In situ detection of single micron-sized magnetic beads using magnetic tunnel junction sensors

We have demonstrated the use of highly sensitive magnetic tunnel junction (MTJ) sensors for the detection of individual micron-sized magnetic labels. By integrating the MTJ sensor into a microfluidic channel, we were able to detect the presence of moving superparamagnetic beads (Dynabeads (R) M-280) in real time by direct measurement of the magnetic dipole fields associated with single beads. The dipolar fields of a single bead were sufficient to obtain a signal of 80 m V with signal to noise ratio of 24 dB in an applied field of 15 Oe. Our data show conclusively that MTJ sensors are very promising candidates for future applications involving the accurate detection and identification of biomolecules with magnetic labels. (c) 2005 American Institute of Physics.