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Development of sensors for improved moisture control

Researchers have designed a low-cost, stable and responsive sensor with the ability to provide moisture control for manufacturing and storage.

Fuke Wang and colleagues from the Singapore Institute of Materials Research and Engineering, A*STAR have developed an optical humidity sensor that exploits the unique properties of ultrathin layers of graphene oxide (GO) films.

The humidity levels of ambient air can have a significant effect on human comfort and health; it can also impact many manufacturing processes and is detrimental to the quality of stored goods.

“Our research shows for the first time that atomic-scale GO can be used for colorimetric humidity sensors,” said Wang.

“Due to the atomic properties of GO and their hygroscopic nature, the sensor is highly efficient and faster-responding compared with current sensor technologies.”

Unlike most humidity sensors, which are electronic and require a power supply, GO-based colorimetric sensors respond to humidity levels by changing to a colour that can be easily observed. For greater accuracy, the change in colour can be quantitatively measured by analysing the reflection spectra of the sensor. Because the GO sensor operates at the atomic level, it can rapidly respond to moisture changes.

Exploiting the atomic properties of GOs can only occur if films of uniform thickness can be fabricated; thickness influences the response time and uniformity determines the quality of the sensor.

The research team overcame this challenge by using a process in which a substrate is dipped in and out of a solution at a constant speed.

“We focused on optimising the solution viscosity, the substrate-surface treatment and the dip-coating conditions,” said Wang.

“This showed that we can now easily control the thickness of uniform films of GO with a process that is scalable and also generates zero waste.”

The low-cost, non-toxicity and rapid response of GO sensors makes them desirable as disposable sensors. They can be incorporated into food packaging, where humidity levels need to be strictly controlled for storage, for medical instrumentation and semiconducting device manufacturing and storage, as well as environmental monitoring. Their disposal also has no environmental impact.

“We are now exploring further increases in efficiency and sensitivity, and the application to other vapors and gases,” said Wang.

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