Kinematic study of motile microalgae under the influence of low gradient magnetic field
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Date
2018-08-01
Authors
Ng Wei Ming
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Abstract
Magnetic microbead composed of a polystyrene (PS) core, iron oxide nanoparticles (IONPs) and cationic polyelectrolyte, was prepared via layer-by-layer assembly. The IONPs were synthesized by co-precipitation method. The successful deposition of IONPs followed by polyelectrolyte onto the PS bead was monitored with electrophoretic mobility measurement. The core-shell morphology of the magnetic microbead was confirmed by transmission electron microscopy technique, and its magnetic mass and magnetic property was determined by using atomic absorption spectroscopy and vibrating sample magnetometer respectively. An artificial magnetotactic microbot was created by attaching a magnetic microbead onto a microalgal cell by the means of electrostatic interaction. The kinematic behaviors of the microbots carrying magnetic microbeads of two different sizes, with diameter of 2 μm and 4.5 μm, in the absence and the presence of low gradient magnetic field (∇𝐵<100 T/m) were characterized. In the absence of magnetic field, the microbot exhibited a helical motion as a result of the misalignment between its thrust force and the symmetry axis after the attachment. The microbot bound with a larger magnetic microbead moved with higher translational velocity but rotated slower about its axis of rotation. The viscous force was balanced by the thrust force of the microbot, resulting in a randomized swimming behavior of the microbot at its terminal velocity. Meanwhile, under the influence of a low gradient magnetic field, the directional control of the microbot was achieved based on following the principles: (1) magnetophoretic force was insignificant on influencing its perpendicular motion, and, (2) its parallel motion was dependent on both self-swimming and magnetophoresis, in which this cooperative effect was a function of separation distance from the magnet. As the microbot approached the magnet, the magnetophoretic force suppressed its self-swimming behavior, leading to a positive magnetotaxis of the microbot toward the source of magnetic field. The use of a high magnetic mass of microbead enhanced the acceleration of the microbot and expanded the acceleration radius, suggesting that the spatial magnetotactic control of microbot in the magnetic field can be achieved by varying its magnetic mass.