Magnetophoretic Capacitors Operating in a Tri-Axial Magnetic Field for On-Chip Bioapplications

Lab-on-a-chip devices have been essential in driving the recent advancements in biological research. A major challenge is to precisely manipulate single particles within a group while maintaining the capability to work on a large number of particles. Inspired by the electrical circuits, we introduce capacitors based on drop-shaped magnetic thin films integrated into a microfluidic chip for the first time, enabling the manipulation of particles in a tri-axial rotating magnetic field. The drop-shaped magnetic films in a vertical bias magnetic field lower the attraction force between particles, preventing them from forming undesired clusters. We use both simulations and experiments to investigate the effect of particle size, capacitor geometry, applied magnetic field, and driving frequency on device operation. We combine the proposed magnetophoretic capacitor with magnetophoretic transistors to form an array of single cells paired with barcode-carrying magnetic beads, achieving loading efficiencies higher than 96%. This system allows us to study protein secretion profiles at the single-cell level. We demonstrated the capability of the chip to distinguish cells based on their protein expressions. The proposed design is expandable and potentially plays an important role in single-cell biology and medicine.