A glass substrate coated with ZnO nanorods via hydrothermal for formaldehyde vapor sensing is reported. The proposed sensor device was characterized against formaldehyde vapor concentrations varied from 1% to 5% with reference point as 0% (pure water) at room temperature. A significant sensing response was observed where the output voltage reduced by 0.0856 V via scattering effect by ZnO nanorods upon exposure to the maximum tested concentration (5%). The sensitivity and linearity of the sensing response were recorded to be approximate value of -0.0168 V/% and 98.06% correspondingly. The sensor device was found to have good measurement stability in measuring as low as 1% of concentration for a prolonged time of 600 s. This proposed sensor has potential applications in monitoring air pollution not only formaldehyde vapor but other harmful and toxic vapors or gases.

A relative humidity sensor was fabricated by exploiting an evanescent wave (EW) on a U-bent tapered plastic optical fiber (POF) coated with zinc oxide (ZnO) nanorods. The POF was tapered manually using a polishing method to a diameter of 0.5 mm, a length of 5 cm, and a radius of 5 cm. ZnO nanorods were synthesized using a hydrothermal method and grown on the POF by a seeding process for 12 h. A significant response of the sensor was observed when the sensor was exposed to 35 to 90%RH due to the intense chemisorption process and changeable relative index in the POF. The sensitivity and resolution of the sensor have been improved by factors of 1.23 and 2.18, respectively, compared to the conventional tapered POF sensor without ZnO coating. Besides, the ZnO-coated sensor also exhibited better repeatability properties in terms of output voltage when exposed to 35 to 90%RH for three repeated measurements. The obtained results revealed that the proposed new POF sensor has an excellent sensing performance as an RH sensor in terms of sensitivity, repeatability, and stability properties.

This paper reported the development of an alcohol sensor based on a glass substrate platform. The glass substrate was coated with two nanomaterial types: Hydroxyethylcellulose/Polyvinylidene fluoride (HEC/PVDF) and Agarose Gel, for comparison purposes. Three layers of coating material have been applied to the glass substrate to obtain the optimum sensing response. The coated glass substrate is kept dry for 24 hours before expose to variations of ethanol concentration to investigate the sensing response. A significant response to alcohol concentrations has been observed for both samples due to the changeable refractive index layer of the coating material. The sensitivity improved by a factor of 1.18 and 1.51, respectively, compared to the bared glass. The proposed sensor employed low-cost and commercially available components such as a glass substrate, LED light source and Arduino microcontroller to perform as an alcohol sensor. It prevents using expensive laser-based sensors, which is less practical in real industrial applications. Based on the experiment results, the HEC/PVDF-coated glass produced has demonstrated better results in terms of repeatability, hysteresis, stability and sensitivity as compared to agarose gel-coated glass. Hence the proposed sensor has a decent potential as an alcohol sensor

This paper described an optimization approach of ZnO nanorods growth duration based on humidity sensing scheme. The proposed structure comprises of silica microfiber integrated with Zinc Oxide (ZnO) nanorods coated glass surface. The silica microfiber was tapered into constant waist diameter of 10 µm using flame brushing technique. The glass surface was grown with ZnO nanorods using hydrothermal method for 6 hours, 9 hours, 12 hours, 15 hours and 18 hours growth time. ZnO nanorods growth time would affect morphological structures such as density which change the light absorption into the nanorods. Samples were exposed to the difference humidity level ranging from 35%RH to 85%RH to observe the change of ZnO refractive index on the glass surface resulting different light attenuation in the silica microfiber. It utilizes the unique features of the scattering and surface absorption capability of the microfiber and ZnO nanomaterials coated glass surface to alter the output light intensity. The reported results may contribute to the optimal ZnO nanorods growth time for humidity sensing application.