June 21, 2006|
Microchannels, electricity aid drug discovery, early diagnosisWEST LAFAYETTE, Ind. A tiny fluid-filled channel on a microchip that allows single cells to be treated and analyzed could lead to advances in drug and gene screening and early disease diagnosis.
"Normally when you do testing, you need a lot of cells, and the properties that you record are the average of that cell population," Lu said. "If you carry out the test based on single cells, you have access to a more detailed picture of the cell population and can pinpoint abnormalities more quickly and exactly."
The size of the channel, while small enough to accommodate only one cell at its narrowest diameter, varies in width so that the electric field intensity differs depending on the cell's location in the device, Lu said. The flow rate controls how much time the cell spends in the high electrical field, where a process called electroporation occurs. Controlling the length of time in the high electrical field without turning the voltage on and off helps maintain the cell's viability.
Electroporation, which use electricity to treat cells, opens pores in the cell's outer membrane. This allows materials outside the cell that ordinarily couldn't penetrate the membrane to move through it.
Lu's research team's findings on the development and use of the new device are published online by the journal Analytical Chemistry, a publication of the American Chemical Society. The article is scheduled for the July 1 issue of the print publication.
The Purdue Research Foundation has filed a provisional patent on Lu's technology, and the Purdue Office of Technology Commercialization is working on licensing the device.
The device, called a microfluidic channel, has a liquid buffer moving cells through the channel.
"This device is extremely simple and can be made very cheaply," Lu said. "You only need a single microfluidic channel to achieve this electroporation process, and potentially we can run multiple devices in parallel on a chip. This is very important for efficient, successful screening of drugs and genes."
In this study, the researchers also demonstrated that they could permanently disrupt the membrane so that a cell would release intracellular materials, making it possible for scientists to analyze the inner materials of a single cell.
"This is important for rare cell detection," Lu said. "If you have a very low number of a certain type of cell that is a precursor for a disease, such as some form of cancer, those cells may be buried in the average cell population data of a bulk cell test."
The Purdue Center for Food Safety Engineering currently is funding further research on the device for use in bacteria detection to protect against natural or purposeful introduction of contaminants into the food supply.
The researchers used Chinese hamster ovary cells inserted into the channel equipped with electrodes. A syringe pump continuously transported the liquid and the cells into the channel where they passed through the electrical field.
The electroporation microfluidic device has the potential to screen for many diseases and for determining the basic functions of genes, Lu said.
"Because the device is so small, eventually we'll be able to screen hundreds of genes or drugs at a time with a number of the channels integrated on the same chip," he said.
The Purdue College of Agriculture and Bindley Biosciences Center provided funding for this work.
The other author of the study was Hsiang-Yu Wang, a Purdue School of Chemical Engineering graduate student. Lu, an assistant professor in Purdue's Department of Agricultural and Biological Engineering and School of Chemical Engineering, is affiliated with the Laboratory of Renewable Resources Engineering and several centers at Purdue's Discovery Park, including the Bindley Bioscience Center, Birck Nanotechnology Center, Center for the Environment and Oncological Sciences Center.
Purdue researcher Chang Lu, from left, and Hsiang-Yu Wang demonstrate a low-powered laser used to view a microchip through a microscope. Wang, a graduate student in chemical engineering, is a member of Lu's research team. Lu's research could lead to advances in drug and gene screening and early disease diagnosis. (Purdue Agricultural Communication photo/Tom Campbell)
A publication-quality photo is available at http://news.uns.purdue.edu/uns/images/+2006/lu-cellchannel.jpg
Electroporation of mammalian cells in a microfluidic channel with geometric variation
Hsiang-Yu Wang, Chang Lu* School of Chemical Engineering, Department of Sc, Purdue University, IN 47907 (*Corresponding author: Chang Lu, Department of Agricultural and Biological Engineering and School of Chemical Engineering, 225 S. University Street, West Lafayette, IN 47907)
Electroporation has been widely used to load impermeant exogenous molecules into cells. Rapid electrical lysis based on electroporation has also been applied to analyze intracellular materials at single cell level. There has been increasing demand to implement electroporation in a microfluidic format as a basic tool for applications ranging from screening of drugs and genes to studies of intracellular dynamics. In this report, we have developed a simple technique to electroporate mammalian cells with high throughput on a microfluidic platform. In our design, electroporation only happened in a defined section of a microfluidic channel due to the local field amplification by geometric variation. The time of exposure of the cells to this high field was determined by the velocity of the cells and the length of the section. The change in the cell morphology during electroporation was observed in real time. We determined that electroporation of Chinese hamster ovary (CHO) cells occurred when the local field strength was increased to around 400 V/cm. The internalization of membrane-impermeant molecules (SYTOX green) with cell viability preserved was also carried out to demonstrate transient electropermeabilization. The influence of the operational parameters of the device on cell viability was determined. A large percentage of cells remained viable after electroporation when the parameters were tuned. We also studied rapid cell lysis when the field intensity was in the range of 600-1200 V/cm. The rupture of cell membrane happened within 30 ms when the field strength was 1200 V/cm. Given the simplicity, high throughput, and high compatibility with other devices, this microfluidic electroporation technique may increase the application of microfluidic systems in screening of drugs and biomolecules and chemical cytometry.
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