Gas sensing at the nanoscale: engineering SWCNT-ITO nano-heterojunctions for the selective detection of NH3 and NO2 target molecules.

The gas response of single-wall carbon nanotubes (SWCNT) functionalized with indium tin oxide (ITO) nanoparticles (NP) has been studied at room temperature and an enhanced sensitivity to ammonia and nitrogen dioxide is demonstrated. The higher sensitivity in the functionalized sample is related to the creation of nano-heterojunctions at the interface between SWCNT bundles and ITO NP. Furthermore, the different response of the two devices upon NO2 exposure provides a way to enhance also the selectivity. This behavior is rationalized by considering a gas sensing mechanism based on the build-up of space-charge layers at the junctions. Finally, full recovery of the signal after exposure to NO2 is achieved by UV irradiation for the functionalized sample, where the ITO NP can play a role to hinder the poisoning effects on SWCNT due to NO2 chemisorption.

Humidity-enhanced sub-ppm sensitivity to ammonia of covalently functionalized single-wall carbon nanotube bundle layers.

A low-cost method for carbon nanotubes (CNTs) network production from solutions on flexible polyethylene naphthalate substrates has been adopted to prepare high quality and well characterized SWCNT bundle layers to be used as the active layer in chemiresistor gas sensors. Two types of SWCNTs have been tested: pristine SWCNTs, deposited from a surfactant solution, and covalently functionalized SWCNTs, deposited from a dimethyl-acetamide solution. The humidity effects on the sensitivity of the SWCNTs network to NH3 have been investigated. The results show that relative humidity favors the response to NH3, confirming recent theoretical predictions. The COOH-functionalized sample displays the largest response owing to both its hydrophilic nature, favoring the interaction with H2O molecules, and its largest surface area. Compared to data available in the literature, the present sensors display a remarkable sensitivity well below the ppm range, which makes them quite promising for environmental and medical applications, where NH3 concentrations (mostly of the order of tens of ppb) have to be detected.

Transfer of CVD-grown graphene for room temperature gas sensors.

An easy transfer procedure to obtain graphene-based gas sensing devices operating at room temperature (RT) is presented. Starting from chemical vapor deposition-grown graphene on copper foil, we obtained single layer graphene which could be transferred onto arbitrary substrates. In particular, we placed single layer graphene on top of a SiO2/Si substrate with pre-patterned Pt electrodes to realize a chemiresistor gas sensor able to operate at RT. The responses to ammonia (10, 20, 30 ppm) and nitrogen dioxide (1, 2, 3 ppm) are shown at different values of relative humidity, in dark and under 254 nm UV light. In order to check the sensor selectivity, gas response has also been tested towards hydrogen, ethanol, acetone and carbon oxide. Finally, a model based on linear dispersion relation characteristic of graphene, which take into account humidity and UV light effects, has been proposed.

How reliable is assessment of true vocal cord-arytenoid unit mobility in patients affected by laryngeal cancer? a multi-institutional study on 366 patients from the ARYFIX collaborative group.

PURPOSE: In clinical practice the assessment of the "vocal cord-arytenoid unit" (VCAU) mobility is crucial in the staging, prognosis, and choice of treatment of laryngeal squamous cell carcinoma (LSCC). The aim of the present study was to measure repeatability and reliability of clinical assessment of VCAU mobility and radiologic analysis of posterior laryngeal extension. METHODS: In this multi-institutional retrospective study, patients with LSCC-induced impairment of VCAU mobility who received curative treatment were included; pre-treatment endoscopy and contrast-enhanced imaging were collected and evaluated by raters. According to their evaluations, concordance, number of assigned categories, and inter- and intra-rater agreement were calculated. RESULTS: Twenty-two otorhinolaryngologists evaluated 366 videolaryngoscopies (total evaluations: 2170) and 6 radiologists evaluated 237 imaging studies (total evaluations: 477). The concordance of clinical rating was excellent in only 22.7% of cases. Overall, inter- and intra-rater agreement was weak. Supraglottic cancers and transoral endoscopy were associated with the lowest inter-observer reliability values. Radiologic inter-rater agreement was low and did not vary with imaging technique. Intra-rater reliability of radiologic evaluation was optimal. CONCLUSIONS: The current methods to assess VCAU mobility and posterior extension of LSCC are flawed by weak inter-observer agreement and reliability. Radiologic evaluation was characterized by very high intra-rater agreement, but weak inter-observer reliability. The relevance of VCAU mobility assessment in laryngeal oncology should be re-weighted. Patients affected by LSCC requiring imaging should be referred to dedicated radiologists with experience in head and neck oncology.

Structural changes and lateral redistribution of photosystem II during donor side photoinhibition of thylakoids.

The structural and topological stability of thylakoid components under photoinhibitory conditions (4,500 microE.m-2.s-1 white light) was studied on Mn depleted thylakoids isolated from spinach leaves. After various exposures to photoinhibitory light, the chlorophyll-protein complexes of both photosystems I and II were separated by sucrose gradient centrifugation and analysed by Western blotting, using a set of polyclonals raised against various apoproteins of the photosynthetic apparatus. A series of events occurring during donor side photoinhibition are described for photosystem II, including: (a) lowering of the oligomerization state of the photosystem II core; (b) cleavage of 32-kD protein D1 at specific sites; (c) dissociation of chlorophyll-protein CP43 from the photosystem II core; and (d) migration of damaged photosystem II components from the grana to the stroma lamellae. A tentative scheme for the succession of these events is illustrated. Some effects of photoinhibition on photosystem I are also reported involving dissociation of antenna chlorophyll-proteins LHCI from the photosystem I reaction center.

Improved recovery time and sensitivity to H2 and NH3 at room temperature with SnOx vertical nanopillars on ITO.

Nanostructured SnO2 is a promising material for the scalable production of portable gas sensors. To fully exploit their potential, these gas sensors need a faster recovery rate and higher sensitivity at room temperature than the current state of the art. Here we demonstrate a chemiresistive gas sensor based on vertical SnOx nanopillars, capable of sensing < 5 ppm of H2 at room temperature and 10 ppt at 230 °C. We test the sample both in vacuum and in air and observe an exceptional improvement in the performance compared to commercially available gas sensors. In particular, the recovery time for sensing NH3 at room temperature is more than one order of magnitude faster than a commercial SnO2 sensor. The sensor shows an unique combination of high sensitivity and fast recovery time, matching the requirements on materials expected to foster widespread use of portable and affordable gas sensors.

A cross-functional nanostructured platform based on carbon nanotube-Si hybrid junctions: where photon harvesting meets gas sensing.

A combination of the functionalities of carbon nanotube (CNT)-Si hybrid heterojunctions is presented as a novel method to steer the efficiency of the photovoltaic (PV) cell based on these junctions, and to increase the selectivity and sensitivity of the chemiresistor gas sensor operated with the p-doped CNT layer. The electrical characteristics of the junctions have been tracked by exposing the devices to oxidizing (NO2) and reducing (NH3) molecules. It is shown that when used as PV cells, the cell efficiency can be reversibly steered by gas adsorption, providing a tool to selectively dope the p-type layer through molecular adsorption. Tracking of the current-voltage curve upon gas exposure also allowed to use these cells as gas sensors with an enhanced sensitivity as compared to that provided by a readout of the electrical signal from the CNT layer alone. In turn, the chemiresistive response was improved, both in terms of selectivity and sensitivity, by operating the system under illumination, as the photo-induced charges at the junction increase the p-doping of CNTs making them more sensitive to NH3 and less to NO2.

Submitochondrial localization and partial purification of the succinylCoA: 3-hydroxy-3-methylglutarate coenzyme A transferase from rat liver.

The presence and the localization of the enzyme catalyzing the transfer of a coenzyme A molecule from succinyl-CoA to 3-hydroxy-3-methylglutarate has been established in rat liver mitochondria. The enzyme was found mainly in the mitochondrial matrix but some activity was also found in the inner membrane fraction. The enzyme has been purified about 100-fold from sonically-disrupted mitochondria by high-speed centrifugation, DEAE-cellulose chromatography, (NH4)2SO4 precipitation and Sephadex G-100 filtration. The enzymatic activity was recovered in the final step as a single peak. The coenzyme A transferase appears to have a molecular weight of 42 000, the highest activity at pH 8.5 and an energy of activation of 13 kcal/mol. Mercaptoethanol increases the activity and improves its stability. The enzyme is different from the succinylCoA: 3-oxoacids coenzyme A transferase and is active also on malonylCoA. The apparent Km values obtained for succinylCoA, malnylCoA and 3-hydroxy-3-methylglutarate were 2.2 . 10(-4) M, 3.7 . 10(-4) M and 1.7 . 10(-3) M, respectively. Acetoacetate, which is the final product of the mitochondrial metabolism of hydroxy-methylglutarylCoA, showed an inhibitory effect on the enzyme activity with a Ki of 0.5 mM. The physiological role of the enzyme is discussed.

Effects of calcium chelators, divalent cations and sulfhydryl reagents on calcium uptake and motility of bovine spermatozoa.

Addition of 1 mM Ca/EGTA complex (1:1 ratio) to an incubation medium containing 1.5 mM Ca2+ produced a notable increase in the Ca2+ cycling in ejaculated bovine spermatozoa. Similar results were also obtained with the Ca/EDTA and Ca/EDTA complexes or with the heavy metal chelator DTPA (50 microM). Ba2+, Ni2+ or Co2+ added at 0.1 mM concentration abolished the stimulatory effect of the Ca/EGTA complex on Ca2+ cycling, whereas it did not affect the calcium movement in the absence of the calcium chelator complex. It is concluded that small amounts of these cations should be bound to the plasma membrane of bovine spermatozoa and inhibit the cellular calcium influx. 0.1 mM Cd2+ and NEM or 1 mM diamide produced a calcium efflux from the spermatozoa together with an inhibition of cellular motility and an increase in glutamate-oxaloacetate transaminase release. Conversely the impermeant sulfhydryl reagent mersalyl caused a net calcium efflux but did not alter the cellular motility nor the transaminase release. It is suggested that the permeant thiol reagents could decrease the spermatozoal mobility by impairing the mitochondrial ATP-synthesis.

Ruthenium red inhibits the mitochondrial Ca2+ uptake in intact bovine spermatozoa and increases the cytosolic Ca2+ concentration.

The uptake and cycling of Ca2+ by ejaculated bovine spermatozoa are almost completely abolished by ruthenium red, antimycin A or FCCP. The inhibitory effect of ruthenium red is also observed after washing of the dye-pretreated cells followed by addition of digitonin or filipin. In contrast, the inhibition is overcome by A23187 treatment. It is concluded that ruthenium red penetrates into intact spermatozoa, inhibits the mitochondrial Ca2+ uptake 'in situ', and causes the observed increase of the cytosolic free Ca2+ concentration.

Characterization of a 41 kDa photoinhibition adduct in isolated photosystem II reaction centres.

When isolated reaction centres of photosystem II are subjected to photoinhibitory illumination, a 41 kDa SDS-PAGE band is observed under all experimental conditions. The same band is also found, together with lower molecular weight fragments of the D1 protein, in whole thylakoids and in all PSII sub-particles investigated up to now. In the case of isolated reaction centres the 41 kDa band is represented by a heterodimer of the D1 polypeptide and the alpha-subunit of cytochrome b559. The cross-linkage between D1 and alpha-cyt b559 involves a region on D1 between the N-terminal residue and Arg-225, and is an early event in photo-induced damage to the D1 protein.

Photoinduced degradation of the D1 protein in isolated thylakoids and various photosystem II particles after donor-side inactivations. Detection of a C-terminal 16 kDa fragment.

Photoinduced degradation of the photosystem II (PSII) reaction center D1 protein was studied in isolated thylakoids and different PSII subparticles. A 16 kDa fragment corresponding to the C-terminus of the protein is detected in thylakoids when they are inactivated at the donor side before illumination. The same D1 fragment is found in different types of PSII preparations at different integration levels characterized by different polypeptide compositions so long as they have an inactivated donor side and an active electron acceptor for the reduced pheophytin. However, when the PSII particle is equal to or smaller than the 43-less PSII core complex, other fragments are observed which are not found in more integrated systems.

Light-induced degradation of D2 protein in isolated photosystem II reaction center complex.

When isolated photosystem II reaction centers from spinach are exposed to photoinhibitory light in the presence of an electron acceptor, breakdown products of the D2 protein at 28, 25, 23, 18, 9, 5 and 4.5 kDa are detected by immunoblotting with a monospecific anti-D2 polyclonal antibody. In a time-course experiment the 23 and 4.5 kDa fragments show a transient appearance, whilst the others are photoaccumulated. The regions of the D2 protein containing the cleavage sites for the 28 and 18 kDa photoinduced fragments have been identified. Significant degradation of D2 takes place only in the presence of an electron acceptor, and breakdown of the protein is partially prevented by serine-type protease inhibitors.

Cytochrome b6/f complex from the cyanobacterium Synechocystis 6803: evidence of dimeric organization and identification of chlorophyll-binding subunit.

Fractionation of photosynthetic membranes from the cyanobacterium Synechocystis 6803 by polyacrylamide gel electrophoresis in the presence of Deriphat-160 allowed the isolation of a number of pigmented bands. Two of them, with molecular masses of 240+/-20 and 110+/-15 kDa respectively, showed peroxidase activity and, by means of polypeptide composition, immunoblotting and N-terminal sequencing, were identified as dimeric and monomeric cytochrome b6/f complexes, containing 1.3+/-0.35 chlorophyll molecules per cytochrome f. Further fractionation of monomeric complexes by mild gel electrophoresis in the presence of sodium dodecyl sulfate indicated that it is the cytochrome b6 polypeptide which provides the actual binding site for the chlorophyll molecule observed in the complex.

Imagery deficits in nonverbal learning disabilities.

This study reports the observations gathered from 11 children referred to consulting services because of learning difficulties at school and diagnosed with nonverbal learning disabilities (NVLD). These children had an average verbal IQ, but a WISC-R performance IQ lower than the verbal IQ by at least 15 points and experienced difficulties especially in mathematics and drawing. The children completed a battery of four tasks requiring visuospatial working memory and visual imagery: a memory task composed of pictures and their positions (Pictures task), a task that required them to memorize the positions filled in a matrix (Passive Matrix task), a task that required them to imagine a pathway along a matrix (Active Matrix task) and a task that required them to learn groups made up of three words, using a visual interactive imagery strategy (TV task). In comparison to a control group of 49 children, children with NVLD scored lower in all the tasks, showing deficits in the use of visuospatial working memory and visual imagery. By contrasting subgroups of children of different ages in the control group, it was possible to show that some tasks did not show a clear developmental trend. Thus the deficits shown by the children with NVLD cannot simply be attributed to a developmental delay of these children, but seem to reflect a more severe disability.

Calcium efflux parallel to total phosphate retention in rat liver mitochondria.

Phosphate efflux from uncoupled rat liver mitochondria was completely inhibited when mersalyl plus butylmalonate and ATP were added to a sucrose suspending medium. Despite the total retention of phosphate a calcium efflux was observed even in presence of ruthenium red. Under the above conditions no phosphate is transported in association with the ADP/ATP carrier. While mersalyl completely blocked the phosphate release induced by ruthenium red or EGTA from coupled mitochondria it only partially inhibited the CA2+-efflux. The inhibition of Ca2+ efflux was almost completely abolished in the presence of acetate. The existence of a co-transport of Ca2+ associated with phosphate is discussed.

Inhibition of rat liver mitochondrial 3-hydroxy-3-methylglutaryl-CoA lyase by succinyl-CoA.

1. Succinyl-CoA inhibits 3-hydroxy-3-methyl-glutaryl-CoA lyase (EC 4.1.3.4) when added to purified preparations of the enzyme. 2. The apparent Ki value is 2.1 x 10(-4) mol/l and the inhibition has the features of a partially competitive inhibition. 3. The effect of succinyl-CoA both added and enzymically produced on the lyase activity of sonically disrupted rat liver mitochondria results in decreased acetoacetate formation. 4. This occurs with mitochondria obtained from normal, starved and streptozotocin-diabetic rats.

Formation and utilization of 3-hydroxy-3-methylglutarate in liver mitochondria of starved and streptozotocin-diabetic rats.

Kidney and liver mitochondria of rat, rabbit and guinea pig are able to transform 3-hydroxy-3-methylglutarate into acetoacetate, whereas ox liver mitochondria and rat mitochondria of heart, diaphragm and brain do not exhibit such an activity. Starvation and streptozotocin treatment decreases the formation of acetoacetate from 3-hydroxy-3-methylglutarate. Addition of acetoacetate and succinate to the incubation media of mitochondria results in a decrease in the transformation of 3-hydroxy-3-methylglutarate into acetoacetate. A 3-hydroxy-3-methylglutaryl-CoA hydrolase is present in rat liver mitochondria; the activity does not show appreciable changes after starvation or streptozotocin treatment.