(237c) Dielectrophoretic Separation of Particles In a Multi-Section Device

Dielectrophoresis (DEP) is the electrokinetic movement of particles due to polarization effects in the presence of non-uniform electric fields. In insulator-based dielectrophoresis (iDEP) regions of low and high electric field intensity, i.e., non-uniformity of electric field, are produced when insulators are present between two electrodes. This technique is increasingly being studied for the manipulation of a wide variety of particles, and novel designs are continuously developed. Despite significant advances in the area, complex mixture separation and sample fractionation continues being one the most important challenges.

In this work, a microchannel design manufactured in PDMS is presented for carrying out DC-iDEP separation of a mixture of particles. The device comprises a main channel with two sections of cylindrical posts with different diameters to create diverse regions of free-space/channel-width ratio. This ratio difference produce diverse regions of electric field gradients designed for the discrimination and separation of particles of several sizes. Each section of the device has a side channel for the collection of the separated and concentrated particles in a different outlet by EOF. The first section encloses posts of 437 mm in diameter arranged 487 mm center-to-center which produce a 0.126 free-space/channel-width ratio, while the posts in the second section have a diameter of 613 mm and are arranged 653 mm center-to-center with a ratio value of 0.08. Electric fields were applied in different locations at different times using a high voltage sequencer: i) across the length of the main channel so particles could be trapped at the two post arrays by negative DEP; and ii) between the side channels to collect the concentrated and separated microspheres by means of EOF.

By applying an electric potential of 800 V between in the main channel, a mixture of 1 (green) and 4 mm (red) polystyrene microspheres were dielectrophoretically separated and concentrated at the same time and then redirected to different outlets. This is achieved due to the different gradient of the electric field created by the two sections in the microdevice. This means that when a specific voltage is applied between the inlet and outlet reservoirs, its gradient will be different for each one of the two post sections. The insulators in the second section, that create a lower free-space/channel-width ratio, will have the greatest gradient of the electric field and therefore the highest value for the DEP force. Thus, a smaller value for the electric field will be needed to overcome EK and achieve particle trapping. In order to get a similar effect on the dielectrophoretic behavior for example on the first section of the device (with a higher ratio) a higher electric field will be needed.

These results demonstrate the flexibility of DC-iDEP as a technique where by combining different designs it is possible to achieve separation and individual collection of particles from a mixture. This work provides guidelines for the development and design of microdevices to be employed for the sorting, concentration and collection of particles by means of DC-iDEP.