**6. Conclusions**

SNR. Therefore, the PHE sensor has advantages for more accurate detection of the small

This simple calculation is suitable for the effect of a single bead on the center of small size sensor junction. When the area of the sensor junction is larger than the area of mag‐ netic beads, the calculation must be considered the effect of the magnetic bead from dif‐ ferent positions of sensor junction and the contribution of nearby beads or chains of beads on the sensor. In such a case the output signal changes negative for the bead in‐ side of the sensor junction and changes positive for the beads outside of the junction. Moreover, the signal change does not depend on the number of magnetic beads propor‐ tionally. This was studied systematically and was reported by P.P. Freitas *et al*.,[23], L.

In this part, we design and optimize the planar Hall ring sensor for detecting the hydro‐ dynamic magnetic labels. Once the magnetic labels appear on one arm of the ring sensor, the resistance of the sensor will be changed, the role of resistance change obey the Wheatstone bridge circuit geometry hence the sensor is very sensitive to detect the mag‐

Planar Hall ring sensor was fabricated by photolithography technique. Sensor material Ta(3)/NiFe(10)/IrMn(10)/Ta(3) (nm) was fabricated by using a DC sputtering system with the based pressure of 7×10-8 Torr. The field sensitivity of the ring sensor based on the bilayer thin film was found to be about 0.3 mV.Oe-1. The sensor was integrated with a microfluidic channel, which can produce the laminar flow of the magnetic labels (beads and/or tags) in the specific arms of the ring sensor by hydrodynamic flow focusing technique. This magnet‐ ic platform can detect even a single magnetic bead of 2.8 *µ*m motion in real time by the

The schematic representing the integrated magnetic platform is shown in Fig. 28. In magnetic bead separation experiments initially the magnetic beads with different sizes are injected into the main stream of the microfluidic channel with certain fluidic flow rate. Then the beads are gathered at the weir in the fluid channel and then sorted according to the attractive force exert‐ ed on the magnetic bead by the magnetic elements/magnetic pathways. Therefore, the labeled magnetic beads of same kind will attract to one of the magnetic pathways in the sub channel. The weir at the entrance of the sub-channels opposes the beads temporarily for magnetic beads whose magnetization is insufficient to be attracted by the magnetic elements. But, the beads whose magnetization is sufficient to be attracted by the poles of the saturated ellipses due to the

After successful separation of the magnetic beads of different sizes we wish to adopt two types of different sensing techniques such as an array of PHR biosensors and multi-seg‐ mented nanowires. The planar array of PHR sensor can detect magnetic beads with micron size only. But in case of nanometer size magnetic beads, we wish to use simple read out

stray fields of magnetic beads.

234 State of the Art in Biosensors - General Aspects

netic labels.

Ejsing et al., [9] and Damsgaard *et al*., [45].

**5.4. Integration of magnetic sensors/microfluidic channels**

measurement system with a sampling rate of 5 kHz.

external rotating magnetic field can overcome the weir.

The underlying principle for magnetic biosensing has been elaborately described at first with the examples of different magnetoresistive sensing techniques. Then, the planar Hall resistance sensor has been shown as one of the best sensors for conducting magnetic bead detection experiments. While making an in depth study on the capabilities of a PHR sensor in different configurations and geometries, the sequence of narration ultimately has lead to‐ wards describing the evolution of hybrid AMR and PHR ring sensor in spin-valve configu‐ ration with optimized performance for precise detection of even single magnetic bead. Biofunctionalization experiments were also conducted to ensure that our PHR sensor is ca‐ pable of biomolecule recognition. Therefore, our present sensor can be used to promote for the biomolecular recognition and other molecular interaction detection. This novel planar Hall effect based sensor has been further demonstrated that it can be easily integrated into a lab-on-a-chip and is feasible for bead detection in the sensing current generated magnetic field (without the external applied magnetic field) so as to ensure it an efficient tool for high sensitive biomolecules recognition.

#### **Author details**

Tran Quang Hung1,4, Dong Young Kim2 , B. Parvatheeswara Rao3 and CheolGi Kim1\*

\*Address all correspondence to: cgkim@cnu.ac.kr

1 Department of Materials Science and Engineering, Chungnam National National Universi‐ ty, Daejeon, Korea

2 Department of Physics, Andong National University, Andong, Korea

3 Department of Physics, Andhra University, Visakhapatnam, India

4 Laboratoire Charles Coulomb, CNRS-University Montpellier 2, Montpellier, France

#### **References**


**Author details**

ty, Daejeon, Korea

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\*Address all correspondence to: cgkim@cnu.ac.kr

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