Engineers Adapt 2D 'Sandwich' for Surface-Enhanced Raman Spectroscopy

Tests at Rice University’s Brown School of Engineering of a two-dimensional Janus compound showed it could be an effective and universal platform for improving the detection of biomolecules via surface-enhanced Raman spectroscopy (SERS).

Monolayer Janus MoSSe, a compound of molybdenum, sulfur, and selenium developed at Rice University, is adept at detecting biomolecules via surface-enhanced Raman spectroscopy. Its nonmetallic nature helps by curtailing background noise in the signal. Courtesy of Lou Group/Rice University.

Using glucose to test the material proved its ability to boost its Raman enhancement factor by more than 100,000 times, which the researchers say is comparable to the highest-reported enhancement factor for 2D substrates.

SERS is an established technique that enables the detection and identification of small concentrations of molecules that get close to or adsorbed by metallic surfaces, including nanoparticles. It’s often used to detect nanoscale proteins in bodily fluids, helping to detect diseases and determine treatments, and in environmental analysis.

But metallic SERS media often prompt side reactions that create background noise. Janus MoSSe synthesized at Rice is nonmetallic. “This work mainly addresses whether we can enhance the target molecules’ signal strength,” said Jun Lou, materials scientist and principal investigator. “We wanted to know if we could make it stand out from the background noise.”

MoSSe, introduced by the Lou lab in 2017, was produced by chemical vapor deposition. Molybdenum sits in the middle with a layer of sulfur on one side and another of selenium on the other; hence the two-faced Janus characterization.

“The dipole created between the top sulfur and the bottom selenium lands out-of-plane, and this creates an electrical field a few nanometers beyond the MoSSe,” said lead author and Rice alumnus Shuai Jia, a former graduate student in Lou’s lab. That field interacts with molecules that come close, enhancing their vibrational intensity enough to be detected.

The researchers noted that tests with MoSSe also detected molecules of the neurotransmitter dopamine and that the substrate should be adaptable to sense other molecules.

Lou said there’s room for improvement. “We’re looking at hybrids of MoSSe with some metallic nanoparticles, and also trying to enhance the dipole strength,” he said.

The research was published in Nanoscale (www.doi.org/10.1039/D0NR00300J).