Biochemical Sensing Systems the Size of a Fingernail Tip?

PITTSBURGH—Soldiers in the wars against bioterrorism, disease, and environmental pollution are often weighed down by the bulky equipment required to detect and monitor biochemicals. Current biochemical sensors can be as big as a truck. Even the smallest are the size of laptop computers.

But what if entire biochemical sensing systems could be shrunk to the size of a fingernail tip? Plasmonic chip technology—which may someday enable scientists to squeeze millions of sensor elements onto a single computer chip—promises to create just such "nanoscaled" biochemical sensing systems, says University of Pittsburgh Professor Hong Koo Kim.

The National Science Foundation (NSF) recently awarded Kim a $1.3 million, four-year NSF Nanoscale Interdisciplinary Research Team (NIRT) grant to develop plasmonic chip technologies for biochemical sensing. At a more basic level, Kim and his Pitt colleagues also will investigate the fundamentals of plasmonic phenomena in nanoscale metallic structures.

"If this nanoscaled biochemical sensing technology becomes a reality, it would revolutionize healthcare—including diagnosis of disease and monitoring of health status—as well as our ability to detect toxic and hazardous biochemical agents for environmental and homeland security purposes," said Kim, a professor of electrical and computer engineering and codirector of Pitt's Institute of NanoScience and Engineering.

Kim and his institute colleagues are experts in thinking small, i.e., on a nanoscale

(a nanometer equals one-billionth of a meter). Nanoscientists use atoms and molecules as basic building blocks to construct minute machines, create new materials, or perform molecular tasks.

Surface plasmon is a collective oscillation of electrons that occurs in metals in response to light, Kim explained. "The collective behavior of electrons in metals can result in many interesting phenomena," he noted. "Beautiful colors generated by stained glass represent a good example of this surface plasmon phenomenon: Metallic nanoparticles in stained glass absorb light at different spectral bands and thus reveal characteristic colors."

The characteristic behavior of surface plasmons is governed by both the structure and the materials involved. In Kim's project, specially designed arrays of nanosized holes and slits are being explored as a medium for interaction with light, in place of random structures (such as metallic nanoparticle clusters in stained glass). Thanks to these specially designed arrays, the collective behavior of electrons can be confined within a nanometer-scale aperture, which is far smaller than the wavelength of light.

Kim's NIRT project involves cross-school collaboration with Pitt Professor Hrvoje Petek of the Department of Physics and Astronomy and Professors Rob Coalson, David Waldeck, and Gilbert Walker of Pitt's Department of Chemistry.

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