New Chemical Sensing Technique

Wednesday, June 29, 2016 @ 12:06 PM gHale


A new technique to determine the chemical composition of materials using near-infrared light is now in development.

The technique could have a number of potential applications, including improving downhole drilling analysis in the oil and gas industry and broadening the spectrum of solar light that can end up harvested and converted to electricity, said Wei-Chuan Shih, associate professor of electrical and computer engineering at the University of Houston and lead author of a paper describing the discovery.

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“From a scientific point of view, it’s quite a novel discovery to excite plasmonic resonance at near-infrared and make it work for us,” he said.

That means substances sensors operating on the infrared spectrum couldn’t accurately measure can now end up studied in far more detail.

Spectroscopy using the infrared spectrum — an analytical technique using infrared light to scan and identify the chemical composition of organic, polymeric and some inorganic materials — is an important tool, but it has limitations. Infrared light ends up absorbed by water, so the technique doesn’t work with water-based samples.

Near-infrared light scanning is compatible with water, but current techniques are less sensitive than those using other wavelengths.

“To overcome these barriers, we have developed a novel technique to simultaneously obtain chemical and refractive index sensing in 1-2.5 μm NIR (near infrared) wavelength range on nanoporous gold (NPG) disks, which feature high-density plasmonic hot-spots of localized electric field enhancement,” the researchers said. “For the first time, surface-enhanced near-infrared absorption (SENIRA) spectroscopy has been demonstrated for high sensitivity chemical detection.”

Shih said working with near infrared light is usually “a double-edged sword,” as it can end up used with water-based samples but doesn’t provide the needed detail. “We showed water is not an issue, but we can also increase the sensitivity of what we want to measure by 10,000 times,” he said.

He and members of his lab have worked with nanoporous gold disks since discovering the structure in 2013. For this project, he said they “tuned,” or designed, the nanodisks to react when exposed to specific wavelengths, making it possible to develop a sensing technique with the advantages of infrared and near infrared scanning.

The technique ended up tested with various crude oil and other hydrocarbon samples, and Shih said it could be helpful in downhole fluid analysis, which uses near infrared spectroscopy to analyze material found deep in a well. The technique allows drillers to know quickly what’s below the ground or seabed, but he said the new technique could simplify the process because it requires a smaller sample for analysis, an obvious advantage in laboratory characterization.

Oliver C. Mullins, a scientific advisor at Schlumberger and the primary originator of downhole fluid analysis, said the discovery holds potential for both the lab and the field.

“Optical spectroscopy has made significant contributions in the oil and gas industry beyond laboratory characterization,” he said. “In particular, in situ fluid analysis in oil wells based on vibrational overtones and electronic absorption in the visible and near-infrared wavelengths has become an industry standard in wireline well logging. SENIRA brings in an exciting prospect for potential better sensor technology in both field and laboratory settings.”

Shih said researchers are thinking about new ways to do things using the technique. “We can do a lot of oil typing with tiny amounts of oil.”