Nanotechnology Could Make Molecule-identifying Spectroscopy More Practical
The interest generated by surface-enhanced Raman spectroscopy (SERS) has been matched by few sensing techniques. And industry’s need for more powerful sensors is ever growing, from airport security detecting explosives to art historians authenticating paintings.
Pioneered in the 1970s, SERS is a sensing technique highly valued for its capability to identify chemical and biological molecules in a wide range of fields.
It has been commercialized, though not broadly. This is because the materials needed to perform the sensing are consumed upon use, relatively expensive and complicated to fabricate.
But all those roadblocks may soon disappear.
Nanotechnology that promises to make SERS simpler and more affordable has been developed by an international research team led by University at Buffalo engineers.
Universal SERS Substrate
Detailed in a recent research paper, the photonics advancement aims to improve our ability to detect trace amounts of molecules in diseases, environmental contaminants, chemical warfare agents, fraudulent artworks and more.
“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 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 an extremely powerful laser.
SERS solves the problem by using a nanopatterned substrate that significantly enhances the light field at the surface and, therefore, the Raman scattering intensity. Unfortunately, traditional substrates are typically designed for only a very narrow range of wavelengths.
This is problematic since different substrates are needed 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.
“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,” Zhang said.
“The applications of such a device are far-reaching,” said 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.”
Illustration: New SERS approach is 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. Credit: Qiaoqiang Gan.