Analyses of odours from concentrated animal feeding operations: a review

Concentrated Animal Feeding Operations (CAFOs) are widely present all over the world due to the high population demand for food and products of animal origin. However, they have generated several environmental concerns, including odour nuisance, which affects people health and quality of life. Odours from livestock are a very complex mixtures of molecules and their analytical investigation is highly demanding. Many works have been published regarding the study of odours from CAFOs, using different techniques and technologies to face the issue. Thus, the aim of this review paper is to summarize all the ways to study odours from CAFOs, starting from the sampling methods and then treating in general the principles of Dynamic Olfactometry, Gas Chromatography coupled with Mass Spectrometry and Electronic Noses. Finally, a deep literature summary of Gas Chromatography coupled with Mass Spectrometry and Electronic Noses applied to odours coming from poultry, dairy and swine feeding operations is reported. This work aims to make some order in this field and it wants to help future researchers to deal with this environmental problem, constituting a state-of-the-art in this field

ADVANCED MATERIALS FOR ELECTRODE MODIFICATION IN TRACE ELECTROANALYSIS

Trace analysis [1] (i.e. the analysis of analytes in concentration low enough to cause difficulty, generally under 1 ppm) albeit very challenging, in the last years has shown a tremendous growth, prompted by the urgent need of many International Organizations (US Environmental Protection Agency EPA, U.S. Food and Drug Administration FDA, European Food Safety Authority EFSA, World Health Organization WHO) looking for new analytical techniques for the detection of different molecules in different and increasingly more complex matrixes. Trace analysis is therefore a basic and fundamental technique in many scientific and technological areas, from the environmental monitoring, the food safety and the clinical diagnosis to the national security and the forensic investigation. The determination of trace analytes requires reliable and robust analytical methods characterized by high level of sensitivity, precision, accuracy, selectivity and specificity. Among different analytical techniques suitable for this purpose, such as mass spectrometry, which is characterized by high accuracy and sensitivity and low limits of detection, electroanalytical techniques and particularly those based on pulsed voltammetry, seem to be a promising independent alternative in terms of very high precision, accuracy and sensitivity, simplicity of use, portability, easy automation and possibility of on-line and on-site monitoring without sample pre-treatments and low costs. These methods are no more confined to the detection of inorganic species and have been already and successfully employed for the determination of organic compounds and environmental carcinogens [2, 3, 4], as the Jir\ued Barek UNESCO Laboratory of Environmental Electrochemistry and the Trace Element Satellite Centre haves amply demonstrated in the last decades. In this context, two quite recent technological developments have enhanced the chances of progress and growth of electroanalitycal methodologies for trace analysis: \u2022 the screen-printing microfabrication technology [5, 6], which offers the possibility of large-scale mass production of extremely inexpensive, disposable and reproducible electrochemical sensors increasing the potentialities of the voltammetric techniques, since it allows to work with small amounts of samples, considerably reducing the analytical costs and facilitating on-line and on-site monitoring; \u2022 the use of nanosized and/or nanostructured materials sometimes combined with the use of polymeric materials for the modification of electrodes, with the aim of increasing the affinity for the analyte, increasing sensitivity, lowering the limits of detection and minimizing or completely avoiding interferences. This PhD thesis has sought to provide a contribution in this framework, trying to enhance the technological potentialities of electroanalytical methodologies in the field of inorganic and organic trace analysis, with the use of screen-printed electrodes and electrodes modified by nanomaterials and/or polymeric membranes. SCREEN-PRINTED electrodes Different types of screen-printed electrodes (SPEs) were employed for the determination of organic and inorganic carcinogenic hazardous compounds, included in the Priority Pollutants List of many countries. In particular, the following analytes have been the subject of the study: furan, benzidines, chromium and arsenic. Furan, a volatile oxygen-containing heterocyclic compound, was classified as a possible human carcinogen by the International Agency for Research on Cancer (IARC) in 1995, with the liver as primary target organ. It is unintentionally produced, together with dioxin, during most forms of combustion. For this reason, it falls into the Organic Persistent Pollutants list of Stockholm Convention. It is also formed during the thermal degradation of carbohydrates in foods [7], such as jarred baby foods, coffee, canned meat and toasted bread. The standard analytical procedure [8] for the detection of furan is based on GC/MS, which reaches the very low detection limits required by the analytical problem, but it is affected by results overestimation since furan can be produced during the heating required by the technique. A new electroanalytical method based on Square Wave Voltammetry (frequency of 100-200 Hz) at Pt disk and Pt-SPE covered by Nafion was studied. Furan shows an oxidation peak in acetonitrile at 1.85-1.95 V (SCE) for Pt disk and 1.95 V (SCE) for Pt-SPE. Both electrodes display a good linear correlation in the dynamic range between 1.02 ppm and 68.07 ppm. Pt disk presents a problem of saturation for higher concentration. The detection limits are quite good (0.11 ppm for Pt disk and 0.52 ppm for Pt-SPE), while apparent recovery factors (in both cases > 95%) are better than those determined for the conventional GC/MS method. The applicability of the new method in a real matrix was tested using Pt-SPE covered with Nafion membrane for experiments in coffee, spiked with known quantities of furan. Good calibration plot (R2 = 0.997) and apparent recovery factor (102 %) were obtained also in this case. Benzidine is an organic synthetic compound which exists as an odourless, white or slightly reddish crystalline solid and that evaporates slowly, especially from water and soil. Benzidine and its derivatives are employed in many fields but the main use remains the synthesis of azo-dyes, by coupling benzidine with phenols and amines [9], which are widely employed in textile, printing, leather, paper making, drug and food industries and can be released in the effluents and wastewaters. Benzidine was identified as a carcinogenic agent [10] for human urinary bladder by IARC because its oxidation by human enzymes can permit its binding with DNA. Furthermore, its derivatives generate benzidine through reduction by intestinal and environmental microorganisms. Though production and use of azo-dyes were forbidden in many countries since 1970s, their use in companies of emerging countries is still increasing, thus affecting the work place of many environments. Electrochemical techniques for the detection of benzidine were tested at standard electrodes (Platinum and GC) with promising results [11, 12]. Benzidine and its derivatives (o-tolidine, o-toluidine, tetrametylbenzidine) were detected by Differential Pulse Voltammetry (DPV) using Carbon-based Screen-Printed Electrodes (C-SPE) in comparison with Glassy Carbon electrodes. Cyclic voltammograms of these molecules show that the reaction is a bielectronic chemical and electrochemical reversible one for benzidine, o-tolidine and tetrametylbenzidine, while it is monoelectronic and irreversible for o-toluidine. The four molecules display different peak potential position, due to the presence or absence of electrodonating groups, tetrametylbenzidine characterized by the lower peak potential, followed by o-tolidine, benzidine and finally o-toluidine. In the case of the detection with DPV and C-SPE, all molecules show excellent linearity in the linear dynamic range 2 ppb-18 ppb (R2 > 0.9), high accuracy (with apparent recovery factors very close to 100%) and very low detection limits (0.33 ppb for benzidine, 1.45 ppb for tetrametylbenzidine, 0.43 ppb for o-tolidine and 123 ppb for o-toluidine). Since the innovative technique seems to be very reliable and each molecule presents a different peak position, an interesting research development was the study of the behaviour of the mixture of the four molecules. Cyclic voltammograms show that they can be revealed at the same time and that their response remains linear and with a good correlation (R2 > 0.99), also when they are present contemporaneously. Preliminary results using DPV display four observable peaks. Chromium, particularly its hexavalent species, is a carcinogenic and mutagenic pollutant and it is located in the Priority Pollutants List of many countries. It is employed in several industrial processes (metal plating, leather tanning, paint making) and it can be especially found in waste waters. Therefore, in recent years, many efforts have been made to develop efficient and accurate techniques for its determination [13]. For this purpose mercury electrodes are widely used in association with voltammetric stripping techniques preceded by cathodic or anodic preconcentration steps, especially in the presence of chromium complexing agents. Nowadays, mercury tends to be replaced by other less toxic materials [14]. A promising alternative seems to be the environmentally friendly bismuth electrode [15, 16], since it presents an electrochemical behaviour very similar to mercury, in particular in the wide cathodic potential window. Commercially available bismuth Screen-Printed Electrodes (Bi-SPE) were employed using Square Wave Voltammetry (SWV) to develop a new technique for the detection of Cr(VI), using pyrocatechol violet (PCV) as Cr(VI) complexing agent and electroactive probe and HEDTA as Cr(III) complexing agent to remove possible Cr(III) interferences. This innovative method was compared with the traditional procedure based on Differential Pulse Adsorptive Stripping Voltammetry (DPAdSV) at Hanging-Mercury Drop Electrode (HMDE). Many differences can be envisaged: first of all, PCV displays at Bi-SPE an intensive reduction peak at -1.18 V, which increases for consecutive additions of Cr(VI), in contrast with the decrease observed in the case of HMDE in the same conditions. This behaviour can be explained assuming that the complex Cr(VI)-PCV is electroactive at Bi-SPE and non-electroactive at HMDE. Secondly, PCV at Bi-SPE can be revealed without stripping, which is instead a necessary step required when adopting HMDE. The new method shows a very good linearity range (R2 = 0.996) and accuracy (Apparent Recovery Factors around 102%) and its limit of detection is an order of magnitude lower than that using HMDE (0.28 ppb against 2.8 ppb). The applicability of the new optimized procedure was tested analyzing samples coming from Cr(VI) photocatalysis in liquid phase to follow the photoreduction of Cr(VI) from a concentration of 2.8 ppm to the complete disappearance. The analysis was performed with an analyte addition method (three addition of the sample) after a calibration plot built with 8 standard additions. This method allows distinguishing the performances of different types of photocatalysts. The same test was also performed at HMDE for comparison: the new technique displays better results since it is less affected by interferences of the complex matrix. Arsenic is a hazardous, dangerous and toxic compound, especially in its trivalent form, and arsenic contamination is widely recognized as a global health problem, ascribing it in the first places of the Priority Pollutants List. High levels of As can be found in soil, groundwater and drinking water, since arsenic derivatives are mainly used in agricultural poisons, such as fungicides, insecticides, pesticides. Chronic arsenic exposure can cause a lot of health diseases, such as skin lesions, cancers, cardio-vascular system problems. For these reasons, many methods characterized by pros and cons are present in the Literature for As detection [17]. In this work, Gold-based screen-printed electrodes (Au-SPE) were used for the determination of As by Linear Sweep Voltammetry with a preconcentration step and a cleaning procedure. Citric acid was employed as supporting electrolyte instead of hydrochloric acid, which caused electrode damaging, and good calibration plots were obtained in the range 4.9-59 ppb, in particular for gold nanoparticles-based screen-printed electrodes. The optimized method was applied to As detection during its photocatalytic oxidation by titanium dioxide, allowing to discriminate among different types of photocatalysts. ELECTRODES modified by NANOMATERIALS An important advantage of electroanalytical techniques is the possibility to modify the working electrode with different types of advanced materials to increase the affinity for the analyte, to lower the limits of detection and to avoid interferences. In particular, during the last years, nanomaterials appeared to be very promising for application in the field of sensors and biosensors. Among different types of nanomaterials, carbon nanotubes, metal and semiconductive nanoparticles, show very interesting properties and features for electrochemical performances and were chosen for the modification of electrodes to be used in selected trace electroanalytical applications. All the new modified electrodes were firstly characterized and studied by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS), in the presence or in the absence of a model probe molecule, in order to obtain important information about electrochemical properties and the behaviour of the electrode in solution and with the redox probe. After the characterization study, some electrodes were used as sensors for the determination of relevant compounds or pollutants at trace level. Carbon nanotubes (CNT) [18, 19] are extensively employed in the electroanalytical field, due to their large surface area, electrocatalytic activity, fast electron transfer rate and easy functionalization. Since the procedure of purification with acids plays an important role for electrode performance, initially, a detailed study on different purification procedures was performed. 24 h sulfonitric mixture treatment appeared to be the best procedure for our CNTs yielding to materials characterized by an high metal nanoparticles removal, high amount of covalent acidity (responsible of CNTs activity), high surface area and mesoporosity. Moreover, the final removal of amorphous carbon by NaOH treatment highly improved the reversibility of the final electrodic device and favoured the diffusion mechanism of the process. The best type of purified and activated CNTs was employed for applications in electroanalysis, in particular in the determination of some previously studied pollutants: o-toluidine, benzidine and furan. o-toluidine was detected using Linear Sweep Voltammetry in the range 1.5-7 ppm with good correlation, obtaining a limit of detection of 0.16 ppm and excellent apparent recovery factors and repeatability, in comparison with carbon based-screen printed electrodes, which presented problems of fouling, probably due to polymerization products. This new method was used for the determination of o-toluidine during its photodegradation mediated by ZnO photocatalyst, showing better performances than C-SPE and comparable with HPLC. Moreover, the methodology was also employed to monitor o-toluidine absorption by cyclodextrine nanosponges based on hydrogel polyamidoamines (PAA), allowing to discriminate among various types of resins and to obtain absorption kinetic parameters. Benzidine was determined by using Square Wave Voltammetry in the range 0.05-2.2 ppm, obtaining good correlation and good limits of detection at ppb level, with better apparent recovery factors and repeatability in comparison with the previously optimized technique based on C-SPE. In the case of furan, preliminary promising results were obtained with deposition of Pt nanoparticles on carbon nanotubes by cyclic voltammetry, but optimization of nanoparticles deposition procedure and application of other voltammetric techniques are still needed and are currently under investigation. Metal and semiconductor nanoparticles [20] present unique peculiar properties, dependent on their size and shape, very different from bulk materials, such as high active surface area, high surface-to-volume ratio, selectivity, easy functionalization and electrocatalysis, and for these reasons they are extensively employed in electroanalysis. In this work, gold, silver and titanium dioxide nanoparticles were studied and characterized. Gold nanoparticles, synthesized by colloidal procedure with or without a protective polymer on carbon nanotubes as support, showed in comparison with CNTs, an increase in the peak current and capacitance, followed by the decrease of charge transfer resistance. The polymer, if the content of gold is low, is detrimental for the electrochemical behaviour, probably because it isolates too much the gold nanoparticles. The best results were obtained with 1% Au or 5% Au-Polymer. The optimized electrode was tested for the determination of glycerol obtaining really promising preliminary results using cyclic voltammetry. Silver nanoparticles were synthesized via colloidal method using two different supports: Nafion membrane and carbon nanotubes. In the case of Nafion, Ag nanoparticles show higher current intensity than bare electrode, probably due to higher surface area, a change in the diffusion mechanism from planar to convergent and small double layer formation. This electrode was tested for the determination of halothane and dichloromethane, showing promising preliminary results. In the case of CNTs, silver nanoparticles allowed the extension of the potential range towards negative values and peak currents were higher than the previous case with Nafion, showing the important contribute played by CNTs. Moreover, the use of a protective polymer (PVA) caused the decrease of the electrode activity, probably due to less available Ag nanoparticles. Titanium dioxide nanorods were studied in combination with single-walled carbon nanotubes, in the dark or under UV illumination, considering the photoactivity of titania. The best electrochemical performances were obtained for SWCNTs, since titania, as semiconductor brings a more resistive behaviour. Differences between dark and irradiation appeared only in the presence of titania, as expected. UV irradiation caused a change in the model probe molecule diffusion through the nanomaterials, probably ascribable to excited electrons of the titanium dioxide. ELECTRODES modified by POLYMERIC MEMBRANES Conducting polymers are polymeric systems characterized by ionic conductivity. They can be divided into two classes: electron and proton conducting polymers. Electron conducting polymers present a conjugated chain structure, with an extended \u3c0-bond system, leading to the formation of broad valence and conduction bands. Among all the types of electron conducting polymers, electroactive polymers seem to have the best qualities for the construction of sensors [21, 22, 23]. Indeed, they can act as electron donors/acceptors, adding to the high conductivity, an electrocatalytic effect and a possibility of redox-mediation, showing both electronic and ionic conductivity in contact with the electrolyte solution. Brilliant Green (BG), belonging to the triphenylmethane family, was chosen as electroactive polymer for the production of modified electrodes, in combination with CNTs and PEDOT [24], another non-redox electron conducting polymer. CNTs in combination with PEDOT gave the best electrochemical performance in terms of capacitance and low resistance, but when the determination of hydrogen peroxide was considered, electrode with CNTs and polyBG gave the best results for the presence of the redox centre (LoD around 30 ppb). This electrode was also tested as biosensor for glucose and ethanol, immobilizing on the electrode glucose oxidase (GOx) and alcohol oxidase (AlOx), respectively and showing very good results in comparison with the biosensors of the Literature, with limit of detections of 2 ppm for glucose and 1 ppm for ethanol. Moreover, the influence of oxygen was studied, obtaining better results in its presence for glucose detection and in its absence for ethanol determination, probably due to the aerobic or anaerobic character of the enzyme bacterium. Proton conducting polymers show a cation/proton conductivity along the polymer backbone thanks to the presence of carboxylated or sulfonated groups with a cationic counter ion, whose mobility can be increased by water swelling. For this peculiarity, they present low electrical resistance (obtained increasing ion exchange capacity and water content and decreasing membrane thickness), high permeoselectivity for anions and non-ionized molecules, good mechanical and chemical stability over long periods. Their properties depend on many factors, such as the chemical nature of the polymer backbone, the polymer molecular weight and molecular weight distribution, the nature of the solvent used for casting and the possible presence of residual solvent in the polymeric film. Poly(aryl ether sulfone) (PES) was studied as a new material for the production of modified electrodes in comparison with Nafion. For its characterization, different parameters have been studied: the quantity and the form of the polymer, its storage, its method of drying and the casting solvent. In particular, 1 % linear PES in the acidic form, dried at 25 \ub0C in oven, dissolved in N-Methylpyrrolidone, showed the best performance, superior to Nafion. These polymers presented a very interesting behaviour, since without the redox probe, capacitance was comparable to glassy carbon, while when the redox probe was present, capacitance increased of two orders of magnitude and diffusion of the probe changed, probably due to variation of diffusion mechanism in the polymeric structure. Future developments will consider the applications of these new interesting systems for the detection of various important analytes or pollutants. Furthermore, new types of sensors and biosensors based on different types of the advanced materials studied and their combination will be considered. [1] D.T. Pierce, J.X. Zhao, Trace Analysis with Nanomaterials, Wiley-VCH, Weinheim (Germany), (2010) [2] J. Zima, I. Svancara, J. Barek, K. Vytras, Crit. Rev. Anal. Chem. 2009, 39, 204-227

Studying the evolution in time of bimetallic nanoparticles morphology by Cyclic Voltammetry

Over the last decades, bimetallic nanosized systems have attracted more and more interest thanks to their novel optical, catalytic, magnetic, and sensing properties, often different from the ones of their monometallic counterparts. Studies directed towards the size, shape, composition, and functionalization of the bimetallic nanoparticles are optimized to design sophisticated materials for the intended applications. Considering these facts, it is important to evaluate not only the type and the quantity of the two metals involved, but also their morphological distribution (e.g. alloy or core-shell). Characterization techniques normally used to investigate bimetallic systems are HR-TEM and EXAFS, very expensive and not so easily accessible. Recently, electrochemistry has been employed as alternative or complementary, low-cost, efficient technique with very promising results, allowing the discrimination between alloyed and perfect or defective core-shell systems after their synthesis. A further achievement is the possibility to follow step by step the formation morphology of these nanomaterials during their synthetic procedure. In the present work, we present a study on Au-Pt bimetallic nanoparticles, in form of alloy or core-shell. Cyclovoltammetry (CV) is used as a fast, low-cost and simple screening technique to distinguish the general composition of the sample and to understand the evolution in time of the systems morphology during their synthesis. An additional advantage is the possibility to conduct the study of the material simply in liquid form, without the need of using solid supports, as normally required by other characterization techniques. Interesting results are obtained for Au-based bimetallic samples, gaining information in accordance with TEM images and EXAFS spectra. This fact moves the interest towards the study of other bimetallic systems, to be used in catalytic, electrocatalytic and electroanalytical applications

A Concerted Electrochemical and Theoretical Investigation of the Ag/TiO2 nano-heterojunction

Suitably designed nano-heterojunctions are able to enhance synergistic functionalities of different materials yielding to \u201cbrave new systems\u201d with innovative and sometimes unexpected physicochemical properties [1]. However, the complete understanding of these devices has to be deeply studied. In this work, a concerted theoretical and electrochemical investigation is proposed to gain insights into a metal-semiconductor interface, namely that created by the silver/anatase hybrid nanocomposite, a promising material for advanced sensing applications [2]. In particular, it provided the first photorenewable and anti-fouling sensor device, enhancing the analytical limits in terms of accuracy, sensitivity, detection limits, and photoactivity [3]. Furthermore, the hybrid material is proven to be extremely robust against aging, showing complete regeneration, also after one-year storage. The electrochemical/electroanalytical virtues of the Ag/TiO2 junction were evaluated in terms of current densities and reproducibility, providing their explanation at the atomic-scale level and demonstrating how and why the final device can act as silver-cation positive electrode [4]. Moreover, Cyclic Voltammetry and Electrochemical Impedance Spectroscopy were used in combination with periodic plane-wave DFT calculations, giving comparable qualitative but also quantitative results. In particular, we theoretically estimated the overall amount of electron transfer toward the semiconductor side of the interface at equilibrium and suitably designed electrochemical experiments, which strictly agree with the theoretical charge transfer estimates. Moreover, photoelectrochemical measurements and theoretical predictions show the unique permanent charge separation occurring in the device [4]. [1] A.V. Emeline, V.N. Kuznetsov, V.K. Ryabchuk, N. Serpone, Environ. Sci. Pollut. Res., 2012, 19, 3666\u20133675. [2] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst, 2015, 140, 1486\u20131494. [3] V. Pifferi, G. Soliveri, G. Panzarasa, G. Cappelletti, D. Meroni, L. Falciola, Anal. Bioanal. Chem., 2016, 408, 7339\u20137349. [4] G. Di Liberto, V. Pifferi, L. Lo Presti, M. Ceotto, L. Falciola, J. Phys. Chem. Lett., 2017, 8, 5372\u20135377

Mesoporous silica networks with improved diffusion and interference-rejecting properties for electroanalytical sensing

Mesoporous silica materials characterized by well-ordered microstructure and size- and shape-controlled pores have attracted much attention in the last years. These systems can be used for the development of functional thin films for advanced applications in catalysis and electrocatalysis, sensors and actuators, separation techniques, micro- and nano-electronic engineering [1-2]. In this work, \u201cinsulating\u201d and mesoporous silica films were prepared by spin coating a home-made silica sol on a cleaned ITO glass support. The mesoporosity was controlled by the use of Polystyrene (PS) latex beads with different dimensions (30-60-100 nm) as template. The number of successive multi-layer depositions was varied (1-2-3-5 layers) and after the template removal, stable, homogeneous and reproducible transparent films were obtained, characterized by an interconnected porous structure. The morphological features and the physicochemical and optical properties of the films and/or sol-precursors were studied by DLS, FE-SEM, AFM, UV-vis transmittance spectroscopy and wettability analyses. Moreover, a deep electrochemical characterization was also performed by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). In particular, the use of two redox mediator probes [(K4Fe(CN)6) and (Ru(NH3)6Cl3)], presenting opposite charge and different diffusional behaviour, allowed the comprehension of the mass transport and charge transfer phenomena, evidencing the effects of spatial confinement and charge selection. In the case of \u201cinsulating\u201d films prepared without the use of PS latexes, we proved an experimental evidence for theoretical models [3] concerning electroinactive layer-modified electrodes, with a scan-rate-dependent variation of the CV shape due to a progressive increase in the diffusion coefficient inside the insulating layer. A complex balance between diverging effects (higher hydrophilicity and insulating behavior effects of silica) when increasing the numbers of layers was also observed [4]. In the case of mesoporous layers, a better electrochemical response of smaller pores and of thicker layers was found, due to two main cooperative phenomena: i) a diffusion modification from fully planar to radial-convergent at the pore-silica interface due to surface porosity; ii) the presence of pores in a hydrophilic matrix which leads to a capillary pull effects, stronger in the case of smaller hydrophilic pores. The easiness of preparation and the interesting properties of these devices pave the way towards their use in many fields, particularly trace electroanalysis in real matrices. In fact, for example, the porous and properly charged network is able to exclude interfering macromolecules (mucin in our case), preventing electrode biofouling and enhancing the performances of the sensor towards dopamine detection. References [1] M. Ogawa, Chem. Rec. 17 (2017) 217-232. [2] A. Walcarius, Chem. Soc. Rev. 42 (2013) 4098-4140. [3] D. Menshykau, R.G. Compton, Langmuir 25 (2009) 2519\u20132529. [4] V. Pifferi, L. Rimoldi, D. Meroni, F. Segrado, G. Soliveri, S. Ardizzone, L. Falciola, Electrochem. Commun. 81 (2017) 102-105

A Concerted Investigation For Metal/Semiconductor Nanointerface : Interlayer Charge Transfer At Ag/TiO2

In the field of hybrid materials, suitably designed nanoheterojunctions enhance synergistic functionalities and allow to obtain \u201cbrave new materials\u201d with physicochemical properties that are not simply the addition of the precursors\u2019 ones, but are completely new, different, and sometimes unexpected. For these reasons, the use of them has paved the way toward promising applications in many fields, such as electrocatalysis, photocatalysis, electroanalysis, and environmental chemistry, impacting on the everyday life [1]. However, research on such systems is most often dominated by trial and error procedures, while a deep atomistic understanding of the phenomena inside the junction region driving appropriate design of the final device is missing. Here, a concerted theoretical and electrochemical investigation is proposed to gain insights into the important class of heterojunctions made by metal-semiconductor interfaces. The presented case of study is the silver/anatase hybrid nanocomposite, a very promising material for advanced sensing applications [2]. Considering that in most cases titania semiconductors are useless in electroanalysis and silver is subject to fouling and oxidation/passivation, such broad outcomes were totally unexpected. Specifically, Ag/TiO2 interfase provided the first photorenewable sensor device, pushing the limits in terms of accuracy, sensitivity, detection limits, and photoactivity [3]. Despite the ongoing research, a quantitative and comprehensive understanding of the physics behind this nanocomposite is still missing, thus preventing its full exploitation and the extension of the same paradigm to other systems and devices. In particular, cyclic voltammetry and electrochemical impedance spectroscopy are used in combination with periodic plane-wave DFT calculations, giving comparable qualitative, but also quantitative results. We measure the exceptional electrochemical virtues of the Ag/TiO2 junction in terms of current densities and reproducibility, providing their explanation at the atomic-scale level and demonstrating how and why silver acts as a positive electrode [4]. We theoretically estimate the overall amount of electron transfer toward the semiconductor side of the interface at equilibrium and suitably designed electrochemical experiments strictly agree with the theoretical charge transfer estimates. Moreover, photoelectrochemical measurements and theoretical predictions show the unique permanent charge separation occurring in the device, possible because of the synergy of Ag and TiO2, which exploits in a favorable band alignment, in a smaller electron\u2013hole recombination rate and in a reduced carrier mobility when electrons cross the metal\u2013semiconductor interface. Finally, the hybrid material is proven to be extremely robust against aging, showing complete regeneration, even after one year [4]. [1] A.V. Emeline, V.N. Kuznetsov, V.K. Ryabchuk, N. Serpone, Environ. Sci. Pollut. Res. 19 (2012) 3666\u20133675. [2] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst 140 (2015) 1486\u20131494. [3] V. Pifferi, G. Soliveri, G. Panzarasa, G. Cappelletti, D. Meroni, L. Falciola, Anal. Bioanal. Chem. 408 (2016) 7339\u20137349. [4] G. Di Liberto, V. Pifferi, L. Lo Presti, M. Ceotto, and L. Falciola, J. Phys. Chem. Lett. 8 (2017) 5372\u20135377

Antibiotic Prophylaxis to Reduce Respiratory Tract Infections and Mortality in Adults Receiving Intensive Care

BACKGROUND: Pneumonia is an important cause of mortality in intensive care units (ICUs). The incidence of pneumonia in ICU patients ranges between 7% and 40%, and the crude mortality from ventilator-associated pneumonia may exceed 50%. Although not all deaths in patients with this form of pneumonia are directly attributable to pneumonia, it has been shown to contribute to mortality in ICUs independently of other factors that are also strongly associated with such deaths. OBJECTIVES: To assess the effects of prophylactic antibiotic regimens, such as selective decontamination of the digestive tract (SDD) for the prevention of respiratory tract infections (RTIs) and overall mortality in adults receiving intensive care. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2009, issue 1), which contains the Cochrane Acute Respiratory Infections (ARI) Group's Specialised Register; MEDLINE (January 1966 to March 2009); and EMBASE (January 1990 to March 2009). SELECTION CRITERIA: Randomised controlled trials (RCTs) of antibiotic prophylaxis for RTIs and deaths among adult ICU patients. DATA COLLECTION AND ANALYSIS: At least two review authors independently extracted data and assessed trial quality. MAIN RESULTS: We included 36 trials involving 6914 people. There was variation in the antibiotics used, patient characteristics and risk of RTIs and mortality in the control groups. In trials comparing a combination of topical and systemic antibiotics, there was a significant reduction in both RTIs (number of studies = 16, odds ratio (OR) 0.28, 95% confidence interval (CI) 0.20 to 0.38) and total mortality (number of studies = 17, OR 0.75, 95% CI 0.65 to 0.87) in the treated group. In trials comparing topical antimicrobials alone (or comparing topical plus systemic versus systemic alone) there was a significant reduction in RTIs (number of studies = 17, OR 0.44, 95% CI 0.31 to 0.63) but not in total mortality (number of studies = 19, OR 0.97, 95% CI 0.82 to 1.16) in the treated group. AUTHORS' CONCLUSIONS: A combination of topical and systemic prophylactic antibiotics reduces RTIs and overall mortality in adult patients receiving intensive care. Treatment based on the use of topical prophylaxis alone reduces respiratory infections but not mortality. The risk of resistance occurring as a negative consequence of antibiotic use was appropriately explored only in one trial which did not show any such effect

Graphene Oxide-Based Hybrids for Chemiresistive VOCs Sensors

INTRODUCTION The sensing of gas molecules is of primary importance for environmental monitoring, control of chemical processes, medical applications, and so on1. In recent years, graphene-based gas sensors have attracted much attention due to enhanced graphene thermo-electric conductivity, surface area and mechanical strength. Thus, different structures have been developed and high sensing performances and room temperature working conditions were achieved1. However, they still suffer from several problems, which could be overcome by covering the graphene surface with metal oxide nanoparticles2. Furthermore, studies regarding the detection of Volatile Organic Compounds (VOCs) are still at the beginning1. Hence, the present work will be aimed at: i) optimizing the synthetic routes of ad hoc composite VOCs sensing materials (based on graphene oxide/SnO2 or ZnO hybrids) and their deep physico-chemical characterizations; ii) engineering the gas sensor device; and iii) evaluating the sensing performances at both high and mild temperatures (also exploiting the UV light) towards gaseous ethanol, acetone and ethylbenzene. EXPERIMENTAL/THEORETICAL STUDY Starting from pure graphite, graphene oxide (GO) powder was synthesized by adopting the Hummer\u2019s modified method2. The synthetic route was deeply investigated by modulating both the starting carbon material (powder or flakes graphite) and the concentration of the H2O2 (i.e. the quenching/oxidizing agent), thus tailoring the final GO surface/structural properties. Once optimized this step, SnO2 or ZnO were grown on its surface by a hydrothermal method, varying the starting salt precursor/GO weight ratio (ZnxGO or SnxGO, x = 4, 8, 16, 32). For comparison, pure SnO2 and ZnO (both commercial and home-made) were also tested. Several physico-chemical techniques have been used to characterize all the as-prepared nanopowders, such as XRPD, BET, Raman, FTIR, XPS, TEM and electrochemical analyses (CV and EIS). Subsequently, a homogeneous layer was deposited by spraying technique onto Pt-Interdigitated Electrodes (IDEs) starting from an ethanol suspension of each sample (2.5 mg mL-1). Then, gaseous ethanol, acetone and ethylbenzene (the more interesting one, being nowadays the less studied VOC) were sensed by using a Linkam Scientific stage, equipped with an electrochemical workstation for the chronoamperometric measurements. RESULTS AND DISCUSSION The effective synthesis of graphene oxide sheets and, subsequently, the growth of metal oxide nanoparticles on its surface were confirmed by exploiting different physico-chemical techniques. As concerns the VOCs sensing analyses, we obtained very promising results (in terms of both response/recovery time and sensibility down to ppb levels) for either pure and hybrid materials at 350\ub0C, and at lower temperatures (150\ub0C to RT, by exploiting UV light) for the graphene-based samples (Figure 1), thanks to the presence of the carbon material.Furthermore, a similar behavior has been noticed towards acetone and ethylbenzene pollutants. CONCLUSION Very promising results have been obtained with graphene oxide-based materials, which reveal to be more performing than the corresponding pure samples. Hence, these powders may represent very potential candidates for the gas sensing of highly toxic VOCs traces, both for environmental and medical diagnosis1 purposes

Interactions between permeation and gating in the TMEM16B/anoctamin2 calcium-activated chloride channel

At least two members of the TMEM16/anoctamin family, TMEM16A (also known as anoctamin1) and TMEM16B (also known as anoctamin2), encode Ca2+-activated Cl- channels (CaCCs), which are found in various cell types and mediate numerous physiological functions. Here, we used whole-cell and excised inside-out patch-clamp to investigate the relationship between anion permeation and gating, two processes typically viewed as independent, in TMEM16B expressed in HEK 293T cells. The permeability ratio sequence determined by substituting Cl- with other anions (PX/PCl) was SCN- > I- > NO3- > Br- > Cl- > F- > gluconate. When external Cl- was substituted with other anions, TMEM16B activation and deactivation kinetics at 0.5 μM Ca2+ were modified according to the sequence of permeability ratios, with anions more permeant than Cl- slowing both activation and deactivation and anions less permeant than Cl- accelerating them. Moreover, replacement of external Cl- with gluconate, or sucrose, shifted the voltage dependence of steady-state activation (G-V relation) to more positive potentials, whereas substitution of extracellular or intracellular Cl- with SCN- shifted G-V to more negative potentials. Dose-response relationships for Ca2+ in the presence of different extracellular anions indicated that the apparent affinity for Ca2+ at +100 mV increased with increasing permeability ratio. The apparent affinity for Ca2+ in the presence of intracellular SCN- also increased compared with that in Cl-. Our results provide the first evidence that TMEM16B gating is modulated by permeant anions and provide the basis for future studies aimed at identifying the molecular determinants of TMEM16B ion selectivity and gating. © 2014 Betto et al

Au Nanoparticles Decorated Graphene-Based Hybrid Nanocomposite for As(III) Electroanalytical Detection

Electrochemical sensors integrating hybrid nanostructured platforms are a promising alternative to conventional detection techniques for addressing highly relevant challenges of heavy metal determination in the environment. Hybrid nanocomposites based on graphene derivatives and inorganic nanoparticles (NPs) are ideal candidates as active materials for detecting heavy metals, as they merge the relevant physico-chemical properties of both the components, finally leading to a rapid and sensitive current response. In this work, a hybrid nanocomposite formed of reduced graphene oxide (RGO) sheets, surface functionalized by π-π interactions with 1-pyrene carboxylic acid (PCA), and decorated in situ by Au NPs, was synthesized by using a colloidal route. The hybrid nanocomposite was characterized by cyclic voltammetry and electrochemical impedance spectroscopy with respect to the corresponding single components, both bare and deposited as a layer-by-layer junction onto the electrode. The results demonstrated the high electrochemical activity of the hybrid nanocomposite with respect to the single components, highlighting the crucial role of the nanostructured surface morphology of the electrode and the PCA coupling agent at the NPs-RGO interphase in enhancing the nanocomposite electroactivity. Finally, the Au NP-decorated PCA-RGO sheets were tested by anodic stripping voltammetry of As(III) ion—a particularly relevant analyte among heavy metal ions—in order to assess the sensing ability of the nanocomposite material with respect to its single components. The nanocomposite has been found to present a sensitivity higher than that characterizing the bare components, with LODs complying with the directives established by the U.S. EPA and in line with those reported for state-of-the-art electrochemical sensors based on other Au-graphene nanocomposites