New insight in biomedical measurements

L'abstract è presente nell'allegato / the abstract is in the attachmen

Employment of Nb2O5 thin-films for ethanol sensing

Gas sensors attract the attention of research since years because of their good performance and the extremely wide field of application. Environmental monitoring, chemical and industrial processes, automotive, medical diagnosis and healthcare are few of such applications. Chemical gas sensors are able to detect specific gases in a wide range of concentration going from few ppb to hundreds ppm. This paper deals with such a topic and presents a novel gas sensor for ethanol based on a Nb 2 O 5 thin sensing film. The sensor was realized by depositing the niobium oxide layer on a tiny alumina substrate by means of a lab-scale plasma sputtering reactor. Subsequently, the sensor was characterized and it revealed good sensing performance towards ethanol. Ethanol monitoring finds application in several fields including breath analyzers for assessing drunk-driving situations, industrial monitoring, medical diagnosis and environmental safety. The proposed sensor, thanks to its good sensitivity, selectivity, wide concentration range, low-cost and low power consumption, can be a suitable solution in such applications

Development and characterization of sensors for human health

L'abstract è presente nell'allegato / the abstract is in the attachmen

Hydrogen chemoresistive sensor for the analysis of gut health

Hydrogen is a target gas in the assessment of gut health. Several are the approaches to estimate the concentration of this gas, endogenously present in the gut and, of course, in the blood and the exhaled breath. In this paper, development and characterization of a resistive gas sensor for hydrogen monitoring is reported. The sensing material is based on Nb2O5 Pt thin films, obtained by depositing a niobium oxide layer and a platinum one on a tiny alumina substrate, by means of a lab-scale plasma sputtering reactor. The deposited layers were treated with a thermal process at 600 °C for 30 min. The developed devices were characterized in a hydrogen concentration range of 2000 ppm to 80000 ppm, showing promising results

Ethanol breath measuring system

Driving after drinking is considered extremely dangerous and severe limits to alcohol drink before driving are enforced in several countries. This paper describes a simple and cheap device which is capable of estimating the blood ethanol level from the expired breath. The device employs a 3 mm×6 mm gas sensor based on Nb 2 O 5 thin-film which features good sensing performance towards ethanol. A suitable electronic circuit is employed in order to measure the conductivity of the gas sensor and to control its working temperature. The circuit is based on a small microcontroller board (Teensy 3.2) and some additional analog circuitry. Similar devices are already available off-theshelf, however, most of them do not guarantee an accuracy suitable for a quantitative measurement of breath ethanol. The proposed system, instead, has been developed trying to optimize accuracy, power consumption and size. Furthermore, such a system employs a novel gas sensor based on a Nb 2 O 5 sensing film, which has not yet been employed in such a field. The system allows one to set the working temperature of the sensor at its optimal value (350 °C) and to simultaneously measure the sensor resistance in the range between 10 MΩ and approximately 1 GΩ. The quite low power consumption together with the very small size of the system make it very suitable for portable applications such as alcohol drive tests which can warn drivers before starting driving

Recent Advancements in TiO2 Nanostructures: Sustainable Synthesis and Gas Sensing

The search for sustainable technology-driven advancements in material synthesis is a new norm, which ensures a low impact on the environment, production cost, and workers' health. In this context, non-toxic, non-hazardous, and low-cost materials and their synthesis methods are integrated to compete with existing physical and chemical methods. From this perspective, titanium oxide (TiO2) is one of the fascinating materials because of its non-toxicity, biocompatibility, and potential of growing by sustainable methods. Accordingly, TiO2 is extensively used in gas-sensing devices. Yet, many TiO2 nanostructures are still synthesized with a lack of mindfulness of environmental impact and sustainable methods, which results in a serious burden on practical commercialization. This review provides a general outline of the advantages and disadvantages of conventional and sustainable methods of TiO2 preparation. Additionally, a detailed discussion on sustainable growth methods for green synthesis is included. Furthermore, gas-sensing applications and approaches to improve the key functionality of sensors, including response time, recovery time, repeatability, and stability, are discussed in detail in the latter parts of the review. At the end, a concluding discussion is included to provide guidelines for the selection of sustainable synthesis methods and techniques to improve the gas-sensing properties of TiO2

Nanofibers and nanoporous metal oxides for gas sensing applications

Air pollution is one of the greatest problems that the world facing is facing today. The World Health Organization (WHO) has provided air quality guidelines, which represent the most widely agreed and up-to-date assessments of air pollutants on human health, recommending stringent thresholds for air quality. This consequently signifies the need to develop gas sensors with the specifications that meet WHO targets. Additionally, gas sensors are also used in variety of other applications such as in many industrial surveillance and processes, automotive, aviation and food industries, medical analysis and diagnostics as well as homeland security and defense. It has been demonstrated that the key factors for developing efficient semiconducting gas sensors is to make use of selected metal oxides after engineering their morphologies and crystallographies. It is well-known that nanostructured metal oxides are generally superior in performance due to their high specific surface area. Hence, searching for the right nanostructured metal oxides with high specific surface area and controllable structures for effective gas sensing is an important research goal nowadays. Many studies, however, have focused on creating nanofibers and nanopores as these morphologies are recognized to be amongst the most efficient for gas sensing applications. Due to the aforementioned justifications, the author of this PhD thesis became involved in the investigation of three different metal oxide nanofibers and nanopores metal oxides, which are tin oxide (SnO2) nanofibers, niobium oxide (Nb2O5) and tungsten trioxide (WO3) nanopores in both nanoporous and nanofibrious structures. There are many different types of gas sensors including those based on conductometric, Schottky and optical templates. In this research, the PhD candidate explored these three templates and investigated their performances when nanofibers and nanopores SnO2, Nb2O5 and WO3 sensitive layers are incorporated with them. To develop the nanostructured sensing films, the author chose electrospinning and anodization synthesis methods which are the most compatible for forming nanofibrious and nanoporous structures. In the first stage, the PhD candidate demonstrated hydrogen (H2) gas sensors based on hollow and filled well-aligned electrospun SnO2 nanofibers, operating at a low temperature of 150 °C.In the second stage of this research, the PhD candidate developed nanoporous Nb2O5 Schottky diode based ethanol (C2H5OH), H2 and methane (CH4) sensors. The sensing behaviours were studied in terms of the Schottky barrier height variations and properties of the metal catalysts. In the third stage, the PhD candidate focused on developing nanoporous Nb2O5 optical based H2 sensors. The compact nanoporous networks with high active surface areas demonstrated excellent absorbance changes at 100 °C with the response factor of 12.1 %. In the last stage, the PhD candidate explored Schottky diode based C2H5OH and H2 gas sensors fabricated via anodization of tungsten (W) foil to form nanoporous WO3 films. In summary, the PhD candidate believes that the studies carried out in the process of this research provided an in-depth vision regarding the fabrication and performance of nanofibers and nanoporous metal oxide based gas sensors

Artificial olfactory system for multi-component analysis of gas mixtures.

Gas analysis is an important part of our world and gas sensing technology is becoming more essential for various aspects of our life. A novel approach for gas mixture analysis by using portable gas chromatography in combination with an array of highly integrated and selective metal oxide (MOX) sensors has been studied. We developed a system with small size (7 x 13 x 16 inches), low power consumption (~10 W) and absence of special carrier gases designed for portable field analysis (assuming apriori calibration). Low ppb and even sub-ppb level of detection for some VOCs was achieved during the analysis of 50 ml of gas samples. A detailed description of our innovative design of multi-sensory platforms based on MOX sensors for multidimensional portable gas chromatography is provided in detail in this work. As a part of this effort, we successfully synthesized nanocomposite gas sensors based on SnO2 for selective detection of hydrogen sulfide, mercaptans, alcohols, ketones and heavy hydrocarbons. The morphology of the prepared sensors was closely studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), transition electron microscopy (TEM) and X-Ray diffraction (XRD). Optical and electrical properties of polycrystalline SnO2 were investigated by using UV-Vis spectroscopy, transmission line measurement (TLM) and four probe resistance measurement techniques. Furthermore, more advanced gas sensing performance for detection of benzene, toluene, ethylbenzene, and O-xylene (BTEX) of polycrystalline SnO2 film (30 nm) coated with bimetal Au:Pd (9:1 molar ratio) nanoclusters was measured. Finally, besides the experimental result, the theoretical validation of the detector’s performance was provided based on high catalytic activity of nanocomposite materials and its superior electronic structure for gas detection compared to the polycrystalline SnO2. The theoretical background of gas chemisorption process at the surface of polycrystalline SnO2 was reviewed in this work. Furthermore, one dimensional Poisson equation relates surface energy states ( and ) and the bulk electronic structure ( and ) of polycrystalline SnO2. The main theory of electronic processes on the surface of semiconductors during the gas chemisorption was further applied in a case of nanocomposite materials

Metal oxide semiconductors as humidity and NOx sensors for environmental monitoring

Semiconducting metal oxide (SMO) sensors are one of the most widely studied groups of chemiresistive gas sensors due to their unique advantages such as low cost, small size, measurement simplicity, durability, ease of fabrication, and low detection limits (< ppm levels). Moreover, most SMO based sensors tend to be long-lived and somewhat resistant to poisoning. The SMO undergoes reduction or oxidation while reacting with the target gas and this process causes an exchange of electrons at a certain characteristic rate, thereby affecting the sensor’s resistance and yielding a certain signal. The aim of this PhD is to fabricate new semiconducting metal oxide sensors capable of detecting humidity and/or NOx gas. The research is subdivided into three main different parts: - The first is to prepare SMO sensors within a template (inorganic clay e.g. Sepiolite, glass): a) ZnO has been synthesized into the sepiolite structure by means of different acid treatments in order to check the sensitivity of the resulting materials toward humidity and NO2. Different samples have been prepared S1, S2, S6 and S24 for the samples acidified for 1, 2, 6 and 24 hours, respectively. Sepiolite leached for 2 h (S2) showed a significant ability to detect quite low Relative Humidity (RH) values. Also, S2 revealed a significant capability for detecting NO2 and H2 in an optimal working temperature 300°C. b) Crystallization of zinc oxide by melt quenching technique; The idea is to check the possibility to fabricate a percolated network from ZnO crystals within a glass matrix by means of crystallization process then to test the resulting material as NOx gas sensor. A melt with nominal composition 58% ZnO 33.3% B2O3 4% WO3 4% Bi2O3 has been quenched. The chosen glass sample was then subjected to the heat treatment for 15 hours at the temperature close to the established Tx (crystallization temperature). As obtained glass ceramic material with adding a ZnO sol-gel (to improve the adhesion of the ink onto alumina substrate) gives a great ability to detect NO2 at a quite low working temperature (150ºC), in conditions close to the environmental one's. This is a promising approach for glass ceramic materials in sensors application which could be used not only as humidity sensors but also for detecting other several gases with a quite good selectivity. - The second part is Li – doped iron oxide as a new material for NO2 detection: Various compositions of lithium doped hematite containing 1, 2, 5, 10, 15, and 20 atomic percent ‎were synthesized by solid state reaction. Electrochemical impedance spectroscopy ‎‎ (EIS) analyses under air and argon were used to determine the semiconducting behavior of the ‎samples (n- or p-type) and to ‎investigate the sensitivity of these materials towards NO2. Lithium doped hematite samples exhibit an n type semiconducting behavior. Lithium ferrites could work as NO2 sensors at a quite low operating temperature (200°C). Generally, sensor response of lithium ferrites towards NO2 revealed an acceptable linear evolution with gas concentration for some compositions. - The third is commercial SMO; In2O3 and ZnO with different morphologies. The objective of this work is the development of materials with hierarchical architectures for the realization of gas sensors capable of detecting low concentration of NO2 in air at low temperature. Different films have been prepared: ZnO and In2O3 thick films, ZnO thin films prepared by sol-gel technique, ZnO nanorods (NR) prepared by technology template of ZnO films obtained by Sol gel and ZnO nanowires (NW) prepared by electrospinning. ZnO thick film and ZnO thin film have the best sensitivity towards NO2 among the other samples