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On the importance of sensor height variation for detection of magnetic labels by magnetoresistive sensors.

Henriksen AD, Wang SX, Hansen MF - Sci Rep (2015)

Bottom Line: We systematically analyze the signal from both a single sensor stripe and an array of sensor stripes as function of the geometrical parameters of the sensor stripes as well as the distribution of magnetic labels over the stripes.We therefore propose a shift of paradigm to maximize the signal due to magnetic labels between sensor stripes.Guidelines for this optimization are provided and illustrated for an experimental case from the literature.

View Article: PubMed Central - PubMed

Affiliation: Department of Micro- and Nanotechnology, Technical University of Denmark, DTU Nanotech, Building 345 East, DK-2800 Kongens Lyngby, Denmark.

ABSTRACT
Magnetoresistive sensors are widely used for biosensing by detecting the signal from magnetic labels bound to a functionalized area that usually covers the entire sensor structure. Magnetic labels magnetized by a homogeneous applied magnetic field weaken and strengthen the applied field when they are over and outside the sensor area, respectively, and the detailed origin of the sensor signal in experimental studies has not been clarified. We systematically analyze the signal from both a single sensor stripe and an array of sensor stripes as function of the geometrical parameters of the sensor stripes as well as the distribution of magnetic labels over the stripes. We show that the signal from sensor stripes with a uniform protective coating, contrary to conventional wisdom in the field, is usually dominated by the contribution from magnetic labels between the sensor stripes rather than by the labels on top of the sensor stripes because these are at a lower height. We therefore propose a shift of paradigm to maximize the signal due to magnetic labels between sensor stripes. Guidelines for this optimization are provided and illustrated for an experimental case from the literature.

No MeSH data available.


(a) The optimal normalized sensor width  found as function of the bead layer height  for an infinite SpBL array. The values obtained for  correspond to 100%. The figure also show the values of w corresponding to 90% and 95%. (b) The gain from using a reduced width, , instead of  for an infinite SpBL array. All calculations were done for .
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f6: (a) The optimal normalized sensor width found as function of the bead layer height for an infinite SpBL array. The values obtained for correspond to 100%. The figure also show the values of w corresponding to 90% and 95%. (b) The gain from using a reduced width, , instead of for an infinite SpBL array. All calculations were done for .

Mentions: Of the sensor widths investigated in Fig. 4c, provided the strongest field in the sensor area. When is reduced, the distance between the magnetic material of adjacent SpBLs decreases and the strength of the magnetic field over a sensor stripe increases. This is analogous to the increase of the magnetic field in an air gap between two magnetic plates when their separation is reduced. However, a smaller gap between the magnets also makes the field more localized near the gap such that the field away from the gap is reduced. Therefore, the width that produces the highest signal for a given SpBL depends on both and such that a small value of is preferred in the near-field limit when is small and a comparatively larger value of is preferred in the far-field limit when is large. This is illustrated in Fig. 6a, where is found by numerical optimization for an infinite SpBL array as function of for . When the bead layer is close to the sensor layer (), the sensor output can be considerably enhanced by reducing . For example, if is reduced from to for , the average magnetic field acting on a sensor stripe is increased by 80% for (Fig. 6b). Further, when the sensor is in line with the SpBL, 〈Hy〉 increases towards M as w decreases towards zero. Figure 6a also shows the curves of that give 90% and 95% of the signal obtained for . These illustrate the impact of changing towards . When both SeBL and SpBL arrays are present, changing towards increases the field from the layer with the lowest value of more than that from the other layer, thus still increasing the overall sensor response.


On the importance of sensor height variation for detection of magnetic labels by magnetoresistive sensors.

Henriksen AD, Wang SX, Hansen MF - Sci Rep (2015)

(a) The optimal normalized sensor width  found as function of the bead layer height  for an infinite SpBL array. The values obtained for  correspond to 100%. The figure also show the values of w corresponding to 90% and 95%. (b) The gain from using a reduced width, , instead of  for an infinite SpBL array. All calculations were done for .
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508666&req=5

f6: (a) The optimal normalized sensor width found as function of the bead layer height for an infinite SpBL array. The values obtained for correspond to 100%. The figure also show the values of w corresponding to 90% and 95%. (b) The gain from using a reduced width, , instead of for an infinite SpBL array. All calculations were done for .
Mentions: Of the sensor widths investigated in Fig. 4c, provided the strongest field in the sensor area. When is reduced, the distance between the magnetic material of adjacent SpBLs decreases and the strength of the magnetic field over a sensor stripe increases. This is analogous to the increase of the magnetic field in an air gap between two magnetic plates when their separation is reduced. However, a smaller gap between the magnets also makes the field more localized near the gap such that the field away from the gap is reduced. Therefore, the width that produces the highest signal for a given SpBL depends on both and such that a small value of is preferred in the near-field limit when is small and a comparatively larger value of is preferred in the far-field limit when is large. This is illustrated in Fig. 6a, where is found by numerical optimization for an infinite SpBL array as function of for . When the bead layer is close to the sensor layer (), the sensor output can be considerably enhanced by reducing . For example, if is reduced from to for , the average magnetic field acting on a sensor stripe is increased by 80% for (Fig. 6b). Further, when the sensor is in line with the SpBL, 〈Hy〉 increases towards M as w decreases towards zero. Figure 6a also shows the curves of that give 90% and 95% of the signal obtained for . These illustrate the impact of changing towards . When both SeBL and SpBL arrays are present, changing towards increases the field from the layer with the lowest value of more than that from the other layer, thus still increasing the overall sensor response.

Bottom Line: We systematically analyze the signal from both a single sensor stripe and an array of sensor stripes as function of the geometrical parameters of the sensor stripes as well as the distribution of magnetic labels over the stripes.We therefore propose a shift of paradigm to maximize the signal due to magnetic labels between sensor stripes.Guidelines for this optimization are provided and illustrated for an experimental case from the literature.

View Article: PubMed Central - PubMed

Affiliation: Department of Micro- and Nanotechnology, Technical University of Denmark, DTU Nanotech, Building 345 East, DK-2800 Kongens Lyngby, Denmark.

ABSTRACT
Magnetoresistive sensors are widely used for biosensing by detecting the signal from magnetic labels bound to a functionalized area that usually covers the entire sensor structure. Magnetic labels magnetized by a homogeneous applied magnetic field weaken and strengthen the applied field when they are over and outside the sensor area, respectively, and the detailed origin of the sensor signal in experimental studies has not been clarified. We systematically analyze the signal from both a single sensor stripe and an array of sensor stripes as function of the geometrical parameters of the sensor stripes as well as the distribution of magnetic labels over the stripes. We show that the signal from sensor stripes with a uniform protective coating, contrary to conventional wisdom in the field, is usually dominated by the contribution from magnetic labels between the sensor stripes rather than by the labels on top of the sensor stripes because these are at a lower height. We therefore propose a shift of paradigm to maximize the signal due to magnetic labels between sensor stripes. Guidelines for this optimization are provided and illustrated for an experimental case from the literature.

No MeSH data available.