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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) Illustration of coercivity (Hc) tuned bit encoding, where the varied aspect ratios of each bit define unique field values at which the magnetisation reversal occurs; (b) Microscope image of a four-bit microcarrier.
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biosensors-05-00172-f001: (a) Illustration of coercivity (Hc) tuned bit encoding, where the varied aspect ratios of each bit define unique field values at which the magnetisation reversal occurs; (b) Microscope image of a four-bit microcarrier.

Mentions: Previously, we have demonstrated the use of coercivity tuning of magnetic elements for the encoding of suspended microcarriers (or “tags”), providing unique binary codes, by using sequences of applied magnetic field pulses [15]. Figure 1a,b illustrate how the variation of the aspect ratio for each magnetic “bit” determines its coercivity value (Hc) at which the magnetisation reversal (transition between binary states 1 and 0) occurs. This allows for the mass fabrication of nominally-identical tags, where each bit’s state is individually addressable using oscillating external magnetic fields when encoding from the highest to the lowest coercivity value. It has also been demonstrated that these microcarriers can be functionalised on two distinct surfaces (i.e., at the thiol and epoxy groups) with target molecules for bioassay applications [16] and subsequently identified, once positive binding is detected, using in-flow magnetic read-out via an incorporated tunnel magnetoresistance (TMR) sensor [17,18]. We have shown previously [17] that the microcarriers can be detected in a microfluidic channel at flow speeds of 3.6 mm/s at a height of 5 µm above the sensor.


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) Illustration of coercivity (Hc) tuned bit encoding, where the varied aspect ratios of each bit define unique field values at which the magnetisation reversal occurs; (b) Microscope image of a four-bit microcarrier.
© Copyright Policy
Related In: Results  -  Collection

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

biosensors-05-00172-f001: (a) Illustration of coercivity (Hc) tuned bit encoding, where the varied aspect ratios of each bit define unique field values at which the magnetisation reversal occurs; (b) Microscope image of a four-bit microcarrier.
Mentions: Previously, we have demonstrated the use of coercivity tuning of magnetic elements for the encoding of suspended microcarriers (or “tags”), providing unique binary codes, by using sequences of applied magnetic field pulses [15]. Figure 1a,b illustrate how the variation of the aspect ratio for each magnetic “bit” determines its coercivity value (Hc) at which the magnetisation reversal (transition between binary states 1 and 0) occurs. This allows for the mass fabrication of nominally-identical tags, where each bit’s state is individually addressable using oscillating external magnetic fields when encoding from the highest to the lowest coercivity value. It has also been demonstrated that these microcarriers can be functionalised on two distinct surfaces (i.e., at the thiol and epoxy groups) with target molecules for bioassay applications [16] and subsequently identified, once positive binding is detected, using in-flow magnetic read-out via an incorporated tunnel magnetoresistance (TMR) sensor [17,18]. We have shown previously [17] that the microcarriers can be detected in a microfluidic channel at flow speeds of 3.6 mm/s at a height of 5 µm above the sensor.

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