title: Controlled torque on superparamagnetic beads for functional biosensors.
abstract: We demonstrate that a rotating magnetic field can be used to apply a controlled torque on superparamagnetic beads which leads to a tunable bead rotation frequency in fluid. Smooth rotation is obtained for field rotation frequencies many orders of magnitude higher than the bead rotation frequency. A quantitative model is developed, based on results from a comprehensive set of experiments at different field strengths and frequencies. At low frequencies (<10Hz), rotation is due to a small permanent magnetic moment in the bead. At high frequencies (kHz-MHz), the torque results from a phase lag between the applied field and the induced magnetic moment, caused by the non-zero relaxation time of magnetic nanoparticles in the bead. The control of torque and rotation will enable novel functional assays in bead-based biosensors.
authors.affiliation: Eindhoven University of Technology, Eindhoven, The Netherlands.
authors.forename: X J A
authors.initials: XJ
authors.lastname: Janssen
authors.forename: A J
authors.initials: AJ
authors.lastname: Schellekens
authors.forename: K
authors.initials: K
authors.lastname: van Ommering
authors.forename: L J
authors.initials: LJ
authors.lastname: van Ijzendoorn
authors.forename: M W J
authors.initials: MW
authors.lastname: Prins
mesh_terms: D015374:Biosensing Techniques / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D018189:Immunomagnetic Separation / Q000295:instrumentation* / Q000379:methods; D008280:Magnetics / Q000295:instrumentation*; D055617:Micro-Electrical-Mechanical Systems / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D019415:Torque