E-nose to sniff out volatile organic compounds

Researchers have introduced a fluid mechanics-based chamber design for an electronic nose (e-nose) that consistently detects volatile organic compounds (VOCs) at low concentrations. VOCs are chemicals emitted as gases that can have adverse health effects. They are often found in paints, pharmaceuticals and refrigerants, among other common products, but they can also act as markers of explosives, insect infestations, food spoilage and disease. Tracing VOCs is important for public safety and ‘smell’-related issues.

The new strategy to detect VOCs is a step forward in e-nose technology development. Methods for detecting VOCs face many challenges in terms of selectivity, sensitivity, reproducibility and stability. E-noses, inspired by the olfactory system, can overcome some of these barriers by combining arrays of chemical sensors with pattern recognition techniques to recognise odours. However, many e-noses generate different signals toward VOCs of the same concentration when the sensor is located in different parts of the ‘nose’ chamber.

Researcher and author Weiwei Wu said that in order to counteract this problem, the fluidic behaviour of the gas flow needs to be well controlled. “This ensures a uniform fluidic field and concentration of VOCs in the chamber and avoids generating any fake sensing characteristics,” Wu said.

The starting e-nose design featured a vertical chamber that looks much like a showerhead. This promotes vertical flow as gas spreads through holes at the bottom of the device and around to evenly distributed sensors. Using fluid mechanics simulations, the researchers optimised the volume, symmetry, sensor location and hole location of the e-nose chamber. They also added a shunt-like device to promote fluid flow and shorten response time.

Based on their simulation results, the researchers fabricated a Teflon chamber and measured the sensing performance of their e-nose. They compared two chambers, one with the shunt and one without; the chamber with the shunt consistently performed around 1.3 times better at sensing an example VOC. The authors plan to focus on minimising the chamber and improving the structure further to decrease response and recovery time.

“E-nose research is a highly interdisciplinary field. Chemists, physicists, biologists, electronics engineers, and data scientists need to work together to solve issues including effective sensing that considers the fundamental mechanisms of absorption/desorption, algorithms that achieve precise recognition of VOCs more quickly and with lower energy consumption, and how new technologies, such as memristors, should be involved,” Wu said.

The research findings were published in Applied Physics Reviews.

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