The Effect of Rare Earths on the Response of Photo UV-Activate ZnO Gas Sensors.

In this work, ZnO nanoparticle resistive sensors decorated with rare earths (REs; including Er, Tb, Eu and Dy) were used at room temperature to detect atmospheric pollutant gases (NO2, CO and CH4). Sensitive films were prepared by drop casting from aqueous solutions of ZnO nanoparticles (NPs) and trivalent RE ions. The sensors were continuously illuminated by ultraviolet light during the detection processes. The effect of photoactivation of the sensitive films was studied, as well as the influence of humidity on the response of the sensors to polluting gases. Comparative studies on the detection properties of the sensors showed how the presence of REs increased the response to the gases detected. Low concentrations of pollutant gases (50 ppb NO2, 1 ppm CO and 3 ppm CH4) were detected at room temperature. The detection mechanisms were then discussed in terms of the possible oxidation-reduction (redox) reaction in both dry and humid air atmospheres.

Different dry hopping and fermentation methods: influence on beer nutritional quality.

BACKGROUND: Nowadays, the craft beer market is booming and the consumer trend for trying something new is increasing. Here, nine different treatments of a craft beer were realized in a pilot plant, studying fermentation and dry-hopping types. Quality parameters of the beer such as polyphenols, antioxidants, bitterness, colour and alcohol were analysed. In addition, an electronic nose was used to distinguish beer types. RESULTS: Results showed that dry hopping in maturation with warm temperature increased the bitterness from 33 to 40 IBUs. The treatment using two yeasts and two fermentation temperatures resulted in the highest antioxidant capacity of the beer (around 92%). Antioxidant activity was increased by late dry hopping using ale yeasts for fermenting. Principal component analysis performed with electronic nose data explained up to 97% of the total variability of the compounds in the study. CONCLUSIONS: Combined use of ale and lager yeasts seems to increase the antioxidant capacity and total polyphenol content of beer. Antioxidant activity is increased by late dry hopping. An electronic nose is a suitable device for discriminating the volatile profile complexity in beer. © 2020 Society of Chemical Industry.

Graphene-Doped Tin Oxide Nanofibers and Nanoribbons as Gas Sensors to Detect Biomarkers of Different Diseases through the Breath.

This work presents the development of tin oxide nanofibers (NFs) and nanoribbons (NRs) sensors with graphene as a dopant for the detection of volatile organic compounds (VOCs) corresponding to different chronic diseases (asthma, chronic obstructive pulmonary disease, cystic fibrosis or diabetes). This research aims to determine the ability of these sensors to differentiate between gas samples corresponding to healthy people and patients with a disease. The nanostructures were grown by electrospinning and deposited on silicon substrates with micro-heaters integrated. The morphology of NFs and NRs was characterized by Scanning Electron Microscopy (SEM). A gas line was assembled and programmed to measure a wide range of gases (ethanol, acetone, NO and CO) at different concentrations simulating human breath conditions. Measurements were made in the presence and absence of humidity to evaluate its effect. The sensors were able to differentiate between the concentrations corresponding to a healthy person and a patient with one of the selected diseases. These were sensitive to biomarkers such as acetone and ethanol at low operating temperatures (with responses above 35%). Furthermore, CO and NO response was at high temperatures (above 5%). The sensors had a rapid response, with times of 50 s and recovery periods of about 10 min.