A MEMS room-temperature resettable thermomagnetic-track-guided magnetic-bead manipulation integrated with magnetoresistive sensing for bead-motion monitoring

Abstract

In this paper, we report a MEMS room-temperature resettable thermomagnetic-track-guided magnetic-bead manipulation integrated with magnetoresistive sensing for bead-motion monitoring on a silicon wafer. The manipulation/monitoring approach consists of a magnetic bead, a chip (including thermomagnetic NiCu micro-disk tracks, Pt micro heating wires, and Ni magnetoresistive sensing elements, all fabricated on a silicon wafer), pulse-generation circuit, magnetoresistive measuring circuit, thermoelectric generator (TEG), and four external electromagnets. Because Curie temperature of the NiCu micro-disk tracks is in room-temperature range, when a NiCu track is cooled by TEG to lower than the room temperature, the track becomes ferromagnetic and thus is able to attract the bead. When the electromagnets are used to apply magnetic fields to move the bead, the bead motion is guided by the ferromagnetic track. Oppositely, when the heating-wire is used to heat the track higher than the room temperature, the track switches to paramagnetic-like and thus cannot attract the bead. When the magnetic field is applied to move the bead, the bead motion is not-guided by the paramagnetic-like track. By using these approaches, we successfully demonstrated guiding the bead moving around a track and across different tracks. By using magnetoresistive sensing, location of the bead is obtained and consequently monitoring of the bead-motion is achieved. The most important feature is that our approach can easily reset any track anytime during the bead-manipulation in room-temperature range, when comparing to conventional resetting approach which is complicated and requires to several hundred °C. In addition, our approach is the first one to combine the magnetic-track guided magnetic-bead manipulation and magnetoresistive-sensing-element based magnetic-bead motion monitoring on a silicon chip (toward a fully on-chip actuating/sensing MEMS system for magnetic bead manipulation). The results are important and alternative solutions for magnetic-track-guided magnetic bead manipulation for biomedical MEMS.