M. L. Miglietta

Wireless Sensor Networks for Distributed Chemical Sensing: Addressing Power Consumption Limits With On-Board Intelligence

Chemicals detection and quantification is extremely important for ensuring safety and security in multiple application domains like smart environments, building automation, etc. Characteristics of chemical signal propagation make single point of measure approach mostly inefficient. Distributed chemical sensing with wireless platforms may be the key for reconstructing chemical images of sensed environment but its development is currently hampered by technological limits on solid-state sensors power management. We present the implementation of power saving sensor censoring strategies on a novel wireless electronic nose platform specifically designed for cooperative chemical sensing and based on TinyOS. An on-board sensor fusion component complements its software architecture with the capability of locally estimate air quality and chemicals concentrations. Each node is hence capable to decide the informative content of sampled data extending the operative lifespan of the entire network. Actual power savings are modeled and estimated with a measurement approach in experimental scenarios.

Genotoxic and cytotoxic effects of ZnO nanoparticles for Dunaliella tertiolecta and comparison with SiO2 and TiO2 effects at population growth inhibition levels

The increasing use of oxide nanoparticles (NPs) in commercial products has intensified the potential release into the aquatic environment where algae represent the basis of the trophic chain. NP effects upon algae population growth were indeed already reported in literature, but the concurrent effects at cellular and genomic levels are still largely unexplored. Our work investigates the genotoxic (by COMET assay) and cytotoxic effects (by qualitative ROS production and cell viability) of ZnO nanoparticles toward marine microalgae Dunaliella tertiolecta. A comparison at defined population growth inhibition levels (i.e. 50% Effect Concentration, EC50, and No Observed Effect Concentration, NOEC) with SiO2 and TiO2 genotoxic effects and previously investigated cytotoxic effects (Manzo et al., 2015) was performed in order to elucidate the possible diverse mechanisms leading to algae growth inhibition. After 72h exposure, ZnO particles act firstly at the level of cell division inhibition (EC50: 2mg Zn/L) while the genotoxic action is evident only starting from 5mg Zn/L. This outcome could be ascribable mainly to the release of toxic ions from the aggregate of ZnO particle in the proximity of cell membrane. In the main, at EC50 and NOEC values for ZnO NPs showed the lowest cytotoxic and genotoxic effect with respect to TiO2 and SiO2. Based on Mutagenic Index (MI) the rank of toxicity is actually: TiO2>SiO2>ZnO with TiO2 and SiO2 that showed similar MI values at both NOEC and EC50 concentrations. The results presented herein suggest that up to TiO2 NOEC (7.5mg/L), the algae DNA repair mechanism is efficient and the DNA damage does not result in an evident algae population growth inhibition. A similar trend for SiO2, although at lower effect level with respect to TiO2, is observable. The comparison among all the tested nanomaterial toxicity patterns highlighted that the algae population growth inhibition occurred through pathways specific for each NP also related to their different physicochemical behaviors in seawater.

A calibrated graphene-based chemi-sensor for sub parts-per-million NO2 detection operating at room temperature

Here, we present a room temperature operating chemi-sensor based on a graphene film that shows sensitivity to NO2 up to a 50 parts-per-billion (ppb) with extremely limited interference from relative humidity and can be also calibrated in a sub-parts-per-million (ppm) range with a response and recovery time of few seconds. The device has been fabricated using as active material, a solution of graphene nanosheets suspended in N-methyl-pyrrolidone drop casted on an alumina substrate with gold interdigitated electrodes. The derivative of the device response is found to be univocally correlated to NO2 concentrations from 100u2009ppb up to 1000u2009ppb and the sensor can therefore be calibrated in this same range.

The diverse toxic effect of SiO2 and TiO2 nanoparticles toward the marine microalgae Dunaliella tertiolecta

Nanoparticles (NPs) are widely used in many industrial applications. NP fate and behavior in seawater are a very important issue for the assessment of their environmental impact and potential toxicity. In this study, the toxic effects of two nanomaterials, silicon dioxide (SiO2) and titanium dioxide (TiO2) NPs with similar primary size (~20xa0nm), on marine microalgae Dunaliella tertiolecta were investigated and compared. The dispersion behavior of SiO2 and TiO2 NPs in seawater matrix was investigated together with the relative trend of the exposed algal population growth. SiO2 aggregates rapidly reached a constant size (600xa0nm) irrespective of the concentration while TiO2 NP aggregates grew up to 4u2009±u20095xa0μm. The dose–response curve and population growth rate alteration of marine alga D. tertiolecta were evaluated showing that the algal population was clearly affected by the presence of TiO2 NPs. These particles showed effects on 50xa0% of the population at 24.10 [19.38–25.43]u2009mgxa0L−1 (EC50) and a no observed effect concentration (NOEC) at 7.5xa0mgxa0L−1. The 1xa0% effect concentration (EC1) value was nearly above the actual estimated environmental concentration in the aquatic environment. SiO2 NPs were less toxic than TiO2 for D. tertiolecta, with EC50 and NOEC values one order of magnitude higher. The overall toxic action seemed due to the contact between aggregates and cell surfaces, but while for SiO2 a direct action upon membrane integrity could be observed after the third day of exposure, TiO2 seemed to exert its toxic action in the first hours of exposure, mostly via cell entrapment and agglomeration.

Comparative toxicity of nano ZnO and bulk ZnO towards marine algae Tetraselmis suecica and Phaeodactylum tricornutum

The wide use of ZnO nanoparticles in a number of products implies an increasing release into the marine environment, resulting in the need to evaluate the potential effects upon organisms, and particularly phytoplankton, being at the base of the throphic chain. To this aim, dose–response curves for the green alga Tetraselmis suecica and the diatom Phaeodactylum tricornutum derived from the exposure to nano ZnO (100xa0nm) were evaluated and compared with those obtained for bulk ZnO (200xa0nm) and ionic zinc. The toxic effects to both algae species were reported as no observable effect concentration (NOEC) of growth inhibition and as 1, 10, and 50% effect concentrations (EC1, EC10, and EC50). The toxicity decreased in the order nano ZnO > Zn2+ > bulk ZnO. EC50 values for nano ZnO were 3.91 [3.66–4.14] mg Zn/L towards the green microalgae and 1.09 [0.96–1.57] mg Zn/L towards the diatom, indicating a higher sensitivity of P. tricornutum. The observed diverse effects can be ascribed to the interaction occurring between different algae and ZnO particles. Due to algae motility, ZnO particles were intercepted in different phases of aggregation and sedimentation processes, while algae morphology and size can influence the level of entrapment by NP aggregates.This underlines the need to take into account the peculiarity of the biological system in the assessment of NP toxicity.

Characterization of Nanoparticles in Seawater for Toxicity Assessment Towards Aquatic Organisms

The fate and the behaviour of nanoparticles in seawater, which is the ultimate sink for any release of nanoparticles, is a very important issue for the assessment of their environmental impact. Despite this concern, only few studies regarding the ecotoxic effect of NPs upon marine organisms were conducted. In this work the dispersion behaviour of NPs in a seawater matrix has been investigated and their physicochemical properties characterized. The ecotoxicological impact towards marine organisms of several nanoparticles has been also examined.

TinyNose: Developing a wireless e-nose platform for distributed air quality monitoring applications

In this work we present the development and proof of concept testing of a protoype wireless e-nose (w-nose) architecture capable of mesh shaped networking. The proposed w-nose is based on a TelosB by Crossbow Inc. and custom, power aware, TinyOS based components for data gathering and local processing. Sensor nodes are equipped with a small array of nonconductive polymer/CB based chemiresistors operating at room temperature for VOCs indoor monitoring. A properly developed conditioning stage board connects the sensor array to the microcontroller ADC. A single w-nose has been tested in a controlled test chamber for terpenes discrimination, while networked motes operation have been demonstrated in ad-hoc small testing facilities for acetic acid spill detection.

An Holistic Approach to e-Nose Response Patterns Analysis—An Application to Nondestructive Tests

Artificial olfaction is an emerging application field for machine learning practitioners. In this paper, we propose a holistic approach to pattern classification in electronic noses applications. In particular, we show how classification results based on a complete measurement cycle can be combined with an assessment provided by real-time classifiers acting on the single instantaneous measurement sample. A running classification confidence measure allows for obtaining fast and reliable outcomes. A safety critical scenario has been selected for the testing of the proposed pattern analysis strategy involving the identification and discrimination of surface contaminants on composite panels in pre-bonding nondestructive tests during lightweight aircraft assembly. A reject option has been introduced to refuse low classification confidence panels improving both FP and FN rates. Results show how this strategy can efficiently exploit two different views of the electronic nose olfactive fingerprinting process that is currently seen as alternative.

Study of the correlation between sensing performance and surface morphology of inkjet-printed aqueous graphene-based chemiresistors for NO2 detection

The extremely high sensitivity to the external environment and the high specific surface area, as well as the absence of bulk phenomena that could interfere with the response signal, make graphene highly attractive for the applications in the field of sensing. Among the various methods for producing graphene over large areas, liquid phase exfoliation (LPE) appears to be very promising, especially if combined with inkjet printing (IJP), which offers several advantages, including the selective and controlled deposition of small ink volumes and the versatility of the exploitable inks and substrates. Herein we present a feasibility study of chemiresistive gas sensors inkjet-printed onto paper substrates, in which a LPE graphene suspension dispersed in a water/isopropanol (H2O/IPA) mixture is used as sensing ink. The device performances, in terms of relative conductance variations, upon exposure to NO2 at standard ambient temperature and pressure, are analysed. In addition, we examine the effect of the substrate morphology and, more specifically, of the ink/substrate interaction on the device performances, by comparing the response of different chemiresistors fabricated by dispensing the same suspension also onto Al2O3 and Si/SiO2 substrates and carrying out a supportive atomic force microscopy analysis. The results prove the possibility to produce sensor devices by means of a wholly environmentally friendly, low-cost process that meets the requests coming from the increasing field of paper-based electronics and paving the way towards a flexible, green-by-design mass production.

Sub-PPM Nitrogen Dioxide Conductometric Response at Room Temperature by Graphene Flakes Based Layer

The two-dimensional nature of graphene, allowing a total exposure of all its atoms to the adsorbing gas molecules, provides the greatest sensor area per unit volume and outlines the possibility to employ this material as a powerful sensing layer. The synthesis and manipulation of graphene as well as the device fabrication are still challenging due to several technological limits. In the present work we report on a simple approach to fabricate chemiresistive sensors based on chemically exfoliated natural graphite. The devices show the ability to detect a toxic gas, such as NO2, down to few ppb at room temperature in controlled environments.