Voltage-controlled strain-mediated elliptical micro-magnetic motors for single magnetic bead manipulation

Abstract

Effective manipulation of magnetic beads (MBs) with dimensions similar to single cells is crucial for advancing clinical and diagnostic technologies. Traditional methods like optical tweezers and dielectrophoresis often require complex setups, making them less suitable for scalable laboratory-on-a-chip (LOC) systems. While strain-mediated magnetoelectric (ME) micro-motors offer a promising alternative, they are limited by a 45° rotation when using planar electrode systems, the complexity of multi-electrode systems for rotations beyond 45°, and the lower thermal stability of symmetrical ferromagnetic (FM) rings or disks. This work introduces a ME-based LOC device that incorporates strain-mediated micro-magnetic motors, utilizing shape-anisotropic FM elliptical rings on a ferroelectric substrate to achieve MB rotations up to 90° experimentally with a simple planar electrode system. The inherent high thermal stability of elliptical FM rings enables this rotation without the need for multi-electrode designs. Micromagnetic simulations are employed to identify the optimal elliptical ring structures that generate the localized stray magnetic fields necessary for trapping and rotating MBs. Effective single MB trapping with optimized MB concentrations and flow rates is demonstrated with 40% capture probability. Under an applied electric field of 0.8 MV/m, a 90o rotation is achieved for a 1.5 μm wide elliptical ring, closely aligning with micromagnetic modeling results. The ability to achieve 90° MB rotation without complicated experimental setup opens possibilities for critical biotechnology applications, such as photothermal and hyperthermia therapy, where the thermally stable, highly shape-anisotropic FMs in ME-based LOC devices could be transformative.