Room Temperature Ammonia Gas Sensor Based on p-Type-like V2O5 Nanosheets towards Food Spoilage Monitoring

Gas sensors play an important role in many areas of human life, including the monitoring of production processes, occupational safety, food quality assessment, and air pollution monitoring. Therefore, the need for gas sensors to monitor hazardous gases, such as ammonia, at low operating temperatures has become increasingly important in many fields. Sensitivity, selectivity, low cost, and ease of production are crucial characteristics for creating a capillary network of sensors for the protection of the environment and human health. However, developing gas sensors that are not only efficient but also small and inexpensive and therefore integrable into everyday life is a difficult challenge. In this paper, we report on a resistive sensor for ammonia detection based on thin V₂O₅ nanosheets operating at room temperature. The small thickness and porosity of the V₂O₅ nanosheets give the sensors good performance for sensing ammonia at room temperature (RT), with a relative change of resistance of 9.4% to 5 ppm ammonia (NH₃) and an estimated detection limit of 0.4 ppm. The sensor is selective with respect to the seven interferents tested; it is repeatable and stable over the long term (four months). Although V₂O₅ is generally an n-type semiconductor, in this case the nanosheets show a p-type semiconductor behavior, and thus a possible sensing mechanism is proposed. The device's performance, along with its size, low cost, and low power consumption, makes it a good candidate for monitoring freshness and spoilage along the food supply chain.

Mn3O4@ZnO Hybrid Material: An Excellent Photocatalyst for the Degradation of Synthetic Dyes including Methylene Blue, Methyl Orange and Malachite Green

In this study, we synthesized hybrid systems based on manganese oxide@zinc oxide (Mn₃O₄@ZnO), using sol gel and hydrothermal methods. The hybrid materials exhibited hierarchical morphologies and structures characterized by the hexagonal phase of ZnO and the tetragonal phase of Mn₃O₄. The hybrid materials were tested for degradation of methylene blue (MB), methyl orange (MO), and malachite green (MG) under ultraviolet (UV) light illumination. The aim of this work was to observe the effect of various amounts of Mn₃O₄ in enhancing the photocatalytic properties of ZnO-based hybrid structures towards the degradation of MB, MO and MG. The ZnO photocatalyst showed better performance with an increasing amount of Mn₃O₄, and the degradation efficiency for the hybrid material containing the maximum amount of Mn₃O₄ was found to be 94.59%, 89.99%, and 97.40% for MB, MO and MG, respectively. The improvement in the performance of hybrid materials can be attributed to the high charge separation rate of electron-hole pairs, the co-catalytic role, the large number of catalytic sites, and the synergy for the production of high quantities of oxidizing radicals. The performance obtained from the various Mn₃O₄@ZnO hybrid materials suggest that Mn₃O₄ can be considered an effective co-catalyst for a wide range of photocatalytic materials such as titanium dioxide, tin oxide, and carbon-based materials, in developing practical hybrid photocatalysts for the degradation of dyes and for wastewater treatment.

Nanosensor Based on Thermal Gradient and Machine Learning for the Detection of Methanol Adulteration in Alcoholic Beverages and Methanol Poisoning

Methanol, naturally present in small quantities in the distillation of alcoholic beverages, can lead to serious health problems. When it exceeds a certain concentration, it causes blindness, organ failure, and even death if not recognized in time. Analytical techniques such as chromatography are used to detect dangerous concentrations of methanol, which are very accurate but also expensive, cumbersome, and time-consuming. Therefore, a gas sensor that is inexpensive and portable and capable of distinguishing methanol from ethanol would be very useful. Here, we present a resistive gas sensor, based on tin oxide nanowires, that works in a thermal gradient. By combining responses at various temperatures and using machine learning algorithms (PCA, SVM, LDA), the device can distinguish methanol from ethanol in a wide range of concentrations (1–100 ppm) in both dry air and under different humidity conditions (25–75% RH). The proposed sensor, which is small and inexpensive, demonstrates the ability to distinguish methanol from ethanol at different concentrations and could be developed both to detect the adulteration of alcoholic beverages and to quickly recognize methanol poisoning.

Exploring volatile organic compound emission from thermally modified wood by PTR-ToF-MS

Thermal modification of wood is a well-known industrial process performed to increase durability and dimensional stability or to change the colour of the natural wood. The treatment influences many other...

Facile synthesis of a luminescent carbon material from yogurt for the efficient photocatalytic degradation of methylene blue

The present study is focused on yogurt as a simple, inexpensive, abundant, and green source for the preparation of luminescent carbon material for enhancing the photodegradation of methylene blue (MB). It introduces an ecological and sustainable approach for the large-scale production of carbon material using the direct thermal annealing of yogurt in a muffle furnace. The size of the as-prepared carbon material is about 200–300 nm, with average particle size distribution of 355 nm. The material exhibits clear luminescence under illumination with ultraviolet light. The synthesized carbon material shows an outstanding degradation functionality of MB under the irradiation of ultraviolet (UV) light in aqueous media. Various dye degradation parameters such as initial dye concentration, catalyst dose, pH of dye solution, and scavenger effects have been investigated. The optimum MB concentration was found to be 2.3 × 10⁻⁵ M with a degradation efficiency of 94.8%. The degradation was highly enhanced at pH 11 with a degradation efficiency of 98.11%. The degradation of MB under highly alkaline conditions was mainly governed by the high amount of hydroxyl radicals. Furthermore, the scavenger study confirmed that the hydroxyl radicals were mainly involved in the degradation process. The degradation kinetics of MB followed first order kinetics with large values of rate constant. The reusability was also studied to ensure the stability of the as-prepared carbon material during the degradation of MB. The preparation of carbon materials with efficient photosensitivity for the degradation of organic dyes from yogurt shows a green and innovative methodology. Therefore, it can be of great interest for future studies related to energy and environmental applications.

Left hand side: structural and optical aspects of the as-prepared carbon material from yogurt. Right hand side: the absorbance spectra of methylene blue degradation using the as-prepared carbon material from yogurt.

Sensing Performance of Thermal Electronic Noses: A Comparison between ZnO and SnO2 Nanowires

In recent times, an increasing number of applications in different fields need gas sensors that are miniaturized but also capable of distinguishing different gases and volatiles. Thermal electronic noses are new devices that meet this need, but their performance is still under study. In this work, we compare the performance of two thermal electronic noses based on SnO2 and ZnO nanowires. Using five different target gases (acetone, ammonia, ethanol, hydrogen and nitrogen dioxide), we investigated the ability of the systems to distinguish individual gases and estimate their concentration. SnO2 nanowires proved to be more suitable for this purpose with a detection limit of 32 parts per billion, an always correct classification (100%) and a mean absolute error of 7 parts per million.

Quantitative Assessment of Trout Fish Spoilage with a Single Nanowire Gas Sensor in a Thermal Gradient

The response of a single tin oxide nanowire was collected at different temperatures to create a virtual array of sensors working as a nano-electronic nose. The single nanowire, acting as a chemiresistor, was first tested with pure ammonia and then used to determine the freshness status of trout fish (Oncorhynchus mykiss) in a rapid and non-invasive way. The gas sensor reacts to total volatile basic nitrogen, detecting the freshness status of the fish samples in less than 30 s. The sensor response at different temperatures correlates well with the total viable count (TVC), demonstrating that it is a good (albeit indirect) way of measuring the bacterial population in the sample. The nano-electronic nose is not only able to classify the samples according to their degree of freshness but also to quantitatively estimate the concentration of microorganisms present. The system was tested with samples stored at different temperatures and classified them perfectly (100%), estimating their log(TVC) with an error lower than 5%.

Recent Advances of Silver Nanoparticles in Cancer Diagnosis and Treatment

Background:

Silver nanoparticles (AgNPs) are well-known as a promising antimicrobial material; they have been widely used in many commercial products against pathogenic agents. Despite a growing concern regarding the cytotoxicity, AgNPs still have attracted considerable interest worldwide to develop a new generation of diagnostic tool and effective treatment solution for cancer cells.

Objective:

This paper aims to review the advances of AgNPs applied for cancer diagnosis and treatment.

Methods:

The database has been collected, screened and analysed through up-to-date scientific articles published from 2007 to May 2019 in peer-reviewed international journals.

Results:

The findings of the database have been analysed and divided into three parts of the text that deal with AgNPs in cancer diagnosis, their cytotoxicity, and the role as carrier systems for cancer treatment. Thanks to their optical properties, high conductivity and small size, AgNPs have been demonstrated to play an essential role in enhancing signals and sensitivity in various biosensing platforms. Furthermore, AgNPs also can be used directly or developed as a drug delivery system for cancer treatment.

Conclusion:

The review paper will help readers understand more clearly and systematically the role and advances of AgNPs in cancer diagnosis and treatment.

Multi gas sensors using one nanomaterial, temperature gradient, and machine learning algorithms for discrimination of gases and their concentration

In this work, four identical micro sensors on the same chip with noble metal decorated tin oxide nanowires as gas sensing material were located at different distances from an integrated heater to work at different temperatures. Their responses are combined in highly informative 4D points that can qualitatively (gas recognition) and quantitatively (concentration estimate) discriminate all the tested gases. Two identical chips were fabricated with tin oxide (SnO₂) nanowires decorated with different metal nanoparticles: one decorated with Ag nanoparticles and one with Pt nanoparticles. Support Vector Machine was used as the "brain" of the sensing system. The results show that the systems using these multisensor chips were capable of achieving perfect classification (100%) and good estimation of the concentration of tested gases (errors in the range 8-28%). The Ag decorated sensors did not have a preferential gas, while Pt decorated sensors showed a lower error towards acetone, hydrogen and ammonia. Combination of the two sensor chips improved the overall estimation of gas concentrations, but the individual sensor chips were better for some specific target gases.

ZnO nanowires-C microfiber hybrid nanosensor for liquefied petroleum gas detection

Zinc oxide nanowires are integrated onto carbon microfibers using a two-step approach which includes electrochemical deposition of zinc and its thermal oxidation. Such nano-on-micro hybrid architecture is then used as resistive gas sensor. Some properties like mechanical flexibility, low cost and large-area fabrication make this design appealing for different applications. The huge surface-to-volume ratio of such structure comes from being structured at both microscale and nanoscale (ZnO nanowires and C microfiber) and leads to a strong and rapid response/recovery times when it is used as a gas sensor. The fabrication process of the ZnO-microC device is very simple and doesn't involve any expensive lithographic step. The sensors show excellent liquefied petroleum gas sensing properties, with very fast response on gas exposure (about 3 s) and very good reversibility (less than 2%). In addition, the carbon microfiber substrate allows the use of the ZnO-microC sensor also in applications where flexibility is required (for example integrated in fabric).