Mikrosfera magnet, yang terdiri daripada teras polistirena (PS), nanopartikel oksida besi (IONPs) dan polielektrolit kationik, disintesis melalui teknik penyusunan secara berlapis-lapis. IONPs disintesis melalui kaedah pemendakan bersama. Pengendapan IONPs diikuti dengan polielektrolik pada permukaan teras PS dikenal pasti melalui pemeriksaan kegerakan elektroforesis. Morfologi teras-petala mikrosfera magnet dibuktikan melalui mikrograf mikroskopi transmisi elektron manakala jisim magnet dan sifat magnetnya dikaji dengan menggunakan spektroskopi serapan atom dan magnetometer sampel bergetar. Mikro-robot magnetik buatan dibentuk dengan mengikatkan mikrosfera magnet dengan mikroalga melalui saling tindak elektrostatik. Tingkah laku kinematik mikro-robot yang membawa mikrosfera magnet dengan diameter 2 μm dan 4.5 μm telah dikaji di bawah pengaruh dan tanpa pengaruh medan magnet berkecerunan rendah (∇𝐵<100 T/m). Dalam keadaan tanpa pengaruh medan magnet, mikro-robot bergerak secara heliks akibat daripada salah jajaran antara daya tujah dan paksi simetri mikrosfera. Mikro-robot yang diikat dengan mikrosfera magnet yang bersaiz besar bergerak dengan halaju translasi yang tinggi tetapi berputar perlahan pada paksi putarannya. Keseimbangan antara daya kelikatan bendalir dengan daya tujah mikro-robot menyebabkan mikro-robot bergerak secara rawak dengan halaju terminal. Sebaliknya, di bawah pengaruh medan magnet berkecerunan rendah, kawalan terarah mikro-robot tercapai berdasarkan prinsip-prinsip berikut: (1) daya magnetoforesis tidak berperanan untuk mempengaruhi pergerakan seranjang mikro-robot, dan, (2) pergerakan selari mikro-robot bergantung pada kemotilan mikro-robot and magnetoforesis, di mana kesan koperatif ini dipengaruhi oleh jarak pemisahan antara mikro-robot dengan magnet. Apabila mikro-robot mendekati magnet, penahanan daya magnetoforesis terhadap kemotilan mikro-robot diri membawa kepada pergerakan magnetotaksis positif mikro-robot ke arah sumber medan magnet. Penggunaan mikrosfera yang mempunyai jisim magnet yang tinggi boleh meningkatkan pecutan mikro-robot dan memperluas jejari pecutan. Keputusan ini menandakan kawalan magnetotaktik terhadap mikro-robot dalam medan magnet dapat dicapai dengan memanipulasikan jisim magnetnya.
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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.
Kinematic study of motile microalgae under the influence of low gradient magnetic field / Ng Wei Ming