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A GMR-based Magnetic Flow Cytometer
Using Matched Filtering
Chih-Cheng Huang, Xiahan Zhou, Da Ying, and Drew A. Hall
University of California, San Diego
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Optical Flow Cytometer
• Quantitative cellular analysis in hematology
• Identifying prognostic indicators:• Cancer, HIV, and other time-dependent biomarkers
• Gold standard for multi-parametric analysis
• Sophisticated instrumentation
Challenge: Hard to translate to a PoC setting!
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Magnetic Flow Cytometer
Signal [mΩ]Blood
SampleMNPs
MNP-coated cells evoke change of sensor resistance
Hz
Optical FCM
• Complex optics, lasers, and
photodetectors
• Extensive sample preparation
• Long turnaround times and
out of reach for routine
monitoring
Magnetic FCM
• Biological samples have no
magnetic background
• Sample preparation can
largely be eliminated
• Can be miniaturized, which
also improves their sensitivity
Optical- vs. Magnetic-FCM
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• Commonly used inside hard disk drives
• Key enabler for higher areal density (larger HDD)
• Nobel prize in 2007 awarded to Fert and Grünberg
Magnetoresistive Sensors
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R.S. Gaster, D.A. Hall, S.X. Wang
nanoLetters 2011 (cover art)
Parallel State
GMR Spin-Valves (GMR SV)
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Bias Point (90˚)
𝑀𝑅 =𝑅𝐴𝑃 − 𝑅𝑃
𝑅𝑃
Parallel (0˚)
Antiparallel (180˚)
D.A. Hall, R.S. Gaster, et al. - Biosensors and Bioelectronics 2010
Hext
Antiparallel State
Micromagnetic Simulations
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5,000× Adembeads
Simulations closely match with our measurement results!
Random distribution of
MNPs on a cell
Hydrodynamic Analysis
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10-8
10-7
10-6
10-5
10-22
10-20
10-18
10-16
10-14
10-12
10-10
10-810
-810
-710
-610
-5
Magnetic force
DLVO force
Gravity
Hydrodynamic force
Langevin force
Magnetic force
Particle diameter (m)
Fo
rce
s (
N)
10-22
10-20
10-18
10-16
10-14
10-12
10-10
10-8
M450
M280MyOne
Adem
Nanomag
SHS30MACS
Matched Filtering
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Improve detection of signal events and reject false alarms
Minimum detectable SNR:14 dB 4.5 dB
Flow Rate Optimization
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0 10 20 30 40 500
10
20
30
40
De
tecte
d E
ve
nts
Pumping rate (L/min)
0 10 20 30 40 500
20
40
60
80
100
120
Ma
xim
um
Sig
na
l (m
)
Pumping rate (L/min)
Tradeoff between signal and flow rate for a given Hz
• Multi-stripe layout: enables distinct magnetic
signature used for matched filtering
• Matched filter: reduces minimum detectable SNR
from 14 dB to 4.5 dB, and improves detection
efficiency
• ToF measurements: offers multi-parametric
analysis of flowing analytes
• GMR-based FCMs: increases portability and rapid
“sample-to-answer” measurement capability
Conclusion
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