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‹‹‹ Contents page for this issue     |     Winter 2010

Technology developed for national security advances cancer detection

By Lynn Nystrom, College of Engineering

Building upon novel technology developed while working on Homeland Security projects at Sandia National Laboratories (SNL) as well as projects from his biomedical graduate student days at the University of California, Berkeley, Rafael V. Davalos is now creating unique microsystems that are showing considerable promise for the detection of cancer and for the study of the progression of this disease.

The story unfolds from the days Davalos was an undergraduate engineering student at Cornell, where he broke his wrist in several places. Today, he can still point to his permanent scars where the doctor customized an external fixation system to his wrist using four screws to keep it in place. Knowing there had to be a better “mousetrap,” he began to focus on biomechanics. As a graduate student at Berkeley, one of his projects was to help develop a microfluidic technology to study life at the smallest system, the living cell.

While Davalos was pursuing his master’s and doctoral degrees in mechanical engineering focusing on bioengineering, he worked with SNL from 1995 until 2006. In the late 1990s at the U.S. Department of Energy laboratory, he delved further into the world of microfluidics, or the behavior of fluids at the microscale level. A relatively new technology, it had already shown promise in revolutionizing certain procedures in molecular biology and proteomics, among other fields.

In the early part of this decade, Davalos helped engineer microsystems for the detection of water-borne pathogens using a technique called dielectrophoresis (DEP), which separates and identifies cells and microparticles suspended in a medium based on their size and electrical properties.

Using the technology, which can detect bacteria in water, Davalos continues to work with his colleague at Sandia, Blake A. Simmons, vice president of the Deconstruction Division of the Joint BioEnergy Institute and manager of the Energy Systems Department at SNL. They hypothesized that the technology could be reconfigured to detect cancer cells by injecting a blood or saliva sample into their microfluidic chip. The samples would be screened based on cancer cells’ electrical signatures.

“Unfortunately, direct translation was not possible due to the need to apply high electric fields in conductive physiological solutions, such as blood, as compared to tap water,” Davalos says. However, the lessons learned and engineering that went into developing robust and reliable microsystems at SNL motivated his team to come up with a viable solution.

Today, Davalos, an award-winning assistant professor of biomedical engineering at Virginia Tech, along with his graduate students, Hadi Shafiee, John Caldwell, and Michael Sano, have found a way to provide “the non-uniform electric field required for DEP that does not require electrodes to contact the sample fluid.”

They call their variation of DEP “contactless dielectrophoresis” (cDEP). Instead of having the electrodes contact the sample fluid, they are capacitively coupled to a fluidic channel in his device through barriers that act as insulators. High-frequency electric fields are then applied to these electrodes, inducing an electric field in the channel. The researchers’ initial studies illustrate the potential of this technique to identify cells through their unique electrical responses without fear of contamination from electrodes or significant joule heating.

The significance of this work is that it “enables a robust method to screen for targeted cells based on the dielectrophoretic properties from an entire blood sample rather than a few microliters,” says Davalos, who is now the director of Virginia Tech’s Bioelectromechanical Systems Laboratory.

“With the microfluidic devices, researchers are able to selectively isolate a cell and let the others float by,” says Davalos. The behavior of specific breast cancer and leukemia cells traveling through the device under static conditions is significantly different than when an electric field was applied, the researchers observed.

“I’m really proud of my students. Our vision would not have been realized without Hadi and Mike’s creativity and John’s ability to engineer some crazy ideas,” says Davalos.

The application of DEP to separate target cells from a solution has been studied extensively in the past two decades, Davalos acknowledges. There are examples of successful separation of human leukemia cells from red blood cells in an isotonic solution and the entrapment of human breast cancer cells from blood. “Although the microelectrode-based devices used in such experiments are useful for studying fundamental biophysics, they are not viable solutions that can be used in a doctor’s office.”

With support from the Jeffress Foundation and the Virginia Tech Institute for Critical Technology and Applied Science, Davalos and his students designed and fabricated a specific microfluidic device to observe the cDEP response of cells using a simple and reliable fabrication process. They determined that the cDEP technique had a heightened sensitivity to isolate cells with close electrical properties, and thus should be successful in separating, for example, normal breast cells from breast cancer cells.

Davalos continues to collaborate with his SNL colleague Simmons to develop DEP technology. The prominence of their work was illustrated by the cover story treatment of their article in the January 16, 2008, issue of the journal Analytical and Bioanalytical Chemistry, written with colleagues Gregory J. McGraw, Thomas I. Wallow, Alfredo M. Morales, Karen L. Krafcik, Yolanda Fintschenko, and Eric B. Cummings.

The result of their cDEP work “highlights the ability of the technique to differentiate cells by their intrinsic electrical properties,” Shafiee, Caldwell, Sano, and Davalos conclude in their paper in the May 5, 2009, issue of Biomedical Microdevice. As a result, they believe their work improves upon existing techniques to separate and identify cells and microparticles suspended in a medium based on their size or electrical properties.

Their new design approach also overcomes the destruction or death of cells due to high temperatures commonly used in the standard use of dielectrophoresis. A provisional patent has been filed on this technique. Davalos was also invited to give a talk on these results at the American Institute of Chemical Engineer’s 2009 annual meeting.

As Davalos and his students in the Virginia Tech–Wake Forest University School of Biomedical Engineering and Sciences steadily progress with their research for treating cancer, he considers how his work today differs from his time with the Sandia Lab. “The Homeland Security work was incredibly important but you hoped it was never used. Now that we are adapting the work to develop something to treat cancer, we actually want to get it used as soon as possible.”

 

The image of a chip containing a multitude of cDEP microdevices. Each device looks like a bug. Four devices surround the Virginia Tech initials. Photo by John McCormick.

Erin Henslee and Rafael Davalos are holding a cDEP chip and discussing which set of channels to use for experiments. Henslee, an SBES master’s student, is now working on cDEP. Photo by John McCormick.

Hadi Shafiee, above left, a Ph.D. candidate in engineering science and mechanics, and Rafael Davalos discuss the experimental results of their work, displayed on the two screens. The left screen shows one device that is primed and ready for use, while the one on the right illustrates human leukemia cells (in the blue color) being selectively trapped using the new technology, contactless dielectrophoresis (cDEP). Photo by John McCormick.

Hadi Shafiee, Erin Henslee, and Mike Sano are discussing the theory behind cDEP to develop new designs. Photo by John McCormick.

Mike Sano is preparing for experiments by placing a cDEP chip on the microscope. Sano is earning his master’s degree in engineering science and mechanics and a Ph.D. in the Virginia Tech-Wake Forest University School of Biomedical Engineering and Sciences (SBES). Photo by John McCormick.

John Caldwell, a master’s student in electrical engineering, is working on the next-generation electronics platform to drive the cDEP technology. Photo by John McCormick.