The device consists of a digital camera, a laser, imaging optics, a signal generator, digital signal processing and other components that can detect tiny amounts of substances in the air.
Researchers believe this new “sniffer” will achieve a detection level that approaches the theoretical limit, surpassing other state-of-the-art chemical sensors. The implications could be significant for anyone whose job is to detect explosives, biological agents and narcotics.
“While the research community has been avoiding the nonlinearity associated with the nanoscale mechanical oscillators, we are embracing it,” says co-developer Nickolay Lavrik, a researcher in the CNMS. “In the end, we hope to have a device capable of detecting incredibly small amounts of explosives compared to today’s chemical sensors.”
The approach makes use of microcantilevers similar to those used in atomic force microscopy. The microcanilevers serve as microresonators that measure changes in the resonance frequency due to mass changes. Although the concept is relatively simple, assembling a working model is more difficult.
“These challenges are due to requirements of measuring and analyzing tiny oscillation amplitudes that are about the size of a hydrogen atom,” Lavrik reports. He says previous approaches would have required sophisticated low-noise electronic components such as lock-in amplifiers and phase-locked loops, which add cost and complexity.
This new type of sniffer works by deliberately hitting the microcantilevers with relatively large amounts of energy associated with a range of frequencies, forcing them into wide oscillation.
“In the past, people wanted to avoid this high amplitude because of the high distortion associated with that type of response,” says ORNL’s Panos Datskos, a member of the Measurement Science and Systems Engineering Division. “But now we can exploit that response by tuning the system to a very specific frequency that is associated with the specific chemical or compound we want to detect.”
When the target chemical reacts with the microcantilever, it shifts the frequency depending on the weight of the compound, thereby providing the detection.
“With this new approach, when the microcantilever stops oscillating we know with high certainty that the target chemical or compound is present,” Lavrik says.
The researchers envision this technology being incorporated in a handheld instrument that could be used by transportation security screeners, law enforcement officials and the military. Other potential applications are in biomedicine, environmental science, homeland security and analytical chemistry.