DARPA awards $1.2M grant to study surface enhanced Raman scattering

CAMBRIDGE, Mass. - July 17, 2008 - The Defense Advanced Research Projects Agency (DARPA) has awarded a $1.2 million grant to an interdisciplinary team of Harvard University researchers to study surface enhanced Raman scattering (SERS) for the first phase of a potential three-year effort. If all phases of the development program are completed, researchers could receive up a total of up to $2.9 million in funding.

Ken Crozier, Assistant Professor of Electrical Engineering at the School of Engineering and Applied Sciences (SEAS) will serve as the principal investigator for the grant. His co-investigators include Eric Mazur, Balkanski Professor of Physics and Applied Physics at SEAS and the Department of Physics and Alán Aspuru-Guzik, Assistant Professor of Chemistry and Chemical Biology at the Department of Chemistry and Chemical Biology.

SERS relies upon a fundamental phenomenon in physics called the Raman effect—the change in the frequency of monochromatic light (such as a laser) when it passes through a substance. Properly harnessed, Raman scattering can identify specific molecules by detecting their characteristic spectral fingerprints. Potential applications of SERS include the sensing and identification of a range of materials, including chemical and biological agents, improvised explosive devices, and toxic industrial waste.

“While SERS offers enormous potential for chemical detection and sensing, its practical use has been hampered by the need for improved knowledge of the fundamentals of the enhancement mechanisms,” says Crozier.

It turns out that Raman scattering cross sections are very small, about 10^12-10^14 times smaller than fluorescence cross sections. In the 1970’s scientists discovered that by placing molecules on roughened metal surfaces they could achieve significantly larger Raman signals, enabling the detection of molecules. Nevertheless the gain has not been enough to make SERS readily usable in detection devices.

“By applying recent advances in optical antennas, laser nanostructuring, and theoretical chemistry, we aim to elucidate the fundamental mechanisms underlying SERS and demonstrate high-performance SERS substrates that will enable the technology to go to the next stage of development,” says Crozier.

In particular, the team will utilize Crozier’s recent work on optical antennas, metallic nanostructures that are able to generate intense electric fields, by modelling, fabricating and characterizing SERS optical antenna chips. SERS measurements on these chips will allow precise determination of the effects of optical antenna parameters, such as size, shape and spacing requirements, on SERS enhancement.

Likewise, to fabricate large area SERS substrates, the researchers will employ Mazur’s expertise in femtosecond laser-nanostructured (FSLN) semiconductor surfaces, or what is more commonly known as “black silicon.” Because not all metallic nanoparticles are equally SERS-active, they will also create a screening process to separate the two.

Finally, by relying on Aspuru-Guzik’s expertise in theoretical modeling the team will investigate the interplay between chemical and electromagnetic enhancement and, based upon their findings, develop an integrated electronic structure package in a complex electromagnetic environment.

To help foster the research, Crozier plans to collaborate with two existing Harvard-based centers, the Nanoscale Science and Engineering Center and the Center for Nanoscale Systems, a member of the National Nanotechnology Infrastructure Network.