(372g) Particle Manipulation In a Multi-Section Insulator-Based Dielectrophoresis Microdevice

Particle separation and concentration has become very important as an analytical method; however, performing such operations is not simple due to similarities in physical and chemical properties of the analytes on complex samples. Many techniques have been developed with the aim of purifying samples, but there is still a wide area of opportunity in terms of resolution and efficiency. Driven by advances in electronics, miniaturization offers an alternative with minimal usage of substances and samples, decrease of wastes, shorter process times, greater sensitivity and portability. Nowadays fabrication techniques allow for novel designs to improve separation technologies. One of such technologies is dielectrophoresis (DEP), an electrokinetic transport mechanism of particles due to polarization effects in the presence of non-uniform electric fields [1]. The most common approach to apply DEP is with AC electric fields employing arrays of microelectrodes [2]. However, manufacture of microdevices with electrode arrays can be expensive and device performance is affected by electrode degradation [3]. An alternative to produce nonuniform electric field is to employ insulating structures between two electrodes, i.e., insulator-based dielectrophoresis (iDEP). Despite of being a nascent technique, there have been many successful microdevice designs used to separate mixtures of particles according to their dielectrophoretic response. Kang, et al. [4], developed a microchannel with an insulating hurdle that allowed separation of particles by deflecting their electrokinetic path according to their size. The particles experience negative DEP at the corners of the block which magnitude depends on their volume. With their design the authors could continuously separate a mixture of two different polystyrene microspheres. Using the same principle but with a circular channel with electrodes on its extremes, Zhang, et al. [5], suggested continuous sorting of particles by their size. Pysher and Hayes [6] developed a saw-tooth microchannel which tooth dimensions change along the channel. In this design the width of the channel gradually decreased in the direction of the flow, leading to a gradual increase of the electric field gradient, and therefore the increasing the DEP force. They reported the separation of live and dead samples of Bacillus subtilis, Escherichia coli and Staphylococcus epidermis in different regions of the same microdevice. In the present study, insulating cylindrical posts are used to produce a nonuniform electric field and dielectrophoretically trap polystyrene microspheres of different sizes, employing DC electric fields. The microdevice employed was manufactured from glass arrays of cylindrical post of different diameters, which creates regions with different magnitudes of dielectrophoretic forces. In this way, with a specific electric field, a mixture of particles can be sorted by size and trapped in the region where negative dielectrophoretic force overcomes electroosmotic flow. Each section of the microdevice has its own outlet, allowing for the concentrated and separated sample to be recovered. Results show that the spheres exhibited negative DEP under direct current electric fields, where the larger particles showed stronger response. A complex mixture of particles could then be fractionated and simultaneously concentrated, demonstrating the great potential of the technique to handle complex samples.

References

1. Phol, H. A., 1951. The motion and precipitation of suspensoids in divergent electric fields. Journal of Applied Physics. Vol. 22: 869.

2. Washizu, M., Kurosawa, O., 1990. Electrostatic manipulation of DNA in microfabricated structures. IEEE Transactions on Industry applications Appl. 26, 1165-1172.

3. Lapizco-Encinas, B.H., Simmons, B.A., Cummings, E.B., Fintschenko, Y., 2004. Dielectrophoretic Concentration and Separation of Live and Dead Bacteria in an Array of Insulators. Analytical Chemistry. 76, 1571-1579.

4.Kang, K.H., Kang, Y.J,. Xuan, X.C., Li, D.Q., 2006. Continuous separation of microparticles by size with Direct current-dielectrophoresis. Electrophoresis. 27, 694-702.

5. Zhang, L., Tatar, F., Turmezei, P., Bastemeijer, J., Mollinger, J.R., Piciu, O., Bossche, A., 2006. Continuous Electrodeless Dielectrophoretic Separation in a Circular Channel. Journal of Physics: Conferences Series. 34, 527-532.

6. Pysher, M.D., Hayes, M.A., 2007. Electrophoretic and Dielectrophoretic Field Gradient Technique for Separating Bioparticles. Analytical Chemistry. 79, 4552-4557.