Nanostructured MOS Sensor for the Detection, Follow up, and Threshold Pursuing of Campylobacter Jejuni Development in Milk Samples.

Food poisoning is still the first cause of hospitalization worldwide and the most common microbial agent, Campylobacter jejuni, is the most commonly reported gastrointestinal disease in humans in the EU (European Union) as is reported by the European Union One Health 2018 Zoonoses Report styled by the EFSA (European Food Safety Authority) and ECDC (European Center for Disease Prevention and Control). One of the vehicles of transmission of this disease is milk. Nanostructured MOS (Metal Oxide Semiconductor) sensors have extensively demonstrated their ability to reveal the presence and follow the development of microbial species. The main objective of this work was to find a set up for the detection and development follow up of C. jejuni in milk samples. The work was structured in two different studies, the first one was a feasibility survey and the second one was to follow up the development of the bacteria inside milk samples. The obtained results of the first study demonstrate the ability of the sensor array to differentiate the contaminated samples from the control ones. Thanks to the second study, it has been possible to find the limit of microbial safety of the contaminated milk samples.

Self-Test Procedures for Gas Sensors Embedded in Microreactor Systems.

Metal oxide (MOX) gas sensors sensitively respond to a wide variety of combustible, explosive and poisonous gases. However, due to the lack of a built-in self-test capability, MOX gas sensors have not yet been able to penetrate safety-critical applications. In the present work we report on gas sensing experiments performed on MOX gas sensors embedded in ceramic micro-reaction chambers. With the help of an external micro-pump, such systems can be operated in a periodic manner alternating between flow and no-flow conditions, thus allowing repetitive measurements of the sensor resistances under clean air, R 0 , and under gas exposure, R g a s , to be obtained, even under field conditions. With these pairs of resistance values, eventual drifts in the sensor baseline resistance can be detected and drift-corrected values of the relative resistance response R e s p = ( R 0 - R g a s ) / R 0 can be determined. Residual poisoning-induced changes in the relative resistance response can be detected by reference to humidity measurements taken with room-temperature-operated capacitive humidity sensors which are insensitive to the poisoning processes operative on heated MOX gas sensors.

Application of a Novel S3 Nanowire Gas Sensor Device in Parallel with GC-MS for the Identification of Rind Percentage of Grated Parmigiano Reggiano.

Parmigiano Reggiano cheese is one of the most appreciated and consumed foods worldwide, especially in Italy, for its high content of nutrients and taste. However, these characteristics make this product subject to counterfeiting in different forms. In this study, a novel method based on an electronic nose has been developed to investigate the potentiality of this tool to distinguish rind percentages in grated Parmigiano Reggiano packages that should be lower than 18%. Different samples, in terms of percentage, seasoning and rind working process, were considered to tackle the problem at 360°. In parallel, GC-MS technique was used to give a name to the compounds that characterize Parmigiano and to relate them to sensors responses. Data analysis consisted of two stages: Multivariate analysis (PLS) and classification made in a hierarchical way with PLS-DA ad ANNs. Results were promising, in terms of correct classification of the samples. The correct classification rate (%) was higher for ANNs than PLS-DA, with correct identification approaching 100 percent.

Metal Oxide Nanowire Preparation and Their Integration into Chemical Sensing Devices at the SENSOR Lab in Brescia.

Metal oxide 1D nanowires are probably the most promising structures to develop cheap stable and selective chemical sensors. The purpose of this contribution is to review almost two-decades of research activity at the Sensor Lab Brescia on their preparation during by vapor solid (n-type In2O3, ZnO), vapor liquid solid (n-type SnO2 and p-type NiO) and thermal evaporation and oxidation (n-type ZnO, WO3 and p-type CuO) methods. For each material we've assessed the chemical sensing performance in relation to the preparation conditions and established a rank in the detection of environmental and industrial pollutants: SnO2 nanowires were effective in DMMP detection, ZnO nanowires in NO2, acetone and ethanol detection, WO3 for ammonia and CuO for ozone.

Synthesis and electrochemical study of a hybrid structure based on PDMS-TEOS and titania nanotubes for biomedical applications.

Metallic implants and devices are widely used in the orthopedic and orthodontic clinical areas. However, several problems regarding their adhesion with the living tissues and inflammatory responses due to the release of metallic ions to the medium have been reported. The modification of the metallic surfaces and the use of biocompatible protective coatings are two approaches to solve such issues. In this study, in order to improve the adhesion properties and to increase the corrosion resistance of metallic Ti substrates we have obtained a hybrid structure based on TiO2 nanotubular arrays and PDMS-TEOS films. TiO2 nanotubes have been prepared with two different diameters by means of electrochemical anodization. PDMS-TEOS films have been prepared by the sol-gel method. The morphological and the elemental analysis of the structures have been investigated by scanning electron microscopy and energy dispersive spectroscopy (EDS). Electrochemical impedance spectroscopy (EIS) and polarization curves have been performed during immersion of the samples in Kokubo's simulated body fluid (SBF) at 37 °C to study the effect of structure layers and tube diameter on the protective properties. The obtained results show that the modification of the surface structure of TiO2 and the application of PDMS-TEOS film is a promising strategy for the development of implant materials.

TiO2 nanotubes: recent advances in synthesis and gas sensing properties.

Synthesis--particularly by electrochemical anodization-, growth mechanism and chemical sensing properties of pure, doped and mixed titania tubular arrays are reviewed. The first part deals on how anodization parameters affect the size, shape and morphology of titania nanotubes. In the second part fabrication of sensing devices based on titania nanotubes is presented, together with their most notable gas sensing performances. Doping largely improves conductivity and enhances gas sensing performances of TiO2 nanotubes.

CuO/ZnO nanocomposite gas sensors developed by a plasma-assisted route.

CuO/ZnO nanocomposites were synthesized on Al(2)O(3) substrates by a hybrid plasma-assisted approach, combining the initial growth of ZnO columnar arrays by plasma-enhanced chemical vapor deposition (PE-CVD) and subsequent radio frequency (RF) sputtering of copper, followed by final annealing in air. Chemical, morphological, and structural analyses revealed the formation of high-purity nanosystems, characterized by a controllable dispersion of CuO particles into ZnO matrices. The high surface-to-volume ratio of the obtained materials, along with intimate CuO/ZnO intermixing, resulted in the efficient detection of various oxidizing and reducing gases (such as O(3), CH(3)CH(2)OH, and H(2)). The obtained data are critically discussed and interrelated with the chemical and physical properties of the nanocomposites.

Fabrication and investigation of gas sensing properties of Nb-doped TiO(2) nanotubular arrays.

Synthesis of Nb-containing titania nanotubular arrays at room temperature by electrochemical anodization is reported. Crystallization of pure and Nb-doped TiO(2) nanotubes was carried out by post-growth annealing at 400°C. The morphology of the tubes obtained was characterized by scanning electron microscopy (SEM). Crystal structure and composition of tubes were investigated by glancing incidence x-ray diffraction (GIXRD) and total reflection x-ray fluorescence (TXRF). For the first time gas sensing characteristics of Nb-doped TiO(2) nanotubes were investigated and compared to those of undoped nanotubes. The functional properties of nanotubular arrays towards CO, H(2), NO(2), ethanol and acetone were tested in a wide range of operating temperature. The introduction of Nb largely improves conductivity and enhances gas sensing performances of TiO(2) nanotubes.

Nanostructured metal oxide gas sensors, a survey of applications carried out at SENSOR lab, Brescia (Italy) in the security and food quality fields.

In this work we report on metal oxide (MOX) based gas sensors, presenting the work done at the SENSOR laboratory of the CNR-IDASC and University of Brescia, Italy since the 80s up to the latest results achieved in recent times. In particular we report the strategies followed at SENSOR during these 30 years to increase the performance of MOX sensors through the development of different preparation techniques, from Rheotaxial Growth Thermal Oxidation (RGTO) to nanowire technology to address sensitivity and stability, and the development of electronic nose systems and pattern recognition techniques to address selectivity. We will show the obtained achievement in the context of selected applications such as safety and security and food quality control.

Bovine Serum Albumin protofibril-like aggregates formation: solo but not simple mechanism.

We report an experimental study on the model protein Bovine Serum Albumin (BSA), with the aim of elucidating the mechanisms by which a fully folded globular protein undergoes different aggregation pathways leading to the formation of amyloid fibrils or amorphous aggregates. We observe thermally induced formation of fibrillar structures at pH far from the protein isoelectric point. The increase of electrostatic repulsion results in protein destabilization and in modifications of inter and intra-molecular interactions leading to the growth of fibril-like aggregates stabilized by inter-molecular-ß sheets. The aggregation kinetics is studied by means of fluorescence techniques, light scattering, Circular Dichroism (CD), infrared spectroscopy (FTIR) and Atomic Force Microscopy (AFM). Changes in protein secondary structures turn out to be the driving mechanism of the observed aggregation and they progress in parallel with the growth of Thioflavin T emission intensity and scattering signal. This concurrent behavior suggests a mutual stabilization of elongated protofibril-like structures and of protein conformational and structural changes, which lead to a more rigid and ordered structures. Our results give new insights on BSA self-assembly process in alkaline conditions clearly providing new pieces of evidences of the interplay of several and interconnected mechanisms occurring on different time and length scales.

Surface-driven porphyrin self-assembly on pre-activated Si substrates.

Self-assembled molecular thin films of melamine-bridged bis-porphyrin dyad, both in free form, P(H2)P(H2), or as Zn(II) metallated complex, P(Zn)P(Zn), were deposited on crystalline Si(100) by soaking or drop-casting techniques. The influence of the adopted preparation methodology, the substrate surface pre-activation procedure and the used solvent (THF or CHCl3) on the morphology and surface coverage of the resulting films was investigated by FE-SEM (Field Emission-Scanning Electron Microscopy) and AFM (Atomic Force Microscopy). The chemical composition and electronic structure of the most promising systems were also addressed by XPS (X-ray Photoelectron Spectroscopy). The results pointed out that an accurate tuning of porphyrin-porphyrin, porphyrin-substrate and porphyrin-solvent molecular interactions allow to tailor the morphogenesis and chemico-physical properties of the final self-assembled films. In addition, preliminary gas sensing tests evidenced the potential of the present porphyrin-based films for the development of new molecular sensing devices.

Direct integration of metal oxide nanowires into an effective gas sensing device.

A simple and large-area scalable methodology has been set up for direct integration of metal oxide nanowire bundles into a functional device for gas sensing. It is based on sequential application of two consolidated techniques, namely high temperature vapour transport and condensation for fabrication of metal oxide nanowires, and wet etching of a sacrificial layer. The alumina substrate patterned with a silicon dioxide sacrificial layer does not influence the growth of nanowires and remains unaltered under the high temperature process. The sacrificial layer is finally removed under hydrofluoric acid, the metal oxide nanowires do not suffer modifications and a clean substrate surface can be obtained for deposition of stable metal contacts. The methodology was proven effective for application in a gas sensor device. Electrical measurements indicate that a slightly rectifying Schottky junction is present at low temperatures (up to T = 150 degrees C) between nanowires and platinum electrodes, which vanishes as the temperature increases and under high voltage (bias voltage above approximately 3 V). The results foresee the possibility of growth and integration of nanowire bundles directly into devices, overcoming the need for expensive and time-consuming nanomanipulation techniques.

Vapor phase synthesis, characterization and gas sensing performances of Co3O4 and Au/Co3O4 nanosystems.

Al2O3-supported Co3O4 nanosystems were grown by a Chemical Vapor Deposition route under O2 + H2O atmospheres at 500 degrees C. Subsequently, the preparation of Au/Co3O4 composites was attained by Radio Frequency-Sputtering of gold onto the previous Co3O4 nanodeposits. Important data on the system structure, morphology and chemical composition were obtained by the combined use of complementary techniques, namely Glancing Incidence X-ray Diffraction, Field Emission-Scanning Electron Microscopy, Atomic Force Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Photoelectron Spectroscopy and Secondary Ion Mass Spectrometry. Finally, the gas sensing properties of the synthesized systems were probed in the detection of ethanol and hydrogen. The obtained results revealed significant responses already at moderate temperatures, which could be further enhanced by Co3O4 functionalization with Au nanoparticles.

An Array of MOX Sensors and ANNs to Assess Grated Parmigiano Reggiano Cheese Packs' Compliance with CFPR Guidelines.

Parmigiano Reggiano cheese is one of the most appreciated Italian foods on account of its high nutrient content and taste. Due to its high cost, these characteristics make this product subject to counterfeiting in different forms. In this study, an approach based on an array of gas sensors has been employed to assess if it was possible to distinguish different samples based on their aroma. Samples were characterized in terms of rind percentage, seasoning, and rind working process. From the responses of the sensors, five features were extracted and the capability of these parameters to recognize target classes was tested with statistical analysis. Hence, the performance of the sensors' array was quantified using artificial neural networks. To simplify the problem, a hierarchical approach has been used: three steps of classification were performed, and in each step one parameter of the grated cheese was identified (firstly, seasoning; secondly, rind working process; finally, rind percentage). The accuracies ranged from 88.24% to 100%.

UV-Enhanced Humidity Sensing of Chitosan-SnO2 Hybrid Nanowires.

The surface of SnO2 nanowires was functionalized by chitosan for the development of room-temperature conductometric humidity sensors. SnO2 nanowires were synthesized by the seed-mediated physical-vapor-deposition (PVD) method. Chitosan layers were deposited on top of the SnO2 nanowires by spin coating. Surface morphology, crystal structure, and optical properties of the synthesized hybrid nanostructure were investigated by scanning electron microscope, grazing incidence X-ray diffraction, and UV-Vis absorption measurements. During electrical conductivity measurements, the hybrid nanostructure showed unusual behavior towards various relative humidity (RH) concentrations (25%, 50%, 75%), under UV-light irradiation, and in dark conditions. The highest sensor responses were recorded towards an RH level of 75%, resulting in 1.1 in the dark and 2.5 in a UV-irradiated chamber. A novel conduction mechanism of hybrid nanowires is discussed in detail by comparing the sensing performances of chitosan film, SnO2 nanowires, and chitosan@SnO2 hybrid nanostructures.

Investigation of Reduced Graphene Oxide and a Nb-Doped TiO2 Nanotube Hybrid Structure To Improve the Gas-Sensing Response and Selectivity.

The precise detection of flammable and explosive gases and vapors remains an important issue because of the increasing demand for renewable energy sources and safety requirements in industrial processes. Metal oxides (TiO2, SnO2, ZnO, etc.) are very attractive materials for the manufacturing of chemical gas sensors. However, their gas selectivity issues and further improvement in the sensing response remain a significant challenge. The incorporation of metal oxides with two-dimensional (2D) graphene oxide (GO) is considered to be a promising approach to obtaining hybrid structures with improved gas-sensing performance. Herein, we report the development of GO and niobium-doped titanium dioxide nanotube (NT) hybrid structures with a tunable selectivity and sensing response against hydrogen gas, achieved by properly controlling the degree of reduction and concentration of GO. The effects of these parameters are systematically studied in terms of the response amplitude and selectivity. It was found that, compared to undoped titanium dioxide nanotubes, the hybrid material with an optimal concentration of reduced-GO and the introduction of niobium shows an increase in hydrogen response of about an order of magnitude and a simultaneous reduction of the response to possible interfering compounds such as carbon monoxide and acetone, thus providing enhanced selectivity. This research may provide an efficient way to enhance the chemical sensing performance of metal oxide nanomaterials.

Nanomaterial Gas Sensors for Online Monitoring System of Fruit Jams.

Jams are appreciated worldwide and have become a growing market, due to the greater attention paid by consumers for healthy food. The selected products for this study represent a segment of the European market that addresses natural products without added sucrose or with a low content of natural sugars. This study aims to identify volatile organic compounds (VOCs) that characterize three flavors of fruit and five recipes using gas chromatography-mass spectrometry (GC-MS) and solid-phase micro-extraction (SPME) analysis. Furthermore, an innovative device, a small sensor system (S3), based on gas sensors with nanomaterials has been used; it may be particularly advantageous in the production line. Results obtained with linear discriminant analysis (LDA) show that S3 can distinguish among the different recipes thanks to the differences in the VOCs that are present in the specimens, as evidenced by the GC-MS analysis. Finally, this study highlights how the thermal processes for obtaining the jam do not alter the natural properties of the fruit.

Effects of aluminium sulphate in the mouse liver: similarities to the aging process.

Aluminium (Al) is a ubiquitous metal that is potentially toxic to the brain. Its effects on other fundamental organs are not completely understood. This morphological in vivo study sought to compare sublethal hepatotoxic changes and Al deposition in adult mice that orally ingested Al sulphate daily for 10 months, in age matched control mice that drank tap water and in senescent mice (24 months old). Livers were examined for collagen deposition using Sirius red and Masson, for iron accumulation using Perls' stain. Light, electron microscopy and morphometry were used to assess fibrosis and vascular changes. Scanning transmission electron microscopy and EDX microanalysis were used to detect in situ elemental Al. Iron deposition, transferrin receptor expression were significantly altered following Al exposure and in the aged liver but were unaffected in age matched control mice. In Al treated mice as in senescent mice, endothelial thickness was increased and porosity was decreased like perisinusoidal actin. Furthermore, Al stimulated the deposition of collagen and laminin, mainly in acinar zones 1 and 3. Pseudocapillarization and periportal laminin in senescent mice were similar to Al treated adult liver. In conclusion, prolonged Al sulphate intake accelerates features of senescence in the adult mice liver.

Gas sensing properties of columnar CeO2 nanostructures prepared by chemical vapor deposition.

Columnar CeO2 nanostructures are grown on alumina substrates by a template- and catalyst-free Chemical Vapor Deposition (CVD) approach and subsequently tested as resistive gas sensors of CH3COCH3, H2, NO2. The sensor response is stable and reproducible throughout the whole working temperature range (200-500 degrees C) and directly dependent on the analyte gas and the adopted operating conditions. The higher sensitivity with respect to that displayed by continuous CeO2 thin films demonstrates the potential of fabricating nanostructured sensing devices characterized by improved functional performances.

Sensitivity-Selectivity Trade-Offs in Surface Ionization Gas Detection.

Surface ionization (SI) provides a simple, sensitive, and selective method for the detection of high-proton affinity substances, such as organic decay products, medical and illicit drugs as well as a range of other hazardous materials. Tests on different kinds of SI sensors showed that the sensitivity and selectivity of such devices is not only dependent on the stoichiometry and nanomorphology of the emitter materials, but also on the shape of the electrode configurations that are used to read out the SI signals. Whereas, in parallel-plate capacitor devices, different kinds of emitter materials exhibit a high level of amine-selectivity, MEMS (micro-electro-mechanical-systems) and NEMS (nanowire) versions of SI sensors employing the same kinds of emitter materials provide significantly higher sensitivity, however, at the expense of a reduced chemical selectivity. In this paper, it is argued that such sensitivity-selectivity trade-offs arise from unselective physical ionization phenomena that occur in the high-field regions immediately adjacent to the surfaces of sharply curved MEMS (NEMS) emitter and collector electrodes.