New Ultra-Thin, Highly Sensitive Sensor to Detect Low Humidity Levels

By David J. CrossOct 21 2021Reviewed by Bethan Davies

Traditional sensor systems are inadequate when it comes to measuring low water vapor content in air. However, physicists at the Yuri Gagarin Technical University in Saratov, Russia (SSTU), and the University of Duisburg-Essen (UDE) have developed an innovative kind of sensor to help overcome this issue.

Monitoring air quality is an important focal point in many areas, and the ability to measure humidity plays into this. This is as important indoors as it is outdoors, as certain environments such as biomedical or electronics laboratories have stringent ambient air requirements. The ability to manage and control indoor ambient conditions, including humidity and temperature, is therefore crucial.

While there are a range of dynamic humidity sensors built into certain commercial instruments fit for monitoring ambient conditions, they lack the capacity to identify water vapor concentrations lower than 50 ppm: in other words, less than 0.3% relative humidity. Therefore, while they may be powerful, these sensors may not be appropriate for all applications.

Selective Detection of Humidity in Air

The team of researchers from UDE and SSTU took to the challenge by approaching humidity sensing with an entirely novel strategy. The physicists designed sensors using Molybedium Carbide (MXenes), a 2D nanomaterial that has the capacity to detect trace amounts of water molecules that come into contact with their surface.

In this way, the sensor performance improves enormously—the detection limit is pushed far below the previous state of the art. More is really not possible. 

Dr. Hanna Pazniak, UDE experimental physicist

MXenes, or Mo₂CT_x, are highly conductive materials that can be used for the enhanced selective detection of humidity in air. What that means, is they have extremely good sensing capabilities with fast response times and detection limits in the range of 30 ppm.¹

Consisting of or transition metal nitrides or compounds of transition metal carbides, the materials are piled up in layers but still remain just a few atoms thick. The benefit of this technique and piling method means that sensors can be extremely sensitive and ultra-thin.

They detect water vapors down to 10 ppm, or 0.06 percent relative humidity. That's the lowest value known so far.

Dr. Hanna Pazniak, UDE experimental physicist

Enhanced Capabilities

The team discovered that the study showed promising signs when employing 2D MXene flakes and that humidity vapors enhance the resistance of the poly flake Mo₂CT_x layer. Moreover, this allows the reversible detection of water vapors in the air to around 10 ppm, demonstrating better detecting limits than today’s commercially available devices.

These enhanced capacities for the selective detection of humidity in the air show that the team made a significant stride in approaching the limitations of current methods. The sensors also come with the added benefit that it is possible to upscale the materials for mass production.

What’s more, is the team has stated that the sensors are also capable of detecting a range of different vapors – as well as water – including ammonia, alcohols and ketones all less than 100 ppm.

The sensors can also be calibrated in various ways and due to the selectivity to different vapors, can be fitted into a specially designed on-chip multisensory for other applications.² This could offer other lab teams greater control over ambient conditions as well as demonstrate a material with multi-functional capabilities.

With the potential of having such a sensing tool, researchers across various fields from biomedical applications or microelectronics can rest assured ambient conditions in the lab are carefully monitored.

References and Further Reading

Pazniak, H., Et. Al. (2021) 2D Molybdenum Carbide MXenes for Enhanced Selective Detection of Humidity in Air. [Online] Advanced Materials, Available at: https://doi.org/10.1002/adma.202104878

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