Details

Autor(en) / Beteiligte

• Lee, Chiun-Peng
• Lai, Mei-Feng
• Huang, Hao-Ting
• Lin, Chi-Wen
• Wei, Zung-Hang

Titel

Wheatstone bridge giant-magnetoresistance based cell counter

Ist Teil von

• Biosensors & bioelectronics, 2014-07, Vol.57, p.48-53

Ort / Verlag

Kidlington: Elsevier B.V

Erscheinungsjahr

2014

Quelle

MEDLINE

Beschreibungen/Notizen

• A Wheatstone bridge giant magnetoresistance (GMR) biosensor was proposed here for the detection and counting of magnetic cells. The biosensor was made of a top-pinned spin-valve layer structure, and it was integrated with a microchannel possessing the function of hydrodynamic focusing that allowed the cells to flow in series one by one and ensured the accuracy of detection. Through measuring the magnetoresistance variation caused by the stray field of the magnetic cells that flowed through the microchannel above the GMR biosensor, we can not only detect and count the cells but we can also recognize cells with different magnetic moments. In addition, a magnetic field gradient was applied for the separation of different cells into different channels. •In contrast to previous research works that used a single GMR device for biosensing, we used a Wheatstone bridge GMR sensor for detection that is more sensitive than a single GMR sensor. The usage of the Wheatstone bridge can prevent the measurement from being influenced by the noise and signal shift caused by environmental perturbations such as thermal disturbance. This explains why we could easily recognize cells that engulfed different numbers of magnetic nanoparticles. To be more specific, the title of this article has been revised into “Wheatstone bridge giant-magnetoresistance based cell counter”.•We used a lock-in technique in the measurement to single out the signal at a specific reference frequency for a higher signal-to-noise ratio. An alternating external magnetic field was applied to magnetize the magnetic nanoparticles inside the cells, and the reference frequency was fed into a lock-in amplifier to get the phase-sensitive response. Using this approach, the signal-to-noise ratio can be up to 4 without using any filter.•A static bias-field Hy was applied to optimize the sensitivity of the GMR cell counter.•In our proposed cell counting system, the integration of the hydrodynamic focusing function effectively avoided lateral alignment of the flowing cells, that is, each peak in the measured signal corresponded to the crossing of one cell.•Finally, we also demonstrated cell separation function for different magnetic cells. This is very useful for the development of versatile magnetic flow cytometers.