Correction: Alfano et al. A Review of Low-Cost Particulate Matter Sensors from the Developers' Perspectives. Sensors 2020, 20, 6819.

The authors wish to make the following corrections to this paper [...].

A Wearable Low-Power Sensing Platform for Environmental and Health Monitoring: The Convergence Project.

The low-power sensing platform proposed by the Convergence project is foreseen as a wireless, low-power and multifunctional wearable system empowered by energy-efficient technologies. This will allow meeting the strict demands of life-style and healthcare applications in terms of autonomy for quasi-continuous collection of data for early-detection strategies. The system is compatible with different kinds of sensors, able to monitor not only health indicators of individual person (physical activity, core body temperature and biomarkers) but also the environment with chemical composition of the ambient air (NOx, COx, NHx particles) returning meaningful information on his/her exposure to dangerous (safety) or pollutant agents. In this article, we introduce the specifications and the design of the low-power sensing platform and the different sensors developed in the project, with a particular focus on pollutant sensing capabilities and specifically on NO2 sensor based on graphene and CO sensor based on polyaniline ink.

A Review of Low-Cost Particulate Matter Sensors from the Developers' Perspectives.

The concerns related to particulate matter's health effects alongside the increasing demands from citizens for more participatory, timely, and diffused air quality monitoring actions have resulted in increasing scientific and industrial interest in low-cost particulate matter sensors (LCPMS). In the present paper, we discuss 50 LCPMS models, a number that is particularly meaningful when compared to the much smaller number of models described in other recent reviews on the same topic. After illustrating the basic definitions related to particulate matter (PM) and its measurements according to international regulations, the device's operating principle is presented, focusing on a discussion of the several characterization methodologies proposed by various research groups, both in the lab and in the field, along with their possible limitations. We present an extensive review of the LCPMS currently available on the market, their electronic characteristics, and their applications in published literature and from specific tests. Most of the reviewed LCPMS can accurately monitor PM changes in the environment and exhibit good performances with accuracy that, in some conditions, can reach R2 values up to 0.99. However, such results strongly depend on whether the device is calibrated or not (using a reference method) in the operative environment; if not, R2 values lower than 0.5 are observed.

Early ecotoxic effects of ZnO nanoparticle chronic exposure in Mytilus galloprovincialis revealed by transcription of apoptosis and antioxidant-related genes.

Recently, China became one of the largest nanomaterial markets in the world. The wide use of ZnO nanoparticles in a number of products implies an increasing release in marine environment and consequently the evaluation of the potential effects upon marine organisms largely cultured in China for commercial purposes, such as invertebrate bivalves is a current need. To this aim, survival, bioaccumulation, and transcription pattern of key genes, p53, PDRP, SOD, CAT, and GST, involved in DNA damage/repair and antioxidation, in Mytilus galloprovincialis digestive gland, exposed to ZnO NPs (<100 nm) and ZnO bulk (150-200 nm) for 4 weeks, were evaluated. ZnSO4 was also assessed to appraise the role of zinc ions. Starting from 72 h, increasing mortality values along the exposure time were observed for all ZnO compounds. The highest difference was evident after 28 d when NPs resulted three times more toxic than bulk, (LC50) = 0.78 mg Zn/L (confidence limits: 0.64, 1.00) and 2.62 mg Zn/L (confidence limits: 1.00, 4.00), respectively. For ZnSO4 the (LC50) was always the lowest reaching the minimum value at 28 d 0.25 mg Zn/L (confidence limits: 0.10-0.40). Digestive gland showed higher uptake rate of ionic Zn respect to ZnO NPs and bulk during the first three days of exposure. In particular at the end of the exposure time (28 d) at 1 mg Zn/L the rank of Zn uptake rate was Zinc ion > ZnO NPs > ZnO bulk. The relative expression of investigated genes evidenced that distinct actions of apoptosis and antioxidation occurred in M. galloprovincialis exposed to ZnO NPs with a peculiar pattern dependent on exposure time and concentration. Application of the qRT-PCR technique revealed evidence of sensitivity to the nanomaterial since the first time of exposure.

Electronic Noses for Composites Surface Contamination Detection in Aerospace Industry.

The full exploitation of Composite Fiber Reinforced Polymers (CFRP) in so-called green aircrafts design is still limited by the lack of adequate quality assurance procedures for checking the adhesive bonding assembly, especially in load-critical primary structures. In this respect, contamination of the CFRP panel surface is of significant concern since it may severely affect the bonding and the mechanical properties of the joint. During the last years, the authors have developed and tested an electronic nose as a non-destructive tool for pre-bonding surface inspection for contaminants detection, identification and quantification. Several sensors and sampling architectures have been screened in view of the high Technology Readiness Level (TRL) scenarios requirements. Ad-hoc pattern recognition systems have also been devised to ensure a fast and reliable assessment of the contamination status, by combining real time classifiers and the implementation of a suitable rejection option. Results show that e-noses could be used as first line low cost Non Destructive Test (NDT) tool in aerospace CFRP assembly and maintenance scenarios.

Geographical origin of durum wheat studied by 1H-NMR profiling.

(1)H-Nuclear magnetic resonance (NMR) spectroscopy was used to detect metabolic profiles of wheat flour samples of different geographical and botanical origin. The NMR profiles were analyzed by multivariate statistical techniques in order to establish the origin of the samples. A linear model, able to discriminate among three different locations, was built achieving a prediction level of about 80% of correctly assigned samples. The principal classes of compounds responsible for the geographic origin discrimination were individuated in aromatic compounds and amino acids. The statistical modeling also indicated that botanical origin information is very poor in the NMR profiles of the analyzed wheat samples.

Toxicological effects of transition metal-doped titanium dioxide nanoparticles on goldfish (Carassius auratus) and common carp (Cyprinus carpio).

The aim of present study was to assess the toxicological effects of transition metal-doped titanium dioxide nanoparticles (TiO2 NPs) on histopathological changes, behavioral patterns, and antioxidant responses of goldfish (Carassius auratus) and common carp (Cyprinus carpio). The synthesized nanoparticles were confirmed by Transmission Electron Microscopy, Field Emission Scanning Electron Microscopy, X-ray diffraction, UV-visible, and Vibration Sample Magnetometer. Fish in four experimental groups exposed to sub-lethal concentrations of pure TiO2 NPs (10 mg L-1), chromium (Cr), iron (Fe), and nickel (Ni) doped TiO2 NPs for seven days. Statistical analysis of oxidative stress responses in gills showed significant differences in superoxide dismutase, total antioxidant capacity, and malondialdehyde parameters between two species and in all parameters than glutathione peroxidase between experimental groups and control group. In intestine, no significant difference was observed among groups, but oxidative responses were markedly different in all parameters among fish species. The histopathological analysis showed hyperplasia, fusion, and aneurism in the gills as well as degeneration, integration of villi, necrosis and erosion of the intestine. Our findings indicated that compare to pure TiO2 NPs, exposure to transition metals-doped TiO2 NPs induced oxidative stress and histopathological changes in both fish species.

Different sizes of ZnO diversely affected the cytogenesis of the sea urchin Paracentrotus lividus.

Today nanoparticles (NPs) have many applications in commercial products due to their small size and peculiar properties that, conversely, make them potentially toxic for humans and the environment. ZnO NPs are largely used in many personal care products, such as sunscreens and cosmetics. In this study the cytotoxic effects of ZnO particles with different sizes (ZnO Bulk, >100nm; ZnO NPs, 100nm and ZnO NPs, 14nm) upon the first developmental stages of the sea urchin Paracentrotus lividus, are evaluated. Morphological alterations are also assessed by embryotoxicity tests. The cytogenetic analysis highlighted that ZnO NPs interfere with cell cycle inducing a dose-dependent decrease of mitotic activity and chromosomal aberrations at higher concentrations (30µM). Moreover, the larval development was affected by ZnO NPs 100nm (EC50=0.46 [0.30-0.63] µM [Zn]) in a dose-dependent way. Size-dependent toxicity was instead not obtained for ZnO NPs. From our results could be highlighted that the presence of embryos, blocked in pre-larval stage, could be due to the induction of chromosome aberrations by ZnO particles, confirming that cytogenetic analyses allow evaluating possible NPs action mechanisms.

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 (100 nm) were evaluated and compared with those obtained for bulk ZnO (200 nm) 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.

CVD transfer-free graphene for sensing applications.

The sp2 carbon-based allotropes have been extensively exploited for the realization of gas sensors in the recent years because of their high conductivity and large specific surface area. A study on graphene that was synthetized by means of a novel transfer-free fabrication approach and is employed as sensing material is herein presented. Multilayer graphene was deposited by chemical vapour deposition (CVD) mediated by CMOS-compatible Mo. The utilized technique takes advantage of the absence of damage or contamination of the synthesized graphene, because there is no need for the transfer onto a substrate. Moreover, a proper pre-patterning of the Mo catalyst allows one to obtain graphene films with different shapes and dimensions. The sensing properties of the material have been investigated by exposing the devices to NO2, NH3 and CO, which have been selected because they are well-known hazardous substances. The concentration ranges have been chosen according to the conventional monitoring of these gases. The measurements have been carried out in humid N2 environment, setting the flow rate at 500 sccm, the temperature at 25 °C and the relative humidity (RH) at 50%. An increase of the conductance response has been recorded upon exposure towards NO2, whereas a decrease of the signal has been detected towards NH3. The material appears totally insensitive towards CO. Finally, the sensing selectivity has been proven by evaluating and comparing the degree of adsorption and the interaction energies for NO2 and NH3 on graphene. The direct-growth approach for the synthesis of graphene opens a promising path towards diverse applicative scenarios, including the straightforward integration in electronic devices.

Toxic effects of ZnO nanoparticles towards marine algae Dunaliella tertiolecta.

Dose response curve and population growth rate alterations of marine Chlorophyte Dunaliella tertiolecta derived from the exposure to ZnO nanoparticles were evaluated. Bulk ZnO and ionic zinc were also investigated for comparison. At the same time, the aggregation state and particle size distribution were monitored. The evaluated 50% effect concentration (EC50 1.94 [0.78-2.31] mg Zn L(-1)) indicates that nano ZnO is more toxic than its bulk counterpart (EC50 3.57 [2.77-4.80] mg Zn L(-1)). Cross-referencing the toxicity parameters calculated for ZnCl(2) (EC50 0.65 [0.36-0.70] mg Zn L(-1)) and the dissolution properties of the ZnO, it can be gathered that the higher toxicity of nano ZnO is most likely related to the peculiar physicochemical properties of the nanostate with respect to the bulk material. Furthermore growth rate of D. tertiolecta was significantly affected by nano ZnO exposure. Our findings suggest that the primary particle size of the dispersed particles affect the overall toxicity.

Embryotoxicity and spermiotoxicity of nanosized ZnO for Mediterranean sea urchin Paracentrotus lividus.

The effect of nano ZnO (nZnO) upon the fertilization and early development of embryos of the Mediterranean sea urchin Paracentrotus lividus is reported herein for the first time. Zn ion (ZnCl2) and bulk ZnO (bZnO) toxicity were assessed for comparison. The embryotoxicity tests showed a 100% effect already at 1 µM of nZnO (expressed as [Zn]) while bZnO and ZnCl2 showed EC50s of 0.98 [0.88-1.19] µM [Zn] and 2.02 [1.97-2.09] µM [Zn], respectively. Noteworthy, the frequency of developmental defects for the three compounds was dissimilar and a specific trend for larval skeletal abnormality produced by nZnO was observed. The sperm fertilization capability was only slightly affected by the tested chemicals while the effects were dramatic on the offspring quality of sperms exposed to ZnO compounds resulting in an early block of the regular larval development. ZnO toxicity seems related not only to Zinc ions but also to some surface interactions of particle/aggregates with target organisms and/or with the seawater.

Investigation of ZnO nanoparticles' ecotoxicological effects towards different soil organisms.

INTRODUCTION: Nanomaterials have widespread applications in several industrial sectors. ZnO nanoparticles (NPs) are among the most commonly used metal oxide NPs in personal care products, coating and paints. However, their potential toxicological impact on the environment is largely unexplored. MATERIALS AND METHODS: The aim of this work was to evaluate whether ZnO nanoparticles exert toxic and genotoxic effects upon terrestrial organisms: plants (Lepidium sativum, Vicia faba), crustaceans (Heterocyipris incongruens), insects (Folsomia candida). To achieve this purpose, organisms pertaining to different trophic levels of the soil ecosystem have been exposed to ZnO NPs. In parallel, the selected soil organisms have been exposed to the same amount of Zn in its ionic form (Zn(2+)) and the effects have been compared. RESULTS: The most conspicuous effect, among the test battery organisms, was obtained with the ostracod H. incongruens, which was observed to be the most sensitive organism to ZnO NPs. The root elongation of L. sativum was also mainly affected by exposure to ZnO NPs with respect to ZnCl(2), while collembolan reproduction test produced similar results for both Zn compounds. Slight genotoxic effects with V. faba micronucleus test were observed with both soils. CONCLUSION: Nanostructured ZnO seems to exert a higher toxic effect in insoluble form towards different terrestrial organisms with respect to similar amounts of zinc in ionic form.