外磁场方位及磁珠位置和团聚对巨磁阻生物传感器检测的影响

实现GMR生物传感器对磁珠及其偶联的生物分子的定量检测,必须考虑磁场方位及磁珠位置和磁珠团聚对检测方法的影响。本文首先利用Comsol软件模拟了这3个因素对GMR传感器输出信号的影响,模拟结果表明,外磁场倾斜、磁珠位置偏离电阻条中心和磁珠团聚均会使信号减小,其中外磁场倾斜影响尤甚;当外磁场倾斜为0.5°时,磁珠的信号会减小80%。为了与模拟结果进行比对,制备了与模型相同的线宽为5μm的GMR生物传感器,并测量了输出信号与磁珠覆盖率的关系。测试结果显示,二者呈线性趋势,但与线性关系存在一定程度的偏离。另外,当磁珠覆盖率为23.6%时,实验测得的信号为63μV,比模拟结果的247μV偏小。实验显示这两种偏差均源于前述3个因素对GMR信号的影响。因此,用GMR传感器对磁珠进行定量检测时,为使信号大小与磁珠个数呈线性关系,应保证以下测试条件:外磁场尽可能垂直于传感器平面;测试过程中外磁场倾斜角不能变化;设法使磁珠集中于电阻条中间区域;尽量保证磁珠不团聚。

Influence of orientation of external magnetic field,position and aggregation of magnetic beads on signal of GMR biosensor

To quantitatively measure the number of magnetic beads and their binding biomolecules by a Giant Magnet Resistance(GMR) biosensor, the influences of the orientation of external magnetic field, the positions and the aggregation of magnetic beads on the biosensor signals should be considered. In this paper, the influences of three kinds of factors are simulated using Comsol software and the simulated results show that the signal amplitudes of the biosensor would be reduced by the tilt of external field, the deviation of bead position from the central area of sensor strips, and the aggregation of beads, especial the tilt of external field. When the tilt is 0.5°, the signal will decrease by 80%. Comparing with the simulated results, a GMR biosensor with the width of 5 μm is fabricated. The dependence of signal outputs on the coverage of magnetic beads is measured and results indicate that it is a linear relation with some deviations. Furthermore, the experimental result is 63 μV when the coverage of magnetic beads is 23.6%, which is smaller than the simulated result in 247 μV. Obtained results prove that both kinds of deviations are owing to the three factors. To measure the magnetic beads quantitatively, it suggests that the measuring conditions should be as fellows: making the external magnetic field perpendicular to the sensor plane; keeping the tilt angle unchanged during the measuring process; putting the magnetic beads to concentrate at the central area of the sensor strips; and avoiding the magnetic bead aggregation.