Tuned drop-shape magnetophoretic conductors for controlled single-particle transport in microfluidic chips

In recent years, lab-on-a-chip devices have attracted many researchers due to their numerous advantages, making them suitable for important bioapplications. One of the key challenges in this field is manipulating a group of particles and cells at single-particle resolution. Different techniques have been proposed to tackle this challenge; however, none of them offer the controllability and scalability required in most bioapplications. Recently, drop-shape magnetophoretic circuits have been introduced as an advanced technique for the precise transport of a great number of particles simultaneously. However, in moving along the magnetic track, the particles experience a sudden jump from one magnet to the next one, which may not be in a highly controlled fashion and can be problematic. To overcome this issue, in the current work, we introduce a new design equipped with a tuning gate electrode added to the blind spots of the magnetophoretic conductor. This design transports the particles in a tri-axial magnetic field, with a vertical bias field that reduces the attraction force between particles and inhibits the particle cluster formation. We study the effect of straight and curved current-carrying gates and show that they positively affect the resulting magnetic energy. Based on our finite element method, we found the curved gate offers controlled smooth particle transport at lower electrical currents. We fabricate the proposed chip based on this design and show that the experimental results agree well with the simulation predictions. The introduced design enhances the reliability of the magnetophoretic circuits operating in a tri-axial magnetic field and makes them good candidates for fundamental applications in single-cell biology and medicine.