Handheld microfluidic platforms using magnetic sample pretreatment and detection

Abstract

In microfluidics, magnetophoresis refer to the movement of beads in a solution by an external magnetic field. The beads are attracted in the direction of high magnetic flux density or are pushed in the direction of low magnetic flux density due to the difference in magnetic susceptibility between the beads and the solution surrounding the beads. This magnetophoresis based microfluidic technology is easy to be integrated with other technology thus it is widely utilized for sample pretreatment and detection. However, as with other microfluidic technology, there are limits to the need for several electronic equipment for their operation. In this thesis, we developed a handheld microfluidic platform capable of rapid sample pretreatment and detection without any electrical equipment. With this goal, three magnetophoresis-based microfluidic technology have been developed. First, we developed magnetophoresis technology under static-fluid environment that does not require electrical pumps. To align the beads in the microchannel to initial position with the same magnetic flux density, micro-sized pillar array was designed in the microchannel and a manually operable syringe was connected to the microchannels. In order to overcome the error of the results by the residual flow after stopping the operation of the syringe, the difference of velocity between beads under the same environment was utilized. Second, we developed a vertical magnetophoresis that does not require the initial alignment process of the injected beads. The beads in the capillary tubes, which are erected to the magnet, are gathered at specific height that balances the three different forces (gravity force, magnetic repulsive force, and buoyance force). The beads labeled with magnetic nanoparticles are formed at low height in the capillary tube. In other technology, finger-powered microfluidic devices capable of sample pretreatment based on immunomagnetic separation and colorimetric detection based on magnetic nanoparticle were designed. As a result, this platform was able to detect $10^2$ CFU/mL of Escherichia coli O157:H7.