A Trisymmetric Magnetic Microchip Surface for Free and Two‐Way Directional Movement of Magnetic Microbeads

Abstract

it is dominated by the out-of-plane (z) stray component of the magnetic stray field gradient, denoted as dH stray,z /dz, occurring above the magnetised magnetic surface. By alteration of the external magnetic field strength and direction, the occurrence and the position of magnetic field gradients can be varied in a controlled way.Thus, using rotating magnetic fields, the manipulation and transportation of mere and labeled microbeads are realized along defined paths of discrete soft-magnetic patterns. [5][6][7][8][9][10] Similarly, patterned disk arrays are used for the movement of micro particles, [11][12][13][14][15] involving the applications of in-plane and out-of-plane magnetic field sequences. The precise positioning through predefined magnetic tracks [16][17][18][19][20][21] and 2D periodic structures [22] was realized. Moreover, the linear motion of magnetic particles within magnetic tubes [23] was shown. The sorting of microbeads populations in a fixed direction and along a magnetic track on a chip was demonstrated. [24][25][26] In all the latter cases, the particle motion takes place along a predefined axis or direction. A node structure or a switch is necessary in such structures. Limitations in efficiency of movement is another factor that affects the adaptability of magnetic chip based approaches. [27] Overall, using magnetically labeled superparamagnetic beads for selective and free or flexible lateral cell moving together with sorting has not been realized for microfluidic lab-on-chip applications.In this paper, we demonstrate a novel approach for the realization of free lateral and selective motion and, thus, sorting of different ensembles of microbeads by utilizing a broken symmetry in stray field gradients due to symmetrically and asymmetrically applied external magnetic fields. Temporally and spatially tuning of the stray field gradients at corners and along edges in periodically arranged soft-magnetic micromagnets facilitates the individual movement of dissimilar microbead populations. By applying square wave modulated externally applied magnetic field components, we realize the guided motion of microbeads along selectable microcorridors across arrays of magnetic elements. Choosing the proper external magnetic field parameters, we achieve bidirectional propulsion and separation, depending on the size of the microbeads. The areas with 2D periodic structures enable multidirectional and microbead selective transportation of mixed-sized microbead ensembles at a single bead level. The presented dynamical approach of selective bead motion and bead separation paves a new way for the development of alternative magnetic field configurable micromagnetic lab-on-chip devices.The guidance of labeled microcarriers in microfluidic environments is a prerequisite to the development of magnetic pattern assisted lab-on-chip technology. Square wave modulations of in-plane applied magnetic fields enable the forward and backward locomotion of superparamagnetic microspheres on discrete hexagonally arranged ferromagn...

Evaluating and forecasting movement patterns of magnetically driven microbeads in complex geometries

“…3(f), from the sequent halt of the MB one can suggest a significantly higher critical limit of motion. Higher field switching frequencies seem to be accessible and were also shown experimentally 25 .…”

“…The forecast of the trajectory of a MB along a whole array of magnetic elements ( Fig. 1(d)), by using periodic boundary conditions, a periodic array of soft magnetic triangles is demonstrated next 25 . For this more complex magnetic structure, alternatingly switching in-plane applied magnetic fields were used to enable the www.nature.com/scientificreports www.nature.com/scientificreports/ locomotion of MBs along discrete hexagonally arranged ferromagnetic structures.…”

“…In the flowless microfluidic environment the MBs were moved along spatial microcorridors for the positioning and sorting of mixed populations MBs. The ways of motion were depending on the field amplitude, direction, and frequency 25 .…”

Efficient flowless separation of mixed microbead populations on periodic ferromagnetic surface structures

“…[5][6][7] One type of particles are selectively transported across a chip during the immobile response of the other type. [8][9][10][11][12] Multiple particles are simultaneously separated to different directions 12,13 and collected at various locations 6 on a chip. A coexistent control over the motion of multiple type particles is crucial for the efficient separation of target biomolecular entities.…”

“…Yet, the nonreproducible motion of particles and the undesired motion of immobilized particles may result directly in a reduced separation efficiency of the devices. 9,12,13 The particle separation on a magnetic surface is dependent on the mutual magnetic interaction between immobile and moving particles. Furthermore, geometric and magnetic irregularities in the manipulation system may affect the paths of particle motion, causing inefficient separation of mixed particle populations.…”