Abstract
An oscillating piezoresistive microcantilever (MC) coated with an aluminum (Al)-doped zinc oxide (ZnO) nanorods was used to detect carbon monoxide (CO) in air at room temperature. Al-doped ZnO nanorods were grown on the MC surface using the hydrothermal method, and a response to CO gas was observed by measuring a resonant frequency shift of vibrated MC. CO gas response showed a significant increase in resonant frequency, where sensitivity in the order of picogram amounts was obtained. An increase in resonant frequency was also observed with increasing gas flow rate, which was simultaneously followed by a decrease in relative humidity, indicating that the molecular interface between ZnO and H2O plays a key role in CO absorption. The detection of other gases of carbon compounds such as CO2 and CH4 was also performed; the sensitivity of CO was found to be higher than those gases. The results demonstrate the reversibility and reproducibility of the proposed technique, opening up future developments of highly sensitive CO-gas detectors with a fast response and room temperature operation.
Highlights
Microcantilever (MC) sensors are MEMS devices used to detect chemical, physical, and biological objects with high sensitivity, rapid response, and operation at room temperature [1,2,3]
The vibration amplitude vs frequency profile of the Al-doped zinc oxide (ZnO) nanorod-coated MC can be seen in Figure 2d, showing the resonant frequency of 29.91 kHz
Since the MC was operating in dynamic mode, the vibration of the cantilever was activated by applying AC voltage to the piezoelectric generated by a microcontroller-controlled direct digital synthesizer (DDS) [12]
Summary
Microcantilever (MC) sensors are MEMS (microelectrochemical system) devices used to detect chemical, physical, and biological objects with high sensitivity, rapid response, and operation at room temperature [1,2,3]. The working principle of this sensor is based on a deflection of the MC due to an object becoming attached to its surface (static mode), or a resonant frequency change of the vibrated. Carbon monoxide (CO) gas, which is an odorless, colorless, tasteless, and toxic compound, has been successfully detected using the MC coated with sensitive layers of poly(ethylene oxide)/Ni acetate (PEO/NiA) [8], Fe(III) porphyrin [9], and zinc oxide (ZnO) layers [11,12]. Kooser et al reported CO detection by PEO/NiA-coated MC, where for Sensors 2020, 20, 2013; doi:10.3390/s20072013 www.mdpi.com/journal/sensors
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