Experimental Analysis of Magnetophoretic Separation in Microchannels

ABSTRACT

Magnetophoretic isolation of biochemical and organic entities in a microfluidic environment is a popular tool for a wide range of bio-MEMS applications, including biosensors. In the present work an experimental analysis of magnetophoretic capture of magnetic microspheres in a microfluidic channel under the influence of an external field is investigated. Fluidic transport of the magnetic microspheres has been controlled using suitable guiding magnetic fields. Experiments are performed by varying four parameters namely viscosity, dipole strength, particle size and flow rate. It has been observed that in absence of any magnetic field, particles are carried away with the pressure-driven flow without any capture. The first sign of capture is observed only when the current in the electromagnet is increased beyond a critical capture current (I_cr). The critical current is recorded for different combinations of flow rate Q, the fluid viscosity n, the relative position of the dipole, and particle size. For a particular dipole position the critical capture parameter Π_crit = (I_crita)²/Qη, that is proportional to the ratio of the magnetic force to viscous force, is found to remain invariant.

The magnetophoretic capture efficiency is evaluated as a function of a nondimensional number Π* =χP²a²/(U_maxηh⁵), Results of this investigation can be applied for the selection of the operating parameters and for prediction of device performance of practical microfluidic separators.

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