This paper presents an efficient technique for trapping of magnetic particles in confined spatial locations using customized designs of micro-coils (MCs). Large magnetic field gradients of up to 20 T/mm and large magnetic forces in the range of 10−8 Newton on magnetic particles with diameter of 1 μm have been achieved using MCs with several planar geometrical configurations. A large magnetic field gradient is generated and enhanced by two structural parameters: the small width and high aspect ratio of each single conductor and the ferromagnetic pillars positioned at high-flux density locations. This arrangement creates very steep magnetic potential wells, in particular at the vicinity of the pillars. The system allowed capturing of suspended magnetic particles as far as 1,000 μm from the center of the device. Magnetic particles/cells have been trapped and confined in single and in arrays of deep magnetic potential wells corresponding to the MCs configuration.

Novel magnetic microdevices were developed for magnetic field generation and concentration and successfully characterized and tested for magnetic potential focusing which is very important for various MEMS applications such as magnetic particles manipulation. These microdevices have been fabricated using an innovative processing sequence which eliminates many problems associated with other fabrication techniques and provides a platform for adding other subsequent fabrication steps required to integrate the microcoils with other microcomponents. They consist of high aspect ratio planar coils made of electroplated copper embedded in the silicon substrate, with ferromagnetic pillars and backside plates made of a CoNiP ternary alloy. A large magnetic field gradient is generated and enhanced by two structural parameters: the small width and high aspect ratio of each single conductor and the ferromagnetic pillars positioned at high flux density locations. This arrangement creates very steep magnetic potential wells, in particular at the vicinity of the pillars. The manipulation of micromagnetic particles in a static and continuous flow conditions has been demonstrated.

Cu micro-coils array embedded in the silicon substrate with high aspect ratio conductors for efficient magnetic field generation

Integrated magnetic devices were fabricated, consisting of arrays of microcoils of a novel structure, embedded in a silicon substrate, with small conductors asymmetrically shaped and with ferromagnetic pillars made of a magnetic alloy (NiCoP) as magnetic cores. These structures generated large magnetic field gradients that very effectively attracted magnetic beads. By alternatively injecting currents in an array of such microcoils placed in a microfluidic chamber, magnetic beads were guided in different movement modes and step sizes in a continuous flow.

In this study we present a set of guidelines for the design of current carrying micro-conductors/micro-coils (MCs) for magnetic nanoparticles manipulation in biomedical applications. Precise spatial manipulation requires steep magnetic field gradients and due to the consequences of scaling laws, these gradients should be maximized as the size of the particle reduces. Conventional planar coils have many construction and functional limitations, such as generating only small magnetic field gradients, Joule heating, and limited ability to move particles with high spatial resolution. On the other hand, micro-coils can provide a satisfactory solution to all these problems. The geometrical and structural parameters play significant roles in determining the ability to move guide and transport nanoparticles.Design guidelines were generated from a detailed theoretical treatment and finite element analysis (FEA). The spatial distributions of magnetic fields, field gradients and magnetic forces on particles were simulated using FEA for different geometrical/structural parameters and wire arrangements. An array of wires create a chain of magnetic potential wells that are controllable in terms of magnitude and direction and therefore can be used to control the motion and position of magnetic nano-particles by tuning the current through the array.

This paper reports a comprehensive theoretical, finite element and measurement analysis of different designs of planar micro-electromagnets for bio-molecular manipulation. The magnetic field due to current flowing in complex shapes of current-carrying conductors have been calculated analytically, simulated using finite-element analysis (FEA), and measured using the superconducting quantum interference device technique (SQUID). A comparison of the theoretical and measured magnetic field strength and patterns is presented. The planar electromagnets have been fabricated using patterned Al 2μm thick. The aim of the study is to explore and optimize the geometrical and structural parameters of planar electromagnets that give rise to the highest magnetic fields and forces for magnetic micro-beads manipulation. Magnetic beads are often used in biochemical assays for separation of bio-molecules. Typical beads are 0.2–10μm in diameter and have superparamagnetic properties. Increasing the intensity of the magnetic field generated by a coil by injection a larger current is not the most suitable solution as the maximum current is limited by Joule heating. Consequently, in order to maximize the field for a given current, one should optimize the geometry of the coil, as this is an extremely significant factor in determining the magnetic field intensity in 2D planar designs. The theoretical and measured results of this work show that the meander micro-electromagnet with mesh-shaped winding profile produces the strongest magnetic field (about 2.7μT for a current intensity of 6mA) compared with other meander designs, such as the serpentine and rosette-shaped ones. The magnetic fields of these three types of meander-shaped micro-electromagnets were compared theoretically with that produced by a spiral micro-electromagnet whose technological realization is more complicated and costly due to the fact that it requires an additional insulation layer with a contact window and a second patterned metal layer as a via. Nevertheless, the spiral design produces a much stronger magnetic field up to five times larger than that of the mesh-shaped micro-electromagnet for the same current and electromagnet area. The measured results strongly agree with these conclusions resulted from the theoretical analysis. The results presented in this paper provide a solid and useful basis for the design of a micro-fluidic bio-molecule separation and detection system using magnetic fields and magnetic beads.