Closed loop microfluidic platform based on domain wall magnetic conduits: a novel tool for biology and medicine
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Closed loop microfluidic platform based on domain wall magnetic conduits: a novel tool for biology and medicine M. Monticelli1, D. Petti1, E. Albisetti1, M. Cantoni1, E. Guerriero1, R. Sordan1, M.Carminati2, G. Ferrari2, M. Sampietro2 and R. Bertacco1 1 CNISM and LNESS - Politecnico di Milano, Via Anzani 42, 22100 Como, Italy 2 Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, P.zza L. Da Vinci 32, 20131 Milano, Italy ABSTRACT In this paper we present an innovative on-chip platform suitable for the simultaneous manipulation and detection of the transit of a single magnetic bead. This system is based on the controlled displacement of constrained magnetic domain walls (DWs) that are used to move and sense particles in suspension over the chip. To this scope, the high stray field from the transverse DWs created at the corners of ferromagnetic zig-zag structures is used for particles manipulation, while electrical contacts flanking a single corner are employed to simultaneously monitor the DW passage through that corner, via anisotropic magneto resistance (AMR) measurements. A single DW carrying a magnetic particle is nucleated and manipulated within the zig-zag shaped magnetic conduit, trough the action of external magnetic fields. At the same time, the variation of the voltage drop across a corner flanked by a pair of electrical leads is measured, allowing to detect the transit of the DW thanks to the change of the relative orientation of current and spins at the corner related to the peculiar micromagnetic configuration of the DW (AMR). Work is in progress in order to selectively distinguish the transit of a naked DW from that of a DW bound to a magnetic particle. This work paves the way to the development of a closed-loop microlfuidic platform for on-chip bead manipulation, where single bead can be finely moved and their motion continuously checked, via AMR electrical detection and without need of optical monitoring, in a fully integrated closed-loop system. INTRODUCTION In the last years the integration of lab on-chip devices with nanoparticles has attracted a growing interest in the field of biology and nanomedicine. In particular, magnetic particles properly functionalized have been employed as labels for cell and molecular manipulation1, drug delivery2 and biosensing3. In the latter case, magnetic particles can be used to sense target molecules at the surface of magnetic sensors where molecular probes are immobilized. Various magnetic sensors based on magnetoresistive effects, such as giant magnetoresistance (GMR)4, tunneling magnetoresistance (TMR)5 and anisotropic magnetoresistance (AMR)6, have been recently developed. The use of the AMR for bead detection in ring shaped sensors has been firstly proposed by Miller et al7. More recently some of the authors demonstrated the possibility to detect the presence of a single magnetic nanoparticle (80 nm diameter), by measuring the AMR signal related to the displacement of a DW between the corners of a Permalloy microsized square ring8
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