Spatial manipulation of cells and organelles using single electrode dielectrophoresis

www.BioTechniques. com 39 Vol. 52 | No. 1 | 2012 Dielectrophoresis (DEP) is a proven technique for characterizing and manipulating cells by imposing forces through applied AC electrical field gradients. This technique, which can be used on diverse cell types and multicellular organisms, has been largely worked on in physics and engineering laboratories and has received limited attention as a potentially useful tool for biologists (1–3). Most studies utilizing DEP use sophisticated planar DEP microelectrode arrays coupled to microf luidics systems for large-scale separation of thousands of cells (4–6). These devices have shown significant advances with the advent of photolithography-based microfabrication technologies and new polymers, however they are not suitable for smallscale separations of rare cells within a heterogeneous population and are not commercially available. Similarly, cell sorting f low cytometers are optimized for high-throughput applications but are not appropriate for all cell types and often require large quantities of sample material that not all applications have the fortune of. Additionally, these systems are costly and often require a trained technician for proper operation. Other cell manipulation technologies, including optical tweezers, enable single cell manipulation but also require highly specialized and expensive instrumentation. We have previously reported a DEP electrode designed to pick out and relocate single target cells from a cell culture (7). The electrode took the form of two electrochemically etched gold wires insulated from each other except for a short region near the electrode tips, which formed the working ends of the DEP “tweezer” design single electrode. Consistent fabrication of this design was difficult, and great care was required in preventing both cell damage arising from contact of cells with electrode tips, as well as damage to the tips themselves. To date, single DEP electrodes have been handmade, making them inherently prone to manufacturing inconsistencies. Fabrication of these designs are technically difficult and require instrumentation not standard to most labs, such as capillary pullers, metal etching equipment, and sputter coaters (7–10). Despite these difficulties, single electrode DEP designs offer advantages over planar designs in single cell manipulation and in small-scale separations of primarily rare cell types. However, both configurations utilizing DEP as a technique have found limited practical use in biological research, in part to technical limitations. Here, we report the characterization and implementation of an improved DEP electrode. Our design is comprised of a single, commercially available microelectrode and requires only a micromanipulator, microscope, and AC signal generator for use. Unlike prior single and planar DEP electrodes, our design is of simpler composition and commercially available, enabling greater consistency and ease of use. Furthermore, our single electrode design provides the ability to select rare cells from a heterogeneous population and applies exacting positive or negative DEP forces to finite regions of a cell. Our design is capacitively coupled to ground, negating the need for a direct ground in the liquid medium and thus aiding in overall experimental setup. In this report, we demonstrate how this electrode is capable of small-scale separations of single cells and demonstrate its ability to assess viability states without the use of chromogens. Lastly, we demonstrate a novel application of single electrode DEP in the spatial manipulation of intracellular organelles.