Originally Published MDDI January 2006
R&D Digest: The monthly review of new technologies and medical device innovations.
By Maria Fontanazza
A device that can identify bacteria in water within minutes could have use both in early disease detection and on the operating table. Researchers at Sandia National Laboratories (Livermore, CA) developed an insulator-based dielectrophoretic (iDEP) device that quickly analyzes samples without overnight culturing. The lab is looking for commercial partners to further develop the iDEP technology.
“It could get you an answer in the field right away,” says Eric Cummings, principal member of the technical staff at Sandia. “For a lot of applications, that's what you need.”
The device has been proven to distinguish live cells from dead ones and to detect specific cell types. Now the researchers need to focus on application-specific engineering. “For example, an aerosol collector would have a different format and buffer system than a blood sample,” says Cummings. The size of the iDEP device could also be adapted to the size of the particles involved.
Cummings foresees the technology helping surgeons during operations to determine whether tissue is cancerous. “You have to ask when it actually matters that you have a real-time answer. This would be an approach.” However, he says this particular application is pretty far down the road. Other possible diagnostic applications include detecting diseases in which abnormal cell structures are present, such as cancer and sickle-cell anemia.
The technology could also replace patch clamping, a technique that records cellular current. “Some of the same things you do with a patch clamp you might be able to do with dielectrophoresis in a very-high-throughput and low-expense fashion,” says Cummings. “That would be interesting future work.” Patch clamping can be costly and labor intensive.
Dielectrophoresis moves particles toward an electrical field. “The reason a particle moves there is that a system is at the minimum potential energy when the most current is flowing,” says Cummings. “By moving the conductive particles to regions where the electric field is high, you move the insulating particles away from those regions. In that way, you approach a more stable potential energy position.” Because the system has a lower energy in this assembly, a force pushes particles toward that arrangement. That force is the dielectrophoretic force; the motion is dielectrophoresis.
The process directly sorts particles based on physical properties. Its advantage over fluorescence-activated cell sorting or conventional cytometry is that it can sort a vast population of cells very quickly.
Standard dielectrophoretic sorters place electrodes in the sampling device, using nearby nonuniform electric fields to trigger cell motion. However, the electrodes make bubbles and an electrolytic result that can damage the device and the cells. “The electrode-based systems are limited in the type or volume of samples they can handle and process,” says Blake Simmons, senior member of Sandia's technical staff.
With iDEP, electrodes are outside the device, and an electrode current goes through particle-bearing liquid into the device. An insulating structure creates the nonuniform electric field. “This is more amenable to scale-up, because insulating structures can span or traverse the entire cross section of a channel. You can process a lot more samples,” says Simmons. There's also no electrolytic result, and the process is gentle on cells.
“There are a lot of techniques already in place in the medical field that could be easily adapted to an input system of a dielectrophoresis device,” says Simmons. However, he notes that this is still a very advanced research tool. “Developing functional devices that can withstand real-world samples is an area we need to work on.”
Sandia's Laboratory-Directed Research and Development Program provided funding for the iDEP device.
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