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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.


The average magnetic field  on the sensor for an infinite SpBL array calculated as function of s/w for zSpBL/w = 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5.Calculations were done for t/w = 0.1.
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f7: The average magnetic field on the sensor for an infinite SpBL array calculated as function of s/w for zSpBL/w = 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5.Calculations were done for t/w = 0.1.

Mentions: For the above situation where w and t are fixed and s and z can be varied, it is more convenient to discuss results normalized to w. Figure 7 shows values of calculated for an infinite SpBL array as function of s/w for the indicated values of zSpBL/w. Figure 7 can be used to understand how s and zSpBL modify the signal. For a fixed value of zSpBL, we observe a steep increase of with s that flattens out when s/w ~ 1 and becomes essentially independent of s for s/w > 2. In this limit, the majority of the magnetic field lines, from the SpBL North face, cross the sensor space to terminate on the South face of the next SpBL and thus only little can be gained by increasing s. Choosing a fixed value of s/w (e.g. s/w = 2 and changing zSpBL/w), we observe that the signal increases strongly for small values of zSpBL > t/2 in agreement with the exponential dependence on zSpBL in Fig. 4. As for z > t/2 the effect of the combined SpBL and SeBL arrays is obtained by subtracting curves for their corresponding z-values. As can be seen in Fig. 7, the difference between curves at different heights is mostly unchanged for s ≥ w; thus when both the SpBL and SeBL arrays are present, s ≥ w is close to optimal and a smaller spacing will decrease sensor signal. Thus only increasing s beyond w is not a feasible approach for reducing towards .


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

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

The average magnetic field  on the sensor for an infinite SpBL array calculated as function of s/w for zSpBL/w = 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5.Calculations were done for t/w = 0.1.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f7: The average magnetic field on the sensor for an infinite SpBL array calculated as function of s/w for zSpBL/w = 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5.Calculations were done for t/w = 0.1.
Mentions: For the above situation where w and t are fixed and s and z can be varied, it is more convenient to discuss results normalized to w. Figure 7 shows values of calculated for an infinite SpBL array as function of s/w for the indicated values of zSpBL/w. Figure 7 can be used to understand how s and zSpBL modify the signal. For a fixed value of zSpBL, we observe a steep increase of with s that flattens out when s/w ~ 1 and becomes essentially independent of s for s/w > 2. In this limit, the majority of the magnetic field lines, from the SpBL North face, cross the sensor space to terminate on the South face of the next SpBL and thus only little can be gained by increasing s. Choosing a fixed value of s/w (e.g. s/w = 2 and changing zSpBL/w), we observe that the signal increases strongly for small values of zSpBL > t/2 in agreement with the exponential dependence on zSpBL in Fig. 4. As for z > t/2 the effect of the combined SpBL and SeBL arrays is obtained by subtracting curves for their corresponding z-values. As can be seen in Fig. 7, the difference between curves at different heights is mostly unchanged for s ≥ w; thus when both the SpBL and SeBL arrays are present, s ≥ w is close to optimal and a smaller spacing will decrease sensor signal. Thus only increasing s beyond w is not a feasible approach for reducing towards .

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.