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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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Related in: MedlinePlus

(a) Two four-bit tags are scanned in the forward (above) and the reverse (below) directions, showing a high level of reproducibility. The sensitive axis of the TMR sensor points along the length of the magnetic elements. A 10 µm/s scan speed was used with a measurement time-constant of 100 ms. The vertical distance between the sample and sensor is ≈1 µm. It is evident from the stray fields observed that the magnetic elements are not uniformly magnetised, but instead must exhibit ferromagnetic domain structures; (b) Schematic of three characteristic signal shapes, labelled α, β and γ. The corresponding distribution of edge north (N) and south (S) poles are shown along with the possible domain distributions from which these could result.
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biosensors-05-00172-f006: (a) Two four-bit tags are scanned in the forward (above) and the reverse (below) directions, showing a high level of reproducibility. The sensitive axis of the TMR sensor points along the length of the magnetic elements. A 10 µm/s scan speed was used with a measurement time-constant of 100 ms. The vertical distance between the sample and sensor is ≈1 µm. It is evident from the stray fields observed that the magnetic elements are not uniformly magnetised, but instead must exhibit ferromagnetic domain structures; (b) Schematic of three characteristic signal shapes, labelled α, β and γ. The corresponding distribution of edge north (N) and south (S) poles are shown along with the possible domain distributions from which these could result.

Mentions: The stray fields from many of the magnetic elements indicated that the elements do not have a uniform magnetisation at remanence, but instead break down into different ferromagnetic domain configurations. The various kinds of signals observed are all present in the stray field observed from a scan of two four-bit tags shown in Figure 6a. The complexity of the signal observed renders it easy for it to be mistaken for noise; however, the return sweep reproduces the same signal, confirming that we are indeed detecting the magnetic stray field from the two tags in question. Figure 6b shows three schematics of the simplest domain configurations that would give rise to characteristic shapes, as observed from individual magnetic elements. The domain structures are speculative, with only the major pole distributions uniquely identified by our one-dimensional stray field measurement. Three characteristic signal shapes are seen:α


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) Two four-bit tags are scanned in the forward (above) and the reverse (below) directions, showing a high level of reproducibility. The sensitive axis of the TMR sensor points along the length of the magnetic elements. A 10 µm/s scan speed was used with a measurement time-constant of 100 ms. The vertical distance between the sample and sensor is ≈1 µm. It is evident from the stray fields observed that the magnetic elements are not uniformly magnetised, but instead must exhibit ferromagnetic domain structures; (b) Schematic of three characteristic signal shapes, labelled α, β and γ. The corresponding distribution of edge north (N) and south (S) poles are shown along with the possible domain distributions from which these could result.
© Copyright Policy
Related In: Results  -  Collection

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

biosensors-05-00172-f006: (a) Two four-bit tags are scanned in the forward (above) and the reverse (below) directions, showing a high level of reproducibility. The sensitive axis of the TMR sensor points along the length of the magnetic elements. A 10 µm/s scan speed was used with a measurement time-constant of 100 ms. The vertical distance between the sample and sensor is ≈1 µm. It is evident from the stray fields observed that the magnetic elements are not uniformly magnetised, but instead must exhibit ferromagnetic domain structures; (b) Schematic of three characteristic signal shapes, labelled α, β and γ. The corresponding distribution of edge north (N) and south (S) poles are shown along with the possible domain distributions from which these could result.
Mentions: The stray fields from many of the magnetic elements indicated that the elements do not have a uniform magnetisation at remanence, but instead break down into different ferromagnetic domain configurations. The various kinds of signals observed are all present in the stray field observed from a scan of two four-bit tags shown in Figure 6a. The complexity of the signal observed renders it easy for it to be mistaken for noise; however, the return sweep reproduces the same signal, confirming that we are indeed detecting the magnetic stray field from the two tags in question. Figure 6b shows three schematics of the simplest domain configurations that would give rise to characteristic shapes, as observed from individual magnetic elements. The domain structures are speculative, with only the major pole distributions uniquely identified by our one-dimensional stray field measurement. Three characteristic signal shapes are seen:α

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