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On-chip Brownian relaxation measurements of magnetic nanobeads in the time domain
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10.1063/1.4811462
/content/aip/journal/jap/113/23/10.1063/1.4811462
http://aip.metastore.ingenta.com/content/aip/journal/jap/113/23/10.1063/1.4811462

Figures

Image of FIG. 1.
FIG. 1.

Schematic of how a magnetic bead relaxes in a flipping magnetic field. The magnetic field changes direction when the current changes direction. Before flipping of the magnetic field, the magnetization of the bead will be parallel with the field. Immediately after flipping of the magnetic field, the magnetization of the bead will be anti-parallel, meaning the magnetization along the applied field is . The bead will then relax by rotation to become parallel with the field ( ).

Image of FIG. 2.
FIG. 2.

Contour plot of the magnetic self-field ( ) from the bias current through the sensor. The black line from m to m represents the sensor. The inset shows a sketch of the sensor, where the red line through the upper left branch represents the cross section where the self-field is calculated.

Image of FIG. 3.
FIG. 3.

Equilibrium values of and obtained from time domain measurements vs. current amplitude . Panel (a) shows corrected equilibrium values of vs. with and without 80 nm magnetic beads. The solid line is a parabolic fit to the measurements with beads. Panel (b) shows values of vs. .

Image of FIG. 4.
FIG. 4.

Brownian relaxation measurements in the time domain. normalized with the fitting parameter vs. time for four different bead sizes. The lines are curve fits of Eq. (15) to the data. The signals have all been corrected for offsets found from fitting.

Image of FIG. 5.
FIG. 5.

Brownian relaxation measurements in the frequency domain. Second harmonic in-phase (top) and out-of-phase (bottom) signal vs. frequency for 5 different bead sizes. The sweep is performed from high to low frequencies. The lines are curve fits of Eq. (19) to the data.

Image of FIG. 6.
FIG. 6.

Time domain measurements of clustering of streptavidin coated bead by binding to bBSA. is plotted vs. time. The lines are curve fits of Eq. (15) to the data.

Image of FIG. 7.
FIG. 7.

Frequency domain measurements of clustering of streptavidin coated beads by bBSA. The in-phase (top) and out-of-phase (bottom) second harmonic sensor signals are plotted vs. bias current frequency. The lines are curve fits of Eq. (19) to the data.

Image of FIG. 8.
FIG. 8.

Median hydrodynamic diameters obtained in the time and frequency domains vs. time after injection. Results are plotted for samples with 0 nM and 10 nM of bBSA.

Tables

Generic image for table
Table I.

Parameters obtained from least squares fitting of Eq. (15) to the time domain measurements and of Eq. (19) to the frequency domain measurements for the four different bead sizes. The 40 nm beads are from Ocean Nanotech and suspended in MilliQ water, while the remaining three types are from Micromod and suspended in PBS. The numbers in parentheses are the errors for the confidence interval obtained from the least squares curve fits.

Generic image for table
Table II.

Parameters obtained from least squares fitting to the measurement in the time and frequency domains for five different bBSA concentrations. The numbers in parentheses are the errors for the confidence interval obtained from the least squares curve fits.

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/content/aip/journal/jap/113/23/10.1063/1.4811462
2013-06-19
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: On-chip Brownian relaxation measurements of magnetic nanobeads in the time domain
http://aip.metastore.ingenta.com/content/aip/journal/jap/113/23/10.1063/1.4811462
10.1063/1.4811462
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