Sensing Chip Uses Raman Spectroscopy to Detect Cocaine in Minutes

A chemical sensing chip, developed for use with surface-enhanced Raman spectroscopy (SERS), has demonstrated the ability to detect the chemical fingerprint of cocaine in biological samples. In the future, the technology could be used to detect the presence of other drugs, including marijuana, and could be integrated into a hand-held, portable device for on-site testing.

The chip, which is made with low-cost materials, consists of several layers of material sitting atop one another. A sheet of dielectric material (e.g., silicon dioxide, aluminum oxide, etc.) is sandwiched between a silver mirror, which forms the base of the chip, and a hybrid nanomaterial made from silver (Ag) and gold (Au) nanoparticles. This hybrid nanostructure forms the chip’s active surface.

The surface of the chip traps light at the edges of the Ag and Au nanoparticles. When biological or chemical molecules fall into the tiny spaces between the nanoparticles on the chip’s surface, some of the captured light interacts with the molecules and is scattered. The scattering occurs in recognizable patterns that act as chemical fingerprints, revealing information about what compounds are present.

A scanning electron microscope image shows the surface of a new chemical sensing chip. The surface consists of gold nanoparticles (small bright dots) that have been deposited over silver nanoparticles (light gray regions) to form a hybrid gold-silver nanostructure. Courtesy of Nan Zhang.

When the nanostructure is exposed to light for testing, the silver mirror and the dielectric layer act as an optical cavity, manipulating the photons so that there are a larger number of photons at the surface of the chip. This intensifies the scattering signature of any compounds that are being sensed.

Because all chemicals, including cocaine, opioids, and active ingredients in marijuana, have unique light-scattering signatures, the technology could be used to quickly identify a wide range of chemicals and could one day lead to portable drug detectors.

The technology was developed by researchers at the University of Buffalo and Fudan University in Shanghai, China.

“The high-performance chip we designed was able to detect cocaine within minutes in our experiments. It’s also inexpensive," said professor Qiaoqiang Gan. "It can be produced using raw materials that cost around 10 cents, and the fabrication techniques we used are also low-cost,”

The technology has a long shelf life, with researchers finding that it performed well after a year in an ambient storage environment. The chip’s reliability is due in part to its surface design: The gold nanoparticles, which are deposited last, help to shield the silver nanoparticles from the air, which prevents oxidization, degradation, and tarnishing.

“With our structure, we can realize both high performance and stable performance over time,” Gan said.

The next step in the research is to install the chip in a simple, portable testing device. This technology would first run blood, breath, urine, or saliva through a purification process that extracts specific molecules, such as cocaine or other drugs. Then, any chemicals captured through this procedure would be transferred to the chip for detection and identification.

While SERS is not new, the chip developed by the research team is notable for its performance and low cost.

“SERS holds a lot of promise for rapid detection of drugs and other chemicals, but the materials required to perform the sensing are usually quite expensive,” said researcher Nan Zhang. “The chips used for SERS are typically fabricated using expensive methods such as lithography, which creates specific patterns on a metal substrate. We created our chip by depositing various thin layers of materials on a glass substrate, which is cost-effective and suitable for industrial-scale production."

The research was published in Small Methods (doi:10.1002/smtd.201800045).