SERS Chip Senses Near the Quantum Limit

University at Buffalo researchers have developed a chemical sensing chip that boasts a range of potential applications, from the detection of illicit substances and dangerous materials, to counterfeit prevention. The chip, which relies on surface-enhanced Raman spectroscopy (SERS), supports incorporation into hand-held sensor devices and approached quantum-limit sensing capabilities — a challenge for many conventional SERS chips — in testing.

Qiaocqiang Gan, a professor of electrical engineering, led the team that introduced the chip. The team’s work builds on a previous advance, in which scientists in Gan’s laboratory created a chip that demonstrated the ability to trap light at the edges of gold and silver nanoparticles. Because the metals were unevenly spaced in that design, however, it was difficult to implement the chip for the identification of individually scattered molecules, especially those that appeared at different locations of the chip.

When located on the surface of the chip, biological and/or chemical molecules interacted with portions of the scattered light, resulting in light that exhibited different energy than that which the light itself initially possessed. The phenomenon occurs in patterns that distinguish individual molecules and deliver information about the compounds that are and are not present.

The chip, which also may have uses in food safety monitoring, anti-counterfeiting, and other fields where trace chemicals are analyzed. Courtesy of Huaxiu Chen, University at Buffalo.

An individual chemical’s light scattering signature is not replicated in other chemicals, meaning the scattering technology could be used in hand-held devices to detect, for example, drugs in blood, breath, urine, and other biological samples.

The method, SERS, is additionally used in food-safety monitoring and quality assurance, as well as pollution monitoring and control.

Working from its earlier design, the Gan-led team applied four molecules of different lengths — BZT, 4-MBA, BPT, and TPT — to the fabrication process, aimed at controlling the size of the physical gaps between the gold and silver nanoparticles.

'There is a great need for portable and cost-effective chemical sensors in many areas, especially drug abuse,' said Qiaoqiang Gan, professor of electrical engineering. Courtesy of the University at Buffalo.

Fabrication itself was based on the processes of atomic layer deposition and self-assembled monolayers. A commonly used fabrication method for working in tandem with SERS is electron-beam lithography, the researchers said.

The resulting SERS chip exhibited strong uniformity in a cost-effective design/production process.

“We think the chip will have many uses in addition to hand-held drug detection devices,” said Nan Zhang, a postdoctoral researcher in Gan’s lab and lead author on the work. Zhang said the chip could additionally benefit applications in the security and defense sectors, as well as health care.

Researchers from the University of Shanghai for Science and Technology, in China, and KAUST (King Abdullah University of Science and Technology), in Saudi Arabia, contributed to the latest work.

The U.S. National Science Foundation supported the research, which was published in Advanced Optical Materials (www.doi.org/10.1002/adom.202001634).