May 15 2018
Imagine testing for marijuana, opioids, and cocaine as rapidly as a breathalyzer tests alcohol. An innovative, less expensive chemical sensing chip enables getting a step closer to this technology, which has been on the wish list of not only police officers but also others for monitoring drug use and curbing high-risk driving.
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. (Image credit: Nan Zhang)
The chip can be incorporated into a portable, handheld device for the detection of drugs in biological samples such as spit, urine, breath, or blood.
Currently, there is a great demand for on-site drug testing. 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.
Qiaoqiang Gan, Ph.D, Associate Professor of Electrical Engineering in the University at Buffalo School of Engineering & Applied Sciences
“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 innovative chip was developed by Gan in collaboration with first authors Jun Gao, a research associate of Material Sciences at Fudan University in China, and Nan Zhang, a PhD candidate at UB, together with colleagues from the UB Department of Electrical Engineering; the UB Research Institute on Addictions; and the UB Department of Community Health and Health Behavior in the UB School of Public Health and Health Professions.
The National Science Foundation funded the study, which was reported in the Small Methods journal on May 7, 2018.
Detecting the Chemical Fingerprint of Cocaine & Other Drugs
The innovative chip is an engineered nanostructure with the ability to capture light at the edges of silver and gold nanoparticles. In case chemical or biological molecules end up on the surface of the chip, a portion of the trapped light interacts with the molecules and is “scattered” into light of new energies. This effect takes place in discernible patterns that function as fingerprints, providing information related to the existing compounds.
Since all chemicals - such as opioids, cocaine, and active ingredients in marijuana—have their distinctive light-scattering patterns, this technology can be used by scientists to rapidly identify a broad range of chemicals.
This sensing technique is known as surface-enhanced Raman spectroscopy (SERS) and is already well-known. However, the chip developed by Gan and his team is remarkable with respect to its higher performance and lesser 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. 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.
Nan Zhang, a PhD candidate at UB
An Optical Layer Cake
The innovative chip, which is a structure called a metasurface, looks like a layer cake, including multiple horizontal material layers formed on top of one another.
Particularly, the technology involves sandwiching a sheet of dielectric material (e.g. aluminum oxide, silicon dioxide, etc.) between a silver mirror (the chip’s base) and a hybrid nanomaterial made of silver and gold nanoparticles (the active surface of the chip).
This structure is best suited for SERS: molecules of cocaine or other substances fill the minute spaces between the nanoparticles on the surface of the chip. Subsequently, while exposing the structure to light for testing, the dielectric layer and the silver mirror function as an “optical cavity,” controlling light such that the number of photons at the chip’s surface is increased. Eventually, the scattering pattern of compounds being tested is intensified, thereby enhancing detection.
The shelf life of this technology is long; scientists found out that it worked well after being stored for a year. The durability of the chip is partly due to its surface design: the lastly deposited gold nanoparticles help in shielding the silver nanoparticles from air, thereby preventing oxidization, degradation, and tarnishing.
“With our structure, we can realize both high performance and stable performance over time,” stated Gan.
The next stage in this study is the incorporation of the chip into a simple, portable testing device. Initially, this technology would run saliva, urine, breath, or blood through a purification process in which specific molecules, such as cocaine or other drugs, are extracted. Subsequently, any chemicals captured in this process would be moved to the chip for detection and identification.