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In recent years, magnetophoresis has gained significant advances in precise manipulation of particles/cells for numerous applications including gene sequencing, diagnostic, single cell analysis and separation, which can be achieved using nano/micro scale magnets in microfluidic environment with the help of applied magnetic field. Generally, magetophoresis can be classified as either positive magnetophoresis or negative magnetophoresis depending on the magnetizable property of particles/cells and the surrounding medium. Here, in positive magnetophoresis, the individual magnetic particles are manipulated on the micro-magnetic patterns and in the negative magnetophoresis, the individual non-magnetic particles/cells are manipulated on the magnetic micro-cavity pattern by applying an external magnetic field. The design and fabrication of magnetic and magnetic micro-cavity patterns for logical manipulation of particles/cells are presented.
When the magnetic particles are manipulated under an applied in-plane rotating magnetic fields on the micromagnetic pattern, the behavior of particles on streptavidin/Teflon interface between the colloids and the micromagnet arrays were obtained using the magnetic forces at the phase-locked angles.
Further, the fabrication of on-chip micro-magnets using Ni80Fe20 and Co70Fe30 materials were presented to understand the mobility of superparamagnetic (SPM) particles. The maximum velocity of the particles around the periphery of the micromagnets is determined by the critical frequency, which indicates that the particle enters the phase-slipping regime from the phase-locked regime. The maximum velocity of NiFe micromagnets is approximately 3 times larger than that of CoFe micromagnets measured at the low field regions. Moreover, the maximum velocity of the particles is decreasing with increasing the thickness of Teflon coating on the micromagnets, which is in a good agreement with the variation of the magnetostatic potential energy evaluated numerically from micromagnetic simulations.
Micromagnetic simulations were performed using Mumax3 and Matlab software to calculate the magnetic domains of the patterned micromagnets, local magnetic hysteresis loops on the patterned magnetic surface, magnetic force and potential energies of the particles to understand their transport mechanism on the micromagnetic pathways.
When the non-magnetic particles are manipulated under applied strong magnetic fields on the magnetic micro-cavity pattern, a novel Pseudo diamagnetophoresis concept is introduced in place of negative magnetophoresis. The motion of label free cells are shown by introducing ferrofluids in this concept. Specifically, we develop herein a new approach to obtain independent control and directional manipulation of PsD particles, and label-free cells without needs to know the biomarkers. The logic manipulation is based on geometrical parameters of the magnetic micro-cavity patterns, the size difference of particles/cells, which is conducted in a custom-made biocompatible ferrofluid that retains the viability of cells during experiments. The magnetic micro-cavity tracks can actively switch the particles/cells at the junction which resembles an electrical diode, navigating to different directions and desired locations. The switching efficiency of particles/cells is characterized with various eclipse ratios and at various gaps between the horizontal and vertical patterns of the magnetic micro-cavity junctions. The suitable particle/cell sizes and the geometrical parameters of the magnetic micro-cavity junctions are studied to achieve successful logic manipulation of single particles/cells. This unique approach opens a door for development of label-free cells manipulation with high throughput, efficiency and reliability.
