Nanotechnology improves molecule-identifying spectroscopy

An international research team led by University at Buffalo engineers has developed nanotechnology that promises to make surface-enhanced Raman spectroscopy (SERS) simpler and more affordable.

SERS is a sensing technique lauded for its ability to identify chemical and biological molecules in a range of fields. It has been commercialised but the materials required to perform the sensing are consumed upon use, making the technique relatively expensive and corresponding systems complicated to fabricate.

“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 lead author of a paper on the study that is published in Advanced Materials Interfaces.

Additional authors of the study are: UB PhD candidates in electrical engineering Nan Zhang, Kai Liu, Haomin Song, Xie Zeng, Dengxin Ji and Alec Cheney; and Suhua Jiang, associate professor of materials science, and Zhejun Liu, PhD candidate, both at Fudan University in China.

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

SERS addresses the problem by utilising a nanopatterned substrate that enhances the light field at the surface and, therefore, the Raman scattering intensity. Drawbacks occur, however, because traditional substrates are typically designed for a very narrow range of wavelengths.

This is problematic because 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 is claimed to solve the problem because it can trap a wide range of wavelengths and compress them into very small gaps to create a strongly enhanced light field.

According to UB, the technology consists of a thin film of silver or aluminium that acts as a mirror, and a dielectric layer of silica or alumina. The dielectric separates the mirror with 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,” Zhang said in a statement.

“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.”

The US National Science Foundation supported the research in a grant to develop a real-time in-vivo biosensing system.