New Nano Sensing Technology

Tuesday, June 2, 2015 @ 06:06 PM gHale

From sensing chemicals, airport security detecting explosives to art historians authenticating paintings, the industry’s need for powerful sensors continues to grow.

Given that, few sensing techniques can match surface-enhanced Raman spectroscopy (SERS). SERS is a sensing technique around since the 1970s prized for its ability to identify chemical and biological molecules in a wide range of fields. It is out in the commercial environment, but not very much since the materials required to perform the sensing end up consumed upon use, relatively expensive and complicated to fabricate.

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Those days may soon end as an international research team led by University at Buffalo engineers developed nanotechnology that promises to make SERS simpler and more affordable.

The photonics advancement aims to improve the ability to detect trace amounts of molecules in diseases, chemical warfare agents, fraudulent paintings, and environmental contaminants.

“The technology we’re developing – a universal substrate for SERS – is a unique and, potentially, revolutionary feature. It allows us to rapidly identify and measure chemical and biological molecules using a broadband nanostructure that traps a wide range of light,” said Qiaoqiang Gan, UB assistant professor of electrical engineering and the study’s lead author.

When a powerful laser interacts chemical and biological molecules, the process can excite vibrational modes of these molecules and produce inelastic scattering, also called Raman scattering, of light. As the beam hits these molecules, it can produce photons that have a different frequency from the laser light. While rich in details, the signal from scattering is weak and difficult to read without a very powerful laser.

SERS addresses the problem by utilizing a nanopatterned substrate that significantly enhances the light field at the surface and, therefore, the Raman scattering intensity. Unfortunately, traditional substrates end up designed for only a very narrow range of wavelengths.

This is problematic because different substrates need to work if scientists want to use a different laser to test the same molecules. In turn, this requires more chemical molecules and substrates, increasing costs and time to perform the test. The universal substrate solves the problem because it can trap a wide range of wavelengths and squeeze them into very small gaps to create a strongly enhanced light field.

The technology consists of a thin film of silver or aluminum that acts as a mirror, and a dielectric layer of silica or alumina. The dielectric separates the mirror with tiny metal nanoparticles randomly spaced at the top of the substrate.

“It acts similar to a skeleton key. Instead of needing all these different substrates to measure Raman signals excited by different wavelengths, you’ll eventually need just one. Just like a skeleton key that opens many doors,” said UB PhD candidate in electrical engineering and team member, Nan Zhang.

“The applications of such a device are far-reaching,” said UB PhD candidate in electrical engineering and team member, Kai Liu. “The ability to detect even smaller amounts of chemical and biological molecules could be helpful with biosensors that are used to detect cancer, Malaria, HIV and other illnesses.”

The technology could improve scientists’ ability to detect trace amounts of toxins in the air, water or other spaces that are causes for health concerns. And it could aid in the detection of chemical weapons.

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