Volatile organic compounds are substances that are released as gases and can be harmful to one’s health. They are often found in paints, medications, and refrigerants, among other common items, but they can also act as indicators of explosives, insect infestation, food deterioration, and disease.
E-noses combine arrays of chemical sensors with pattern recognition techniques to recognize odors. Image Credit: Hu, W., Wan, L., Jian, Y., Ren, C., Jin, K., Su, X., Bai, X., Haick, H., Yao, M., Wu, W., Adv. Mater. Technol. 2019, 4, 1800488. https://doi.org/10.1002/admt.201800488
Tracing VOCs is critical for public safety and other “smell” concerns. To that aim, Liu et al. published in AIP Publishing’s Applied Physics Reviews a fluid mechanics-based chamber design for an electronic nose (e-nose) that reliably detects VOCs at low concentrations.
The method, which includes utilizing a shunt-like device to control fluid flow behavior, is a step ahead in developing e-nose technology.
In terms of selectivity, sensitivity, repeatability, and stability, methods for detecting VOCs encounter several difficulties. E-noses, modeled after the olfactory system, can get over some of these obstacles by integrating arrays of chemical sensors with methods for pattern recognition.
However, when the sensor is placed in various locations inside the “nose” chamber, several e-noses provide distinct signals for VOCs with the same concentration.
To counteract this problem, the fluidic behavior 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.
Weiwei Wu, Interdisciplinary Research Center of Smart Sensors, School of Advanced Materials and Nanotechnology, Xidian University
A vertical chamber that closely resembles a showerhead was part of the original e-nose design. As gas flows around to uniformly spaced sensors via holes in the device’s bottom, this encourages vertical flow.
The researchers improved the volume, symmetry, hole position, and sensor location of their e-nose chamber using fluid mechanics models. To encourage fluid flow and speed up response time, they incorporated a device resembling a shunt.
The researchers created a Teflon chamber and tested the e-nose’s sensing capabilities based on the outcomes of their simulation. Two chambers, one with the shunt and one without, were compared. Sensing an example VOC consistently worked 1.3 times better in the chamber with the shunt device.
The authors want to reduce reaction and recovery time in the future by decreasing the chamber and making the structure even better.
Wu added, “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.”
Journal Reference:
Liu, T., et al. (2023) Controlling fluidic behavior for ultra-sensitive volatile sensing. Applied Physics Reviews. doi:10.1063/5.0141840.