Nanoparticle Design and Assembly for p-type Metal Oxide Gas Sensors

Metal oxide semiconductors have wide band gaps with tailorable electrical properties and high stability, suitable for chemiresistive gas sensors. p-Type oxide semiconductors generally have less sensitivity than n-type counterparts but...

Acetone Sensing and Catalytic Conversion by Pd-Loaded SnO2

Noble metal additives are widely used to improve the performance of metal oxide gas sensors, most prominently with palladium on tin oxide. Here, we photodeposit different quantities of Pd (0–3 mol%) onto nanostructured SnO2 and determine their effect on sensing acetone, a critical tracer of lipolysis by breath analysis. We focus on understanding the effect of operating temperature on acetone sensing performance (sensitivity and response/recovery times) and its relationship to catalytic oxidation of acetone through a packed bed of such Pd-loaded SnO2. The addition of Pd can either boost or deteriorate the sensing performance, depending on its loading and operating temperature. The sensor performance is optimal at Pd loadings of less than 0.2 mol% and operating temperatures of 200–262.5 °C, where acetone conversion is around 50%.

Development of a Low-Cost Electronic Nose for Detection of Pathogenic Fungi and Applying It to Fusarium oxysporum and Rhizoctonia solani

Electronic noses can be applied as a rapid, cost-effective option for several applications. This paper presents the results of measurements of samples of two pathogenic fungi, Fusarium oxysporum and Rhizoctonia solani, performed using two constructions of a low-cost electronic nose. The first electronic nose used six non-specific Figaro Inc. metal oxide gas sensors. The second one used ten sensors from only two models (TGS 2602 and TGS 2603) operating at different heater voltages. Sets of features describing the shapes of the measurement curves of the sensors’ responses when exposed to the odours were extracted. Machine learning classification models using the logistic regression method were created. We demonstrated the possibility of applying the low-cost electronic nose data to differentiate between the two studied species of fungi with acceptable accuracy. Improved classification performance could be obtained, mainly for measurements using TGS 2603 sensors operating at different voltage conditions.

Nanostructured Gas Sensors: From Air Quality and Environmental Monitoring to Healthcare and Medical Applications

In the last decades, nanomaterials have emerged as multifunctional building blocks for the development of next generation sensing technologies for a wide range of industrial sectors including the food industry, environment monitoring, public security, and agricultural production. The use of advanced nanosensing technologies, particularly nanostructured metal-oxide gas sensors, is a promising technique for monitoring low concentrations of gases in complex gas mixtures. However, their poor conductivity and lack of selectivity at room temperature are key barriers to their practical implementation in real world applications. Here, we provide a review of the fundamental mechanisms that have been successfully implemented for reducing the operating temperature of nanostructured materials for low and room temperature gas sensing. The latest advances in the design of efficient architecture for the fabrication of highly performing nanostructured gas sensing technologies for environmental and health monitoring is reviewed in detail. This review is concluded by summarizing achievements and standing challenges with the aim to provide directions for future research in the design and development of low and room temperature nanostructured gas sensing technologies.

The UV Effect on the Chemiresistive Response of ZnO Nanostructures to Isopropanol and Benzene at PPM Concentrations in Mixture with Dry and Wet Air

Towards the development of low-power miniature gas detectors, there is a high interest in the research of light-activated metal oxide gas sensors capable to operate at room temperature (RT). Herein, we study ZnO nanostructures grown by the electrochemical deposition method over Si/SiO2 substrates equipped by multiple Pt electrodes to serve as on-chip gas monitors and thoroughly estimate its chemiresistive performance upon exposing to two model VOCs, isopropanol and benzene, in a wide operating temperature range, from RT to 350 °C, and LED-powered UV illumination, 380 nm wavelength; the dry air and humid-enriched, 50 rel. %, air are employed as a background. We show that the UV activation allows one to get a distinctive chemiresistive signal of the ZnO sensor to isopropanol at RT regardless of the interfering presence of H2O vapors. On the contrary, the benzene vapors do not react with UV-illuminated ZnO at RT under dry air while the humidity’s appearance gives an opportunity to detect this gas. Still, both VOCs are well detected by the ZnO sensor under heating at a 200–350 °C range independently on additional UV exciting. We employ quantum chemical calculations to explain the differences between these two VOCs’ interactions with ZnO surface by a remarkable distinction of the binding energies characterizing single molecules, which is −0.44 eV in the case of isopropanol and −3.67 eV in the case of benzene. The full covering of a ZnO supercell by H2O molecules taken for the effect’s estimation shifts the binding energies to −0.50 eV and −0.72 eV, respectively. This theory insight supports the experimental observation that benzene could not react with ZnO surface at RT under employed LED UV without humidity’s presence, indifference to isopropanol.