Detection of single magnetic bead using InAs micro-Hall sensors for biological applications

We have fabricated and characterized micro-Hall sensors from InAs/AlSb quantum well heterostructures containing a two-dimensional electron gas. The sensors exhibit room temperature field sensitivities as high as 600 $\Omega $/T, mobilities $>$2$\times $10$^{4}$ cm$^{2}$/V$\cdot $s and low 1/f noise which result in an average field resolution down to the sub- gauss range. Measurements were carried out at temperatures below 150 K on a single submicron superparamagnetic bead (d$\sim $0.9 $\mu $m) that are intended to be used as magnetic labels in biological applications [1]. The magnetization showed expected Langevin behavior as a function of applied field with good signal to noise ratio, demonstrating good potential for the sensors to be used as a detection tool in biological applications. We have also measured the magnetic hysteresis for a single ferromagnetic Ni nanowire (d $\sim $ 200nm) using the device. Our ongoing efforts to demonstrate room temperature operation and to develop biocompatible detection schemes utilizing the micro-Hall sensors will be presented. This work was supported by NSF NIRT Grant ECS-0210332 [1] Q. A. Pankhurst et al., J. Phys. D \textbf{36 }R167 (2003) .