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In this work, we illustrate an autonomous and real-time reconfigurable classifier. The algorithm starts from a non-adaptive classifier and evolves during the routine operation of sensors providing a dynamic optimization of the feature selection and refinement of classes’ distribution. The model has been tested on an experimental dataset and the results show that the algorithm may improve the resilience of classifiers in case of drifting and/or faulty sensors. The outcome of this studied case suggests that the algorithm might be able to enhance long-term performance almost independently from which classification model is considered. [ABSTRACT FROM AUTHOR]

Porphyrins are the natural candidates to the detection of carbon monoxide however the physical properties of solid-state layers of porphyrins limit their use as gas sensors mainly with mass and optical transducers. Recently we shown that the photonic properties of porphyrins, brilliantly exploited in organic solar cells, can lead to a new class of photo-activated sensors made by porphyrins coated metal oxides. Here we investigate the sensitivity to carbon monoxide of resistive sensors made by zinc oxide nanoparticles coated by a porphyrin layer. Sensors were prepared following two different routes and tested, at room temperature and in various light conditions, to CO and few volatile compounds. Results show a significant sensitivity and selectivity to CO. [ABSTRACT FROM AUTHOR]

Photoconductivity and gas sensitivity cooperate in porphyrins coated ZnO nanostructures. However, in organic coated semiconductors the former is regulated by a number of mechanisms, involving the charge transfer in the organic layer. Since organic layers are poor conductors these processes are quite slow and the sensor may exhibits a long time drift before to be operative as gas sensor. In this paper we show that under light modulation, the carrier frequency component of the signal is free of drift and it can readily indicate the interaction with volatile compounds. [ABSTRACT FROM AUTHOR]

Abstract: Gas sensor arrays can be very sensitive to the properties of individual sensors, then even the fault of one of the array element can greatly jeopardize the array performance. Sensor replacement easily achieves the pristine conditions but non reproducibility between sensors of the same series may also require a new calibration. In this paper, a processing strategy aimed at counteracting the necessity of new calibration is introduced. It is based on an ensemble of adaptive classifiers each built with single sensors data. The array prediction is then obtained by a majority voting decision rule based on the outputs of the ensemble of models. The classifier has been tested with an experiment aimed at detecting gases with a drifting gas sensors array. The classifier performance has been compared with a standard classifier. [Copyright &y& Elsevier]

Abstract: In this paper we study the sensitivity to volatile organic vapors of the surface potential of metalloporphyrins coated ZnO nanorods. The hybrid material has been growth with an original method based on the direct addition of metalloporphyrins to the hydrothermal precursor solution. The resulting film shows a complete coating of the ZnO surface expected to improve the photovoltaic characteristics. The chemical sensitivity of the surface potential has been measured in dark and in white light illumination. For sake of comparison, the hybrid material has been compared with those obtained from a casting coated porphyrin functionalized ZnO nanorods. Results show that the material preparation strongly influences the sensor properties, and in case of the hybrid material the illumination with visible light elicits an increase of the sensor response that is proportional to the ability of the volatile compound to donate electrons. [Copyright &y& Elsevier]

Abstract: Optical methods combine the wide availability of molecular indicators with simple and contactless measurements. In this context, indicator-displacement assay is a viable strategy for developing optical chemosensors with synthetic receptors. Such approach may be used to overcome the limits of sensing molecules and to widen the range of detectable compounds. In this paper, it is shown that proper blends of porphyrins and Lewis acid-base indicators can give rise to sensitive units whose properties exceed those of single components. [Copyright &y& Elsevier]

Abstract: In this work, gas sensing properties of monocarboxy tetraphenylporphyrin functionalized ZnO nanorods under different light illumination, were investigated. These studies showed that the sensitivity to triethylamine of porphyrin functionalized ZnO nanorod device are greatly enhanced under illumination with visible light. This photoactivated nanostructure composition has the potential for gas sensor device applications. [Copyright &y& Elsevier]

Abstract: Sensors are the less durable parts in any chemical sensor system, then the replacement of sensors maintaining hardware and data processing is a necessity in real applications. Though sensors replacement requires a perfect reproducibility of the sensors fabrication. Among the different sensor technologies, those based on optical transduction may offer a straightforward methodology to release the requirement of identical sensor manufacturing. In particular it will be shown here that the use of image sensor provides a surprising parallel with natural olfaction. An important consequence is that the data processing is independent from the geometric arrangement of the sensitive layer. This feature leads to a simple sensor layer replacement and to a prompt arrangement of different sensor systems, even remotely located, into a single data processing system. [Copyright &y& Elsevier]

Summary: Optical sensors based on image acquisition hardware represent a promising technique to measure the chemical composition of an environment or the headspace generated by complex samples. However, this approach is still limited by the fact that only a restricted kind of interactions may change the visible spectrum of an indicator. As a consequence, the receptive field, namely the amount of different chemicals that can be captured by an opto-chemical sensor, is rather restricted. To extend the application of optical indicators we propose to use blends of porphyrins and acid-base indicators as materials for opto-chemical sensors. A suitable choice of the components allows to obtain sensing features that are not correlated to those of the single constituents. This strategy provides a straightforward method to develop sensor arrays for a wide number of practical applications, among them it is investigated here the measure of emissions from human skin. [Copyright &y& Elsevier]

Astroni volcano in the Campi Flegrei caldera (southern Italy) is a 2 km wide, densely vegetated tuff ring and hosting several volcanic structures, including tuff cones, scoriae cones, lava domes, and three small lakes. Geochemical data of waters and dissolved gases from the lakes, coupled with microbiological analyses on lake water and sediments, were used to shed light on the possible relationship between the lakes and the hydrothermal fluid circulation system as suggested by previous geophysical surveys. Water chemistry was dominated by solutes, mainly Na+ and HCO 3 −, deriving from fluids and CO 2 -rich gases typically found in discharges located at the periphery of hydrothermal-volcanic systems. Lago Grande (LG) lake showed an anoxic hypolimnion with abundant non-atmospheric dissolved gases, consisting of biogenic CH 4 and CO 2 , the latter having a twofold origin, biogenic and hydrothermal. The occurrence of anaerobic methanotrophs coupled with the lack of hydrogenotrophic methanogenic archaea along the whole vertical profile of LG suggested that CH 4 was mostly produced from degradation of abundant terrestrial organic matter within the deep lake sediments, and then consumed during its diffusion through the lake. Notwithstanding, the output rate of CH 4 from LG surface was anomalously high relative to those commonly measured in lakes. Carbon dioxide from the hydrothermal source and produced by CH 4 oxidation was partially fixed in the lake via the acetyl-CoA pathway. Accordingly, the CO 2 fluxes from the LG surface were relatively low, in the range of those measured in volcanic lakes dominated by biogenic CO 2. The dependence of the chemistry of the Astroni lakes on inputs from the Campi Flegrei hydrothermal system, besides on biogeochemical processes, offers a possible explanation for the anomalous increase of the LG water level occurred in the last years, which was not consistent with the recorded local rainfall but likely caused by an increasing hydraulic pressure related to the enhanced hydrothermal activity recorded at Campi Flegrei in the last decades. According to this hypothesis, the future evolution of the current volcanic unrest may govern the fate of the lake water level with important implications for the functioning of the precious Astroni ecosystem. • The chemistry of Astroni lakes depends on volcanic fluid inputs. • Methanogens and methanotrophs likely control non-atmospheric dissolved gases. • The increase of Astroni Grande lake volume is caused by increasing volcanic fluid input. • The fate of the Astroni lakes is linked to the volcanic activity of Campi Flegrei. • The Astroni ecosystem may suffer the influence of increasing volcanic fluid input. [ABSTRACT FROM AUTHOR]