Say hello to SENIRA: Oil's well

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  • Published: Jul 1, 2016
  • Author: David Bradley
  • Channels: Infrared Spectroscopy
thumbnail image: Say hello to SENIRA: Oil's well

SENIRA

University of Houston researchers report that for the first time, surface-enhanced near-infrared absorption (SENIRA) spectroscopy has been demonstrated for high sensitivity chemical detection. (Credit American Chemical Society/University of Houston)

Researchers in the US have demonstrated for the first time that surface-enhanced near-infrared absorption (SENIRA) spectroscopy can be used as a highly sensitive analytical tool. While NIR absorption spectroscopy is rather useful for extracting molecular and chemical information through the overtones and combination bands of a molecule's fundamental vibrational modes, its sensitivity is limited somewhat by weak absorption and less effective detector performance when compared with spectroscopic techniques in other wavelength ranges.

Now, Wei-Chuan Shih, Greggy Santos, Fusheng Zhao, Oussama Zenasni, and Md Masud Parvez Arnob of the University of Houston, in Texas, believe they have found a way to improve this technique considerably that would open up new applications in downhole drilling analysis in the oil and gas industry and perhaps even broadening the spectrum of solar light that can be harvested and converted to electricity. The new technique is also more compatible with samples containing water. Shih and colleagues report details in the journal Nano Letters.

"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," Shih says.

We shall overcome

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

Shih adds that working with NIR is usually "a double-edged sword," as it can be used with water-based samples but does not provide adequate detail in my experiments. "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 says.

Direct to disk

The researchers have been investigating nanoporous gold disks since discovering the structure in 2013. In the present study they have designed, or tuned, the nanodisks to react in a particular way when exposed to specific wavelengths, making it possible to develop a sensing technique with the advantages of both IR and NIR scanning. Proof of principle was demonstrated with various crude oil samples as well as hydrocarbon samples, which given their location is of particular commercial interest. The technique would be useful in downhole fluid analysis, which uses near infrared spectroscopy to analyse material found deep in an oil or gas well. Usually, the technique allows those drilling for oil to quickly discovery what is below the ground or seabed. However, the new technique will simplify this discovery process partly because it requires a smaller sample that can be handled more easily for laboratory characterization.

Optical spectroscopy has been widely used by the industry for in situ fluid analysis, indeed at these wavelengths it is the industry standard for "wireline" well logging. However, SENIRA offers a new prospect in the field and in the laboratory. Shih explains that the researchers are thinking about how the technique might best be implemented in each setting. "We can do a lot of oil typing with tiny amounts of oil," he says. The first overtones of the C-H vibration in the 1600 to 1800 nanometre region are very different for different liquid hydrocarbons, so the SENIRA approach will be particularly useful for distinguishing crude oils, particularly those rich in asphaltenes. However, while the Texas team's work focused on oil and hydrocarbon samples, the same approach could be used for samples containing any molecules of interest.

Shih told SpectroscopyNOW that is looking to new collaborators and funding. "There are many things we’d like to study regarding this mechanism from harvesting the solar spectrum to bioimaging and sensing," he added.

Related Links

Nano Lett 2016, online: "Simultaneous Chemical and Refractive Index Sensing in the 1–2.5 µm Near-Infrared Wavelength Range on Nanoporous Gold Disks"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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