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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. Credit: Nan Zhang

A team from the University of Buffalo has developed a chemical sensing chip that could one day yield a portable drug detector.

To create the chip, the researchers engineered a nanostructured chip that traps light at the edges of gold and silver nanoparticles, so that when biological or chemical molecules land on its surface, some of the captured light interacts with the molecules and is scattered into light of new energies.

This effect occurs in recognizable patterns that act as fingerprints, revealing information about what compounds are present.

The chip contains a sheet of dielectric material like silicon dioxide or aluminum oxide, sandwiched between a silver mirror and a hybrid nanomaterial made from gold and silver nanoparticles.

The architecture of the chip allows molecules of cocaine or other substances to fall into the tiny spaces between the nanoparticles on the chip’s surface.

After the structure is exposed to light for testing, the silver mirror and the dielectric layer act as an optical cavity that manipulates the light in a way that increases the number of photons at the surface of the chip, intensifying the scattering signature of compounds being sensed to improve detection.

The researchers believe that the new chip could be integrated into a handheld, portable device that can detect drugs in biological samples including blood, breath, urine or spit because all chemicals—including cocaine, opioids and active ingredients in marijuana—contain unique light-scattering signatures.

“Currently, there is a great demand for on-site drug testing,” Qiaoqiang Gan, PhD, associate professor of electrical engineering in the University at Buffalo School of Engineering and Applied Sciences, said in a statement. “The high-performance chip we designed was able to detect cocaine within minutes in our experiments. It's also inexpensive: It can be produced using raw materials that cost around 10 cents, and the fabrication techniques we used are also low-cost.

“In the future, we are hoping to also use this technology to detect other drugs, including marijuana,” he added. “The widening legalization of marijuana raises a lot of societal issues, including the need for a system to quickly test drivers for drug use.”

The researchers used a sensing method called surface-enhanced Raman spectroscopy (SERS).

“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,” Nan Zhang, a PhD candidate at Buffalo, said in a statement. “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 team will now look to install the chip in a simple, portable testing device.

The study was published in Small Methods.

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