Magnetic Micromanipulation of a Single Magnetic Microsphere in a Microchannel

Abstract

Magnetic microspheres are well known for their ability to provide high surface-to-volume ratio mobile reaction surfaces for chemical and biochemical reactions. Their use in microfluidic devices opens up novel avenues for uses in ‘lab-on-a-chip’ applications, e.g., as magnetic tweezers. Cantilevers and optical tweezers are widely used for micromanipulating cells or biomolecules in order to measure their mechanical properties, or for biosensor applications. However, they do not allow for ease of rotary motion and can sometimes damage the handled material. We present herein a system of magnetic tweezers that uses functionalized magnetic microspheres as mobile substrates for biological and biochemical reactions and offers better manipulation of the cells or organic molecules. The predominant transport issue for these magnetic tweezers is the precise magnetic manipulations of the microbeads so that the chemical/biological reactions at the bead surface are controlled. The best way to obtain unambiguous information about the behavior of particles is to begin with the study of a single isolated particle in a microchannel flow. We have conducted a fundamental study to manipulate an isolated magnetic microparticle using the concept of ‘action-at-a-distance’. An external magnetic field is used to direct and steer the particle across a microchannel. Such a study is directly pertinent to practical applications where usually a small number of such microspheres are utilized, such as DNA sequencing and separation, cell manipulation and separation, exploration of complex biomolecules by specific binding enabling folding and stretching, etc. Numerical simulation of the microchannel flow and particle manipulation is performed using a finite-volume transient CFD code and Lagrangian tracking of magnetic microspheres in the flow under an imposed magnetic field gradient. Experimental validation of the numerical results is then performed. The effects of varying viscosity and flowrate using two different particle sizes are investigated. Parametric study is performed to tune the external magnetic field so as to obtain a desired particle trajectory. Finally, the proof of concept demonstration of the magnetic tweezing is reported. We conclude that magnetic tweezers are viable and can be fabricated as part of a biocompatible setup that could become a suitable alternative to the other available micromanipulators.