Barbara Fabbri

Metal Sulfides as Sensing Materials for Chemoresistive Gas Sensors

This work aims at a broad overview of the results obtained with metal-sulfide materials in the field of chemoresistive gas sensing. Indeed, despite the well-known electrical, optical, structural and morphological features previously described in the literature, metal sulfides present lack of investigation for gas sensing applications, a field in which the metal oxides still maintain a leading role owing to their high sensitivity, low cost, small dimensions and simple integration, in spite of the wide assortment of sensing materials. However, despite their great advantages, metal oxides have shown significant drawbacks, which have led to the search for new materials for gas sensing devices. In this work, Cadmium Sulfide and Tin (IV) Sulfide were investigated as functional materials for thick-film chemoresistive gas-sensors fabrication and they were tested both in thermo- and in photo-activation modes. Furthermore, electrical characterization was carried out in order to verify their gas sensing properties and material stability, by comparing the results obtained with metal sulfides to those obtained by using their metal-oxides counterparts. The results highlighted the possibility to use metal sulfides as a novel class of sensing materials, owing to their selectivity to specific compounds, stability, and the possibility to operate at room temperature.

Resonant photoactivation of cadmium sulfide and its effect on the surface chemical activity

Photo-enhanced surface chemical activity of cadmium sulfide gives rise to a wide class of surface-dependent phenomena, such as heterogeneous photocatalysis, chemoresistivity, and chemiluminescence, which have several technological and scientific applications. In this work, the photochemical properties of nanostructured cadmium sulfide films are investigated by means of electrical conductance measurements in controlled atmosphere, while irradiated by light of wavelengths ranging from 400 to 645 nm. Chemisorption of benzene, carbon monoxide, methane, ethanol, and hydrogen sulfide onto CdS surface has been analyzed as a function of the wavelength, in a gas concentration range of the order of parts per million. It resulted that the increase of photoconductance with gas adsorption is resonant with the bandgap energy. It turns out that this resonant enhancement of the surface chemical activity can be of advantage for all the optical and chemical mechanisms that depend upon it. An interpretation of these results...

Chemoresistive gas sensors for the detection of colorectal cancer biomarkers.

Numerous medical studies show that tumor growth is accompanied by protein changes that may lead to the peroxidation of the cell membrane with consequent emission of volatile organic compounds (VOCs) by breath or intestinal gases that should be seen as biomarkers for colorectal cancer (CRC). The analysis of VOCs represents a non-invasive and potentially inexpensive preliminary screening technique. An array of chemoresistive gas sensors based on screen-printed metal oxide semiconducting films has been selected to discriminate gases of oncological interest, e.g., 1-iodononane and benzene, widely assumed to be biomarkers of colorectal cancer, from those of interference in the gut, such as methane and nitric oxide.

Modelling Soil Water Content in a Tomato Field: Proximal Gamma Ray Spectroscopy and Soil–Crop System Models

Proximal soil sensors are taking hold in the understanding of soil hydrogeological processes involved in precision agriculture. In this context, permanently installed gamma ray spectroscopy stations represent one of the best space–time trade off methods at field scale. This study proved the feasibility and reliability of soil water content monitoring through a seven-month continuous acquisition of terrestrial gamma radiation in a tomato test field. By employing a 1 L sodium iodide detector placed at a height of 2.25 m, we investigated the gamma signal coming from an area having a ~25 m radius and from a depth of approximately 30 cm. Experimental values, inferred after a calibration measurement and corrected for the presence of biomass, were corroborated with gravimetric data acquired under different soil moisture conditions, giving an average absolute discrepancy of about 2%. A quantitative comparison was carried out with data simulated by AquaCrop, CRITeRIA, and IRRINET soil–crop system models. The different goodness of fit obtained in bare soil condition and during the vegetated period highlighted that CRITeRIA showed the best agreement with the experimental data over the entire data-taking period while, in presence of the tomato crop, IRRINET provided the best results.

Crystalline Microporous Organosilicates with Reversed Functionalities of Organic and Inorganic Components for Room-Temperature Gas Sensing

A deepened investigation on an innovative organic-inorganic hybrid material, referred to as ECS-14 (where ECS = Eni carbon silicates), revealed the possibility to use them as gas sensors. Indeed, among ECS phases, the crystalline state and the hexagonal microplateletlike morphology characteristic of ECS-14 seemed favorable properties to obtain continuous and uniform films. ECS-14 phase was used as functional material in screen-printable compositions and was thus deposited by drop coating for morphological, structural, thermal, and electrical characterizations. Possible operation at room temperature was investigated as technological progress, offering intrinsic safety in sensors working in harsh or industrial environments and avoiding high power consumption of most common sensors based on metal oxide semiconductors. Electrical characterization of the sensors based on ECS-14 versus concentrations of gaseous analytes gave significant results at room temperature in the presence of humidity, thereby demonstrating fundamental properties for a good quality sensor (speed, reversibility, and selectivity) that make them competitive with respect to systems currently in use. Remarkably, we observed functionality reversal of the organic and inorganic components; that is, in contrast to other hybrids, for ECS-14 the functional site has been ascribed to the inorganic phase while the organic component provided structural stability to the material. The sensing mechanism for humidity was also investigated.

Tin (IV) Sulfide chemoresistivity: A possible new gas sensing material

In the last years, the research in the gas sensor field had a significant upward thrust. Regarding the chemoresistive gas sensors, this has produced a remarkable study of metal oxides semiconductors which, however, have shown different limits. In particular their low selectivity and lack of stability take them to an unreliable responses over time. For this reason, in this work it was decided to study the chemoresistive behavior of a non metal oxide semiconductor as Tin (IV) Sulfide (SnS2). SnS2 nanoparticles was synthetized by precipitation reaction in aqueous solution. Then, structural chemical and morphological characterizations were carried out by means of X-Ray Diffraction and SEM techniques. Furthermore, the thermal stability of the powder was studied with thermogravimetric analysis. The sensitive films were obtained by preparing a screen-printing paste and then depositing it on alumina substrates by means of screen-printing technique. The sensing properties of the obtained devices were tested with several gases at different working temperatures. At the best working temperature, a high selectivity to ketones and aldehydes, with respect to different types of molecules, was observed.

Detection of Tumor Markers and Cell Metabolites in Cell Cultures, Using Nanostructured Chemoresistive Sensors

Nowadays, tumor markers detection is one of the most dynamic field of research for medical technologies, as it seems a reliable source of screening technologies able to both detect neoplasms before their degeneration into malignant forms, and monitor possible relapses after the main cancer removal. On the other hand, studying neoplastic cell cultures behaviour, and their vitality in real time, places problems given to the high proliferation rate of the tumor cells. In this work, nanostructured chemoresistive sensors, sensing unit able to detect volatile chemicals in concentrations up to part per billions, have been used to detect neoplastic markers, with the idea to develop a technology able to follow in real time cell cultures and neoplasms growth, for both research and application in the medical field.

Eni Carbon Silicates: Innovative Hybrid Materials for Room-Temperature Gas Sensing

The purpose of this work was to satisfy both materials and technological sciences, on the one hand implementing innovative hybrid materials referred to as ECS (Eni Carbon Silicate) in gas sensors manufacturing, and on the other hand verifying their possible operation at room temperature as a technological progress. The ECS-14 and ECS-13 phases were employed as functional materials for films deposited by drop coating onto alumina substrates. Room-temperature gas tests were performed to study their potential sensing properties. In humidity conditions, the ECS-14 based sensor showed outstanding performance and a complete calibration vs. moisture concentration was obtained.

On the Optimization of a MEMS Device for Chemoresistive Gas Sensors

In recent years, research in the gas sensor field has experienced a significant boost [1]. [...]

Sustainable Water Management: Sensors for Precision Farming

The application of Site Specific Crop Management (SSCM) consists of the knowledge of the variability of soil and yield. [...]