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The Scanning TMR Microscope for Biosensor Applications.

Vyas KN, Love DM, Ionescu A, Llandro J, Kollu P, Mitrelias T, Holmes S, Barnes CH - Biosensors (Basel) (2015)

Bottom Line: We present a novel tunnel magnetoresistance (TMR) scanning microscope set-up capable of quantitatively imaging the magnetic stray field patterns of micron-sized elements in 3D.By incorporating an Anderson loop measurement circuit for impedance matching, we are able to detect magnetoresistance changes of as little as 0.006%/Oe.By 3D rastering a mounted TMR sensor over our magnetic barcodes, we are able to characterize the complex domain structures by displaying the real component, the amplitude and the phase of the sensor's impedance.

View Article: PubMed Central - PubMed

Affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Avenue, CB3-0HE Cambridge, UK. kunalnvyas@gmail.com.

ABSTRACT
We present a novel tunnel magnetoresistance (TMR) scanning microscope set-up capable of quantitatively imaging the magnetic stray field patterns of micron-sized elements in 3D. By incorporating an Anderson loop measurement circuit for impedance matching, we are able to detect magnetoresistance changes of as little as 0.006%/Oe. By 3D rastering a mounted TMR sensor over our magnetic barcodes, we are able to characterize the complex domain structures by displaying the real component, the amplitude and the phase of the sensor's impedance. The modular design, incorporating a TMR sensor with an optical microscope, renders this set-up a versatile platform for studying and imaging immobilised magnetic carriers and barcodes currently employed in biosensor platforms, magnetotactic bacteria and other complex magnetic domain structures of micron-sized entities. The quantitative nature of the instrument and its ability to produce vector maps of magnetic stray fields has the potential to provide significant advantages over other commonly used scanning magnetometry techniques.

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(a) The peak-peak voltage signal observed when measuring the reference through our pre-amplifier. The reference impedance was 20.1 kΩ and the current was ± 1.5 µA. The inset shows the phase difference between the reference and sensor signals as a function of frequency; (b) The percentage change in resistance, ∆R (%), due to an in-plane field is shown in black. The data in red show the same measurement after a sheet of mu-metal is added in between the glass cartridge and the scanner head.
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biosensors-05-00172-f004: (a) The peak-peak voltage signal observed when measuring the reference through our pre-amplifier. The reference impedance was 20.1 kΩ and the current was ± 1.5 µA. The inset shows the phase difference between the reference and sensor signals as a function of frequency; (b) The percentage change in resistance, ∆R (%), due to an in-plane field is shown in black. The data in red show the same measurement after a sheet of mu-metal is added in between the glass cartridge and the scanner head.

Mentions: The frequency response of the pre-amplifier was investigated using the measurement channel with the sensor bypassed. Thus, the output signal, measured after the subtracter, only depends on the reference impedance, which was set to 20.1 kΩ. An AC current with an amplitude of ± 1.5 µA was supplied, and the peak-peak voltage amplitude at the channel output was recorded as a function of frequency using an oscilloscope. The measurement is shown in Figure 4a.


The Scanning TMR Microscope for Biosensor Applications.

Vyas KN, Love DM, Ionescu A, Llandro J, Kollu P, Mitrelias T, Holmes S, Barnes CH - Biosensors (Basel) (2015)

(a) The peak-peak voltage signal observed when measuring the reference through our pre-amplifier. The reference impedance was 20.1 kΩ and the current was ± 1.5 µA. The inset shows the phase difference between the reference and sensor signals as a function of frequency; (b) The percentage change in resistance, ∆R (%), due to an in-plane field is shown in black. The data in red show the same measurement after a sheet of mu-metal is added in between the glass cartridge and the scanner head.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493544&req=5

biosensors-05-00172-f004: (a) The peak-peak voltage signal observed when measuring the reference through our pre-amplifier. The reference impedance was 20.1 kΩ and the current was ± 1.5 µA. The inset shows the phase difference between the reference and sensor signals as a function of frequency; (b) The percentage change in resistance, ∆R (%), due to an in-plane field is shown in black. The data in red show the same measurement after a sheet of mu-metal is added in between the glass cartridge and the scanner head.
Mentions: The frequency response of the pre-amplifier was investigated using the measurement channel with the sensor bypassed. Thus, the output signal, measured after the subtracter, only depends on the reference impedance, which was set to 20.1 kΩ. An AC current with an amplitude of ± 1.5 µA was supplied, and the peak-peak voltage amplitude at the channel output was recorded as a function of frequency using an oscilloscope. The measurement is shown in Figure 4a.

Bottom Line: We present a novel tunnel magnetoresistance (TMR) scanning microscope set-up capable of quantitatively imaging the magnetic stray field patterns of micron-sized elements in 3D.By incorporating an Anderson loop measurement circuit for impedance matching, we are able to detect magnetoresistance changes of as little as 0.006%/Oe.By 3D rastering a mounted TMR sensor over our magnetic barcodes, we are able to characterize the complex domain structures by displaying the real component, the amplitude and the phase of the sensor's impedance.

View Article: PubMed Central - PubMed

Affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Avenue, CB3-0HE Cambridge, UK. kunalnvyas@gmail.com.

ABSTRACT
We present a novel tunnel magnetoresistance (TMR) scanning microscope set-up capable of quantitatively imaging the magnetic stray field patterns of micron-sized elements in 3D. By incorporating an Anderson loop measurement circuit for impedance matching, we are able to detect magnetoresistance changes of as little as 0.006%/Oe. By 3D rastering a mounted TMR sensor over our magnetic barcodes, we are able to characterize the complex domain structures by displaying the real component, the amplitude and the phase of the sensor's impedance. The modular design, incorporating a TMR sensor with an optical microscope, renders this set-up a versatile platform for studying and imaging immobilised magnetic carriers and barcodes currently employed in biosensor platforms, magnetotactic bacteria and other complex magnetic domain structures of micron-sized entities. The quantitative nature of the instrument and its ability to produce vector maps of magnetic stray fields has the potential to provide significant advantages over other commonly used scanning magnetometry techniques.

Show MeSH
Related in: MedlinePlus