This model, created at Rice University, illustrates charge distribution in glucose. The light blue region shows the electron cloud distribution in a single glucose molecule. The purple regions show the drastic charge redistribution when anchored to Janus MoSSE and detected via surface-enhanced Raman spectroscopy. Image: Lou Group/Rice University.
This model, created at Rice University, illustrates charge distribution in glucose. The light blue region shows the electron cloud distribution in a single glucose molecule. The purple regions show the drastic charge redistribution when anchored to Janus MoSSE and detected via surface-enhanced Raman spectroscopy. Image: Lou Group/Rice University.

A sandwich of molybdenum, sulfur and selenium (MoSSe) turns out to be deliciously useful for detecting biomolecules. Tests of a two-dimensional (2D) Janus compound at Rice University's Brown School of Engineering showed it could make an effective and universal platform for improving the detection of biomolecules via surface-enhanced Raman spectroscopy (SERS).

Using glucose to test the material proved its ability to boost the Raman enhancement factor by more than 100,000 times, which the researchers say is comparable to the highest-reported enhancement factor for 2D substrates. The Rice researchers report their work in a paper in Nanoscale.

SERS is an established technique that allows the detection and identification of small concentrations of molecules – or even single 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. In contrast, the Janus MoSSe synthesized at Rice is non-metallic. "This work mainly addresses whether we can enhance the target molecules' signal strength," said materials scientist and principal investigator Jun Lou. "We wanted to know if we could make it stand out from the background noise."

Introduced by the Lou lab in 2017, MoSSe is 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 different electronegativities of each layer make it a SERS superstar, said lead author and Rice alumnus Shuai Jia, a former graduate student in Lou's lab. "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," he explained. This 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 still room for improvement. "We're looking at hybrids of MoSSe with some metallic nanoparticles, and also trying to enhance the dipole strength," he said.

This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.