title: Nanosized corners for trapping and detecting magnetic nanoparticles.
abstract: We present a device concept based on controlled micromagnetic configurations in a corner-shaped permalloy nanostructure terminated with two circular disks, specifically designed for the capture and detection of a small number of magnetic beads in suspension. A transverse head-to-head domain wall (TDW) placed at the corner of the structure plays the role of an attracting pole for magnetic beads. The TDW is annihilated in the terminating disks by applying an appropriate magnetic field, whose value is affected by the presence of beads chemically bound to the surface. In the case where the beads are not chemically bound to the surface, the annihilation of the TDW causes their release into the suspension. The variation of the voltage drop across the corner, due to the anisotropic magnetoresistance (AMR) while sweeping the magnetic field, is used to detect the presence of a chemically bound bead. The device response has been characterized by using both synthetic antiferromagnetic nanoparticles (disks of 70 nm diameter and 20 nm height) and magnetic nanobeads, for different thicknesses of the protective capping layer. We demonstrate the detection down to a single nanoparticle, therefore the device holds the potential for the localization and detection of small numbers of molecules immobilized on the particle's functionalized surface.
authors.affiliation: LNESS-Dipartimento di Fisica, Politecnico di Milano, Via Anzani 42, I-22100 Como, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Donolato
authors.forename: Marco
authors.initials: M
authors.lastname: Gobbi
authors.forename: Paolo
authors.initials: P
authors.lastname: Vavassori
authors.forename: Marco
authors.initials: M
authors.lastname: Leone
authors.forename: Matteo
authors.initials: M
authors.lastname: Cantoni
authors.forename: Vitali
authors.initials: V
authors.lastname: Metlushko
authors.forename: Bojan
authors.initials: B
authors.lastname: Ilic
authors.forename: Mingliang
authors.initials: M
authors.lastname: Zhang
authors.forename: Shan X
authors.initials: SX
authors.lastname: Wang
authors.forename: Riccardo
authors.initials: R
authors.lastname: Bertacco
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry*; D008280:Magnetics; D053768:Metal Nanoparticles / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D036103:Nanotechnology / Q000379:methods*
chemical_list: D005290:Ferric Compounds; C001215:ferrite