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For years, officials have used infrared spectroscopy to detect trace amounts of performance-enhancing drugs in a blood sample or tiny bits of explosive bomb materials traveling through the air.
According to a new study in the journal Advanced Optical Materials, Researchers from the University at Buffalo in New York have developed a cutting-edge light sensor that could drastically improve this forensic application of infrared spectroscopy.
The sensor operates inside the mid-infrared part of the electromagnetic spectrum, a region commonly used for most remote controls and night-vision.
The new sensor is made up of two layers of metal with an insulator in the middle. Using a production method known as atomic layer deposition, Scientists produced a device with spaces less than 5 nanometers wide between two metal tiers. Notably, these gaps allow the sensor to absorb as much as 81 percent of infrared light, a considerable advancement from the 3 percent that comparable devices absorb.
The system being examined in the new study is referred to as surface-enhanced infrared absorption (SEIRA) spectroscopy. According to the new study, the sensor developed by the team functioned as a substrate for the materials being tested and it enhanced the sensitivity of SEIRA devices to find molecules at 100 to 1,000 times higher resolution than earlier reported outcomes.
The boost makes SEIRA spectroscopy similar to a different kind of spectroscopic investigation, surface-enhanced Rama spectroscopy (SERS), which gages light scattering compared to light absorption. While SERS is responsive to single molecules, it is confined to molecules that spread light from a broad cross-sectional area. SEIRA, however, may be used to scan just about any molecule that is chemically compatible with the device’s antenna.
The SEIRA advancement might be beneficial in any situation that requires locating traces of molecules, the study team said. This may include, but is not limited to: drug detection in blood samples, sensing of bomb-making materials in the air, identification of fake art and monitoring disease.
The study team said they plan to continue the study, and look at how to combine their SEIRA development with state-of-the-art SERS technology. A successful combination would allow for the creation of a detailed data set of the vibrational signatures when molecules are excited with infrared light.
In 2015, a team of SEIRA Researchers announced the development of a new fan-shaped nanoantenna, which is used to focus light at desired optimal wavelengths. The antenna was made from two gold nanorods with a 10-20 nanometer space between them and relatively large semi-circular “fans” on both sides. The Researchers behind the new antenna said they were able to focus infrared light into a very restricted volume, which is optimal for detection.
The study team said their fan-shaped design is more effective than two nanorods alone because each fan section acts as a reservoir of charge carriers that can move towards the gap. With a greater amount of charge carriers, the antenna is able to generate a more robust electrical field in the gap interface. Combined with a gold mirror film placed beneath the antennae that reflected both inbound light and the light scattered from the antenna by itself, the Researchers were able to enhance the field strength by six-fold. This translated to the team being able to recognize much fewer sample molecules than normal by using typical infrared spectroscopy means.
The key factor to the team’s development was the creation of ‘inverted’ features, known as Fano resonances, which are brought on by only a small quantity of molecules.
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