Dielectrophoretic Traps for Cell Manipulation

One of the goals of biology for the next fifty years is to understand how cells work. This fundamentally requires a diverse set of approaches for performing measurements on cells in order to extract information from them. Manipulating the physical location and organization of cells or other biologically important particles is an important part in this endeavor. Apart from the fact that cell function is tied to their three-dimensional organization, one would like ways to grab onto and position cells. This lets us build up controlled multicellular aggregates, investigate the mechanical properties of cells, the binding properties of their surface proteins, and additionally provides a way to move cells around. In short, it provides physical access to cells that our fingers cannot grasp. Many techniques exist to physically manipulate cells, including optical tweezers [78], acoustic forces [94], surface modification [52], etc. Electrical forces, and in particular dielec-trophoresis (DEP), are an increasingly common modality for enacting these manipulations. Although DEP has been used successfully for many years to separate different cell types (see reviews in [20, 38]), in this chapter I focus on the use of DEP as " electrical tweezers " for manipulating individual cells. In this implementation DEP forces are used to trap or spatially confine cells, and thus the chapter will focus on creating such traps using these forces. While it is quite easy to generate forces on cells with DEP, it is another thing altogether to obtain predetermined quantitative performance. The goal for this chapter is to help others develop an approach to designing these types of systems. The focus will be on trapping cells—which at times are generalized to " particles " —and specifically mammalian