We are seeking to achieve electronic control of biological and chemical processes in "lab-on-a-chip" type applications.  The method we are currently studying is dielectrophoresis. This physical effect allows voltages on microfabricated electrodes (which we fabricate in the Integrated Nanosystems Research Facility) to manipulate living cells in a solution through electric fields, without ever coming into contact with the cells themselves. This effect may be useful for on-chip preparation of biological and chemical specimens before further chemical, electric, and optical analysis occurs, presumably on the same chip. Although many years away, the integration of all these functions onto a single chip will ultimately allow cost effective mass production of a new generation of diagnostic and analytical tools.

In figure 1, the principle is illustrated schematically. If a polarizable object is placed in an electric field, there will be an induced positive charge on one side of the object and induced negative charge (of the same magnitude as the induced positive charge) on the other side of the object. The positive charge will experience a “pulling” force; the negative charge will experience a “pushing” force. In a uniform field, as depicted in figure 1 a, the “pulling” force will cancel the “pushing” force, and the net force will be zero. However, in a non-uniform field, as depicted in figure 1 b, the electric field will be stronger on one side of the object and weaker on the other side of the object. Hence, the “pulling” and “pushing” forces will not cancel, and there will be a net force on the object.

Figure 1: Schematic depiction of di-electrophoresis. The direction of the arrows represents the direction of the electric field; the length of the arrows represents the magnitude of the electric field. In reality, the electric field lines would bend around the sphere somewhat. We neglect that effect for this simple depiction.

 Figure 2: First generation of UCI dielectrophoresis experiments.

Figure 3: Second generation of UCI dielectrophoresis experiments. There are four electrodes which surround the trap. The central region is approximately 100 mm across.

(If the videos below don't appear, right click on these links to save the files to your computer and then open them manually. You will need the Quicktime program, available at www.quicktime.com.)

beads.MOV

cells.MOV

Video of trapping of beads:

Video of trapping of cells:

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Last modified: 08/20/05