Configuration and Design of Electromagnets for Rapid and Precise Manipulation of Magnetic Beads in Biosensing Applications

Abstract

Rapid and precise manipulation of magnetic beads on the nano and micro scales is essential in many biosensing applications, such as separating target molecules from background molecules and detecting specific proteins and DNA sequences in plasma. Accurately moving magnetic beads back and forth requires at least two adjustable magnetic field gradients. Unlike permanent magnets, electromagnets are easy to design and can produce strong and adjustable magnetic field gradients without mechanical motion, making them desirable for use in robust and safe medical devices. However, using multiple magnetic field sources to manipulate magnetic beads presents several challenges, including overlapping magnetic fields, added bulk, increased cost, and reduced durability. Here, we provide a thorough analysis, including analytical calculations, numerical simulations, and experimental measurements, of using two electromagnets to manipulate magnetic beads inside a miniature glass cell. We analyze and experimentally demonstrate different aspects of the electromagnets’ design, such as their mutual influence, the advantages and disadvantages of different pole tip geometries, and the correlation between the electromagnets’ positions and the beads’ aggregation during movement. Finally, we have devised a protocol to maximize the magnetic forces acting on magnetic beads in a two-electromagnet setup while minimizing the electromagnets’ size. We used two such electromagnets in a small footprint magnetic modulation biosensing system and detected as little as 13 ng/L of recombinant Zika virus antibodies, which enables detection of Zika IgM antibodies as early as 5 days and as late as 180 days post symptoms onset, significantly extending the number of days that the antibodies are detectable.

Effects of Electromagnets on Bovine Corneal Endothelial Cells Treated with Dendrimer Functionalized Magnetic Nanoparticles

“…Under a magnetic field produced by electromagnets in tapping mode, wound closure in the BCECs treated with 1 μg/mL SPIONs took 10 h. This is even faster than wound closure in the control BCECs. Notably, the magnetic vortex patterns were created by BCECs containing D-SPIONs by applying the magnetic field for both concentrations of D-SPIONs (1 and 10 μg/mL) at different times ( Figure 6 b) [ 38 ].…”

Recent Advances in Rapid and Highly Sensitive Detection of Proteins and Specific DNA Sequences Using a Magnetic Modulation Biosensing System

“…There are several factors affecting the selection of magnetic beads for the experiments. First, the magnetic force acting on the magnetic beads depends on both the magnetic field gradient of the magnetic poles and the beads' magnetic saturation moment [17]. Thus, to rapidly aggregate the beads and shorten the detection time, the magnetic beads used in this research have high magnetic saturation moment.…”

“…The emitted fluorescence is collected by the same optical system and detected by a digital camera equipped with two identical optical emission filters. Two electromagnets on opposite sides of the sample cell apply an alternating magnetic field gradient with a modulation frequency of 1 Hz, which aggregates the beads and transports them in a periodic lateral motion [17]. As the beads with the attached fluorescently labeled probes and target analyte pass in front of the tightly focused laser beam, the resulting emitted fluorescence creates a flashing signal that is easily distinguished from the constant background of the unbound fluorescent molecules.…”

Simultaneous and Independent Micromanipulation of Two Identical Particles with Robotic Electromagnetic Needles

“…Since the particles are free to rotate, the magnetization axis of the particles align with the field vector. Assuming the size of the particle is negligible compared to particle-needle distance and, the magnetic field is sufficiently high that the particle's magnetic moment is saturated, the magnetic force acting on a particle can be simplified as [21];…”