnetic microspheres an amount
proportional to their magnetic moments, and the microspheres are then collected in different outlet bins in
populations of similar magnetic moments. The next stage (not reported here) conjugates the magnetic
particles with target molecules and finally, the sample is flown past optical and magnetic sensors, where the
molecule can be identified (by the SQUID) by its magnetic moment.
2. Magnetic Particles
The intended material for our particles was to be samarium cobalt (SmCos), a permanent magnet material
with high coercivity and, more importantly for SQUID-based detection, a very high remanent
magnetisation. Unlike using paramagnetic materials (which are common) the requirement for locating a
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Synchrotron-based high-pressure research in materials science, article, Date Unknown; [Los Alamos, New Mexico]. (https://digital.library.unt.edu/ark:/67531/metadc926359/m1/2/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.