Resonance frequency shift of a zinc oxide-(ZnO-) functionalized microcantilever as a response to carbon monoxide (CO) gas has been investigated. Here, ZnO microrods were grown on the microcantilever surface by a hydrothermal method. The measurement of resonance frequency of the microcantilever vibrations due to the gas was carried out in two conditions, that is, gas flow with and without air pumping into an experiment chamber. The results show that the resonance frequency of the ZnO-functionalized microcantilever decreases because of CO in air pumping condition, while it increases when CO is introduced without air pumping. Such change in the resonance frequency is influenced by water vapor condition, and a possible model based on water-CO combination was proposed.

Microcantilever-based sensors have attracted interest in the last decade because of their small size, rapid detection and high sensitivity. This sensor can be applied in the many fields, i.e. physics, chemistry, biology, biochemistry, medical, and environment. In this paper, we describe microcantilever-based sensor for environmental monitoring, especially for a humidity detection. This sensor was operated in dynamic mode where a change in mass or spring constant of the microcantilever provides the resonance frequency change. Here, a change of humidity is detected by the resonance frequency and the amplitude changes. It is found that the increase in the humidity causes the decreasing the resonance frequency but increasing the amplitude. This result opens up the possibility of the humidity detection using microcantilever-based sensor.

A microcantilever (MC) coated by Al-doped ZnO nanorods (AZNRs) was used for carbon monoxide (CO) detection at ambient temperature. Very high sensitivity (on the order of femtograms) was obtained, which is caused by the intense adsorption of CO molecules on the AZNR surface. After the samples had been prepared and characterized, the effects of the presence of water vapor on the CO detection were investigated. Although no response was obtained for AZNRs without the presence of water vapor (i.e. under a vacuum), high sensitivity was observed in the presence of water vapor (finite humidity). Regarding the above phenomena, we propose a model that is a replacement process of the water vapor molecules by the CO molecules on the AZNR surface and discuss it in detail.