SUMMARY

Many scientists and engineers are turning to lab-on-a-chip systems for faster and cheaper analysis of chemical reactions and biomolecular interactions. A common approach that facilitates the handling of reagents and biomolecules in these systems utilizes micro/nano beads as the solid carrier. Physical manipulation, such as assembly, transport, sorting, and tweezing, of beads on chip represents an essential step for fully utilizing their potentials in a wide spectrum of bead-based analysis. Previous work on bead manipulation was demonstrated with either an ensemble of beads, or on single beads but lacks the capability for parallel operation. Parallel manipulation of individual beads is required to meet the demand for high-throughput and location-specific analysis. In this work, we developed two new methods for parallel manipulation of individual polymer microbeads doped with magnetic nanobeads. The first method employs arrays of microscale soft magnets fabricated inside a microfluidic channel and subjected to an external magnetic field. We demonstrated that the system can be used to assemble individual beads (1µm) from a flow of suspended beads into a regular array on the chip, hence improving the integrated electrochemical detection of biomolecules bound to the bead surface. By rotating the external field, we demonstrated that the assembled microbeads can be remotely controlled with synchronized, high-speed orbital motion around the soft magnets. We employed this manipulation mode for efficient microfluidic mixing in continuous flow. Furthermore, we discovered a simple but effective way of transporting the microbeads across an array of soft magnets by varying the magnetic field strength within a revolution of the external field. The transport mechanism was utilized for on-chip sample separation purposes. Our second method in parallel manipulation of individual microbeads integrates magnetic and dielectrophoretic manipulations. The device combines tapered conducting wires and fingered electrodes to generate desirable magnetic and electric fields, respectively. By externally fine-tuning the magnetic attraction and dielectrophoretic repulsion forces, out-of-plane motion of the microbeads at high spatial resolutions were realized. This manipulation mode has many promising applications in lab-on-a-chip systems and biomolecular engineering, among which the development of massively parallel biomolecular tweezers is under way.