General Purpose Transistor Characterized as Dosimetry Sensor of Proton Beams.

A commercial pMOS transistor (MOSFET), 3N163 from Vishay (USA), has been characterized as a low-energy proton beam dosimeter. The top of the samples' housing has been removed to guarantee that protons reached the sensitive area, that is, the silicon die. Irradiations took place at the National Accelerator Centre (Seville, Spain). During irradiations, the transistors were biased to improve the sensitivity, and the silicon temperature was monitored activating the parasitic diode of the MOSFET. Bias voltages of 0, 1, 5, and 10 V were applied to four sets of three transistors, obtaining an averaged sensitivity that was linearly dependent on this voltage. In addition, the short-fading effect was studied, and the uncertainty of this effect was obtained. The bias voltage that provided an acceptable sensitivity, (11.4 ± 0.9) mV/Gy, minimizing the uncertainty due to the fading effect (-0.09 ± 0.11) Gy was 1 V for a total absorbed dose of 40 Gy. Therefore, this off-the-shelf electronic device presents promising characteristics as a dosimeter sensor for proton beams.

Smart facemask for wireless CO2 monitoring.

The use of facemasks by the general population is recommended worldwide to prevent the spread of SARS-CoV-2. Despite the evidence in favour of facemasks to reduce community transmission, there is also agreement on the potential adverse effects of their prolonged usage, mainly caused by CO2 rebreathing. Herein we report the development of a sensing platform for gaseous CO2 real-time determination inside FFP2 facemasks. The system consists of an opto-chemical sensor combined with a flexible, battery-less, near-field-enabled tag with resolution and limit of detection of 103 and 140 ppm respectively, and sensor lifetime of 8 h, which is comparable with recommended FFP2 facemask usage times. We include a custom smartphone application for wireless powering, data processing, alert management, results displaying and sharing. Through performance tests during daily activity and exercise monitoring, we demonstrate its utility for non-invasive, wearable health assessment and its potential applicability for preclinical research and diagnostics.

Flexible Passive near Field Communication Tag for Multigas Sensing.

In this work we present a full-passive flexible multigas sensing tag for the determination of oxygen, carbon dioxide, ammonia, and relative humidity readable by a smartphone. This tag is based on near field communication (NFC) technology for energy harvesting and data transmission to a smartphone. The gas sensors show an optic response that is read through high-resolution digital color detectors. A white LED is used as the common optical excitation source for all the sensors. Only a reduced electronics with very low power consumption is required for the reading of the optical responses and data transmission to a remote user. An application for the Android operating system has been developed for the power supplying and data reception from the tag. The responses of the sensors have been calibrated and fitted to simple functions, allowing a fast prediction of the gases concentration. Cross-sensitivity has also been evaluated, finding that in most of the cases it is negligible or easily correctable using the rest of the readings. The election of the target gases has been due to their importance in the monitoring of modified atmosphere packaging. The resolutions and limits of detection measured are suitable for such kinds of applications.

An application of reconfigurable technologies for non-invasive fetal heart rate extraction.

This paper illustrates the use of a reconfigurable system for fetal electrocardiogram (FECG) estimation from mother's abdomen ECG measurements. The system is based on two different reconfigurable devices. Initially, a field-programmable analog array (FPAA) device implements the analog reconfigurable preprocessing for ECG signal acquisition. The signal processing chain continues onto a field-programmable gate array (FPGA) device, which contains all the communication and interfacing protocols along with specific digital signal processing blocks required for fundamental period extraction from FECG waveforms. The synergy between these devices provides the system the ability to change any necessary parameter during the acquisition process for enhancing the result. The use of a FPGA allows implementing different algorithms for FECG signal extraction, such as adaptive signal filtering. Preliminary works employ commercially available development platforms for test experiments, which suffice for the processing of real FECG signals from biomedical databases, as the presented results illustrate.

Thermal drift reduction with multiple bias current for MOSFET dosimeters.

New thermal compensation methods suitable for p-channel MOSFET (pMOS) dosimeters with the usual dose readout procedure based on a constant drain current are presented. Measuring the source-drain voltage shifts for two or three different drain currents and knowing the value of the zero-temperature coefficient drain current, I(ZTC), the thermal drift of source-drain or threshold voltages can be significantly reduced. Analytical expressions for the thermal compensation have been theoretically deduced on the basis of a linear dependence on temperature of the parameters involved. The proposed thermal modelling has been experimentally proven. These methods have been applied to a group of ten commercial pMOS transistors (3N163). The thermal coefficients of the source-drain voltage and the threshold voltage were reduced from -3.0 mV °C(-1), in the worst case, down to -70 µV °C(-1). This means a thermal drift of -2.4 mGy °C(-1) for the dosimeter. When analysing the thermal drifts of all the studied transistors, in the temperature range from 19 to 36 °C, uncertainty was obtained in the threshold voltage due to a thermal drift of ±9 mGy (2 SD), a commonly acceptable value in most radiotherapy treatments. The procedures described herein provide thermal drift reduction comparable to that of other technological or numerical strategies, but can be used in a very simple and low-cost dosimetry sensor.

Phosphorescent sensing of carbon dioxide based on secondary inner-filter quenching.

A study of different strategies to prepare phosphorescence-based sensors for gaseous CO(2) determination has been performed. It includes the characterization of different configurations tested, a discussion of the results obtained and possibilities for the future. The optical sensor for gaseous CO(2) is based on changes in the phosphorescence intensity of the platinum octaethylporphyrin (PtOEP) complex trapped both on oxygen-insensitive poly(vinylidene chloride-co-vinyl chloride) (PVCD) membranes and PVCD microparticles, due to the displacement of the alpha-naphtholphthalein acid-base equilibrium with CO(2) concentration. A secondary inner-filter mechanism was tested for the sensor and a full range linearized calibration was obtained by plotting (I(100)-I(0))/(I-I(0)) versus the inverse of the CO(2) concentration, where I(0) and I(100) are the detected luminescence intensities from a membrane exposed to 100% nitrogen and 100% CO(2), respectively, and I at a defined CO(2) concentration. The different configurations tested included the use of membranes containing luminophore and pH-sensitive dye placed on two opposite sides of a transparent support to prevent the observed degradation of the PtOEP complex in the presence of the tetraoctylammonium hydroxide (TOAOH) phase transfer agent, which produced better results regarding stability and sensitivity. The CO(2) gas sensor based on PtOEP homogeneous membranes presented better properties in terms of response time and sensitivity than that based on PtOEP microparticles. With a detection limit of 0.02%, the response time (10-90% maximum signal) is 9 s and the recovery time (90-10%) is 115 s. The lifetime of the membranes for CO(2) sensing preserved in a 94% RH atmosphere and dark conditions is longer than at least 4 months.

Monte Carlo simulation using the PENELOPE code with an ant colony algorithm to study MOSFET detectors.

In this work we have developed a simulation tool, based on the PENELOPE code, to study the response of MOSFET devices to irradiation with high-energy photons. The energy deposited in the extremely thin silicon dioxide layer has been calculated. To reduce the statistical uncertainties, an ant colony algorithm has been implemented to drive the application of splitting and Russian roulette as variance reduction techniques. In this way, the uncertainty has been reduced by a factor of approximately 5, while the efficiency is increased by a factor of above 20. As an application, we have studied the dependence of the response of the pMOS transistor 3N163, used as a dosimeter, with the incidence angle of the radiation for three common photons sources used in radiotherapy: a (60)Co Theratron-780 and the 6 and 18 MV beams produced by a Mevatron KDS LINAC. Experimental and simulated results have been obtained for gantry angles of 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees. The agreement obtained has permitted validation of the simulation tool. We have studied how to reduce the angular dependence of the MOSFET response by using an additional encapsulation made of brass in the case of the two LINAC qualities considered.

Portable light-emitting diode-based photometer with one-shot optochemical sensors for measurement in the field.

This report describes the electronics of a portable, low-cost, light-emitting diode (LED)-based photometer dedicated to one-shot optochemical sensors. Optical detection is made through a monolithic photodiode with an on-chip single-supply transimpedance amplifier that reduces some drawbacks such as leakage currents, interferences, and parasitic capacitances. The main instrument characteristics are its high light source stability and thermal correction. The former is obtained by means of the optical feedback from the LED polarization circuit, implementing a pseudo-two light beam scheme from a unique light source with a built-in beam splitter. The feedback loop has also been used to adjust the LED power in several ranges. Moreover, the low-thermal coefficient achieved (-90 ppm/degrees C) is compensated by thermal monitoring and calibration function compensation in the digital processing. The hand-held instrument directly gives the absorbance ratio used as the analytical parameter and the analyte concentration after programming the calibration function in the microcontroller. The application of this photometer for the determination of potassium and nitrate, using one-shot sensors with ionophore-based chemistries is also demonstrated, with a simple analytical methodology that shortens the analysis time, eliminating some calibrating solutions (HCl, NaOH, and buffer). Therefore, this compact instrument is suitable for real-time analyte determination and operation in the field.

Growth and exopolysaccharide (EPS) production by Oenococcus oeni I4 and structural characterization of their EPSs.

AIMS: To study the influence of medium constituents on growth, and exopolysaccharide (EPS) production by a strain of Oenococcus oeni. The structure of one of the EPSs has also been characterized. METHODS AND RESULTS: EPS concentration was estimated by the phenol/sulfuric acid method. After purification and fractionation of crude EPSs, the sugar composition was determined by GLC-MS of the TMS methyl glycosides. The major polysaccharide is 2-substituted-(1-3)-beta-D-glucan. This structure was determined by methylation analysis and conventional (1)H- and (13)C-nuclear magnetic resonance spectroscopy. In addition, O. oeni synthesized two heteropolysaccharides, although a lesser proportion, constituted by galactose and glucose, and one of them also showed rhamnose. The sugar source has a clear influence on growth and EPS synthesis, and EPS production was not enhanced by adding ethanol or increasing the nitrogen source. EPS biosynthesis starts in the exponential growth phase, and continued during the stationary growth phase. CONCLUSIONS: Higher EPS yields were obtained on cultures grown on glucose + fructose. O. oeni produces a beta-glucan, as the predominant EPS, and it is also able to produce two heteropolysaccharides. SIGNIFICANCE AND IMPACT OF THE STUDY: This work provides a better understanding of EPS synthesis by O. oeni and shows the first EPS structure described for this species.

A simplified measurement procedure and portable electronic photometer for disposable sensors based on ionophore-chromoionophore chemistry for potassium determination.

A field-portable photometer for potassium determination with disposable sensors has been developed. It can be applied to routine water and beverage analysis. The disposable sensor is based on ionophore-chromoionophore chemistry. A colour change in the sensing film is detected by measuring the transmitted intensity with a solid state photodetector. Optical excitation at 660 nm is emitted by a light-emitting diode (LED). Negative feedback for LED bias and thermal correction were included to improve system stability. Additionally, a measurement procedure is presented, characterized and validated for in situ photometer use and real-time results. This simplified procedure is based on prior preparation of the disposable sensor in its acidic form and on the use of an absorbance ratio as analytical parameter. The only requirement for analysis is prior equilibration with a buffered sample solution for 3 min and absorbance measurement before and after equilibration. Good sensitivity in the concentration range 5 muM to 100 mM and very good repetitively and stability were achieved that are comparable to those obtained with bulkier analytical instrumentation. Given the compact size, low weight, rapid response and low energy requirement of the electronic photometer developed here, this measurement system is suitable for potassium determination in the field.

A complex plant cell wall polysaccharide: rhamnogalacturonan II. A structure in quest of a function.

Walls of growing plants are extremely complex and sophisticated composite materials incorporating a dynamic assembly of polysaccharides, proteins and phenolics. Among the polysaccharides, the pectins encompass a group of acidic heteropolysaccharides; they offer a repertoire of structural complexity associated with the occurrence of, at least, three specific domains. Whereas most of these domains are notable for their structural heterogeneity, one of these, the so-called rhamnogalacturonan II (RG-II) exhibits a remarkable conservation throughout the plant kingdom. RG-II is thought to be the most complex plant polysaccharide on Earth (MW 5-10 kDa); its occurrence and strong conservation may indicate that it plays a major role in the structure and growth of higher plants. The present paper examines the most recent findings related to the occurrence, the structures, biosynthesis, biological role and properties, functional properties and technological applications of RG-II. Particular emphasis is given on the description of the three-dimensional structures of RG-II, in its monomeric and dimeric form as elucidated from the concerted investigations throughout 800 MHz NMR spectroscopy, light scattering, atomic force microscopy along with molecular mechanics and dynamics. Some attempts of deciphering of the structural role that RG-II may play in the cell wall of growing plants are presented.

Determination of the chemical structure of the capsular polysaccharide of strain B33, a fast-growing soya bean-nodulating bacterium isolated from an arid region of China.

We have determined the structure of a polysaccharide from strain B33, a fast-growing bacterium that forms nitrogen-fixing nodules with Asiatic and American soya bean cultivars. On the basis of monosaccharide analysis, methylation analysis, one-dimensional 1H- and 13C-NMR and two-dimensional NMR experiments, the structure was shown to consist of a polymer having the repeating unit -->6)-4-O-methyl-alpha-D-Glcp-(1-->4)-3-O-methyl-beta-D-GlcpA-(1--> (where GlcpA is glucopyranuronic acid and Glcp is glucopyranose). Strain B33 produces a K-antigen polysaccharide repeating unit that does not have the structural motif sugar-Kdx [where Kdx is 3-deoxy-D-manno-2-octulosonic acid (Kdo) or a Kdo-related acid] proposed for different Sinorhizobium fredii strains, all of them being effective with Asiatic soya bean cultivars but unable to form nitrogen-fixing nodules with American soya bean cultivars. Instead, it resembles the K-antigen of S. fredii strain HH303 (rhamnose, galacturonic acid)n, which is also effective with both groups of soya bean cultivars. Only the capsular polysaccharide from strains B33 and HH303 have monosaccharide components that are also present in the surface polysaccharide of Bradyrhizobium elkanii strains, which consists of a 4-O-methyl-D-glucurono-L-rhamnan.

Studies on the solution conformation and dynamics of a polysaccharide from Sinorhizobium fredii HH103 and its monosaccharide repeating unit.

The conformational behavior of the homopolysaccharide isolated from Sinorhizobium fredii HH103 and its monosaccharide repeating unit (5-acetamido-3,5,7,9-tetradeoxy-7-(3-hydroxybutyramido)-L-glycero- L- manno-nonulosonic acid) was analyzed by nuclear magnetic resonance (NMR) spectroscopy and extensive molecular dynamics simulations (MD). The results indicate that the glycosidic linkages and lateral chains may adopt a variety of conformations. MD simulations using the generalized Born solvent-accessible surface area (GB/SA) continuum solvent model for water and the MM3* force field provide a population distribution of conformers that satisfactorily agrees with the experimental NMR data for the torsional degrees of freedom of the molecule.

Structural determination of a 5-acetamido-3,5,7, 9-tetradeoxy-7-(3-hydroxybutyramido)-L-glycero-L-manno-nonulos onic acid-containing homopolysaccharide isolated from Sinorhizobium fredii HH103.

The structure of a polysaccharide from Sinorhizobium fredii HH103 has been determined. This polysaccharide was isolated by following the protocol for lipopolysaccharide extraction. On the basis of monosaccharide analysis, methylation analysis, fast atom bombardment MS, matrix-assisted laser desorption ionization MS, electron-impact high-resolution MS, one-dimensional (1)H-NMR and (13)C-NMR and two-dimensional NMR experiments, the structure was shown to consist of a homopolymer of a 3:1 mixture of 5-acetamido-3,5,7, 9-tetradeoxy-7-[(R)- and (S)-3-hydroxybutyramido]-l-glycero-l-manno-nonulosonic acid. The sugar residues are attached via a glycosidic linkage to the OH group of the 3-hydroxybutyramido substituent and thus the monomers are linked via both glycosidic and amidic linkages. In contrast with the Sinorhizobium K-antigens previously reported, which are composed of a disaccharide repeating unit, the K-antigen polysacharide of S. fredii HH103 is a homopolysaccharide.

Structural determination of a 5-O-methyl-deaminated neuraminic acid (Kdn)-containing polysaccharide isolated from Sinorhizobium fredii.

The structure of a polysaccharide from Sinorhizobium fredii SVQ293, a thiamine auxotrophic mutant of S. fredii HH103, has been determined. This polysaccharide was isolated following the protocol for lipopolysaccharide extraction. On the basis of monosaccharide analysis, methylation analysis, fast atom bombardment MS, collision-induced dissociation tandem MS, one-dimensional 1H and 13C NMR and two-dimensional NMR experiments, the structure was shown to consist of the following trisaccharide repeating unit-->2)-alpha-d-Galp-(1-->2)-beta-d-Ribf-(1-->9)-alpha-5-O-Me-++ +Kdnp- (2-->, in which Kdn stands for deaminated neuraminic acid; 25% of the Kdn residues are not methylated. The structure of this polysaccharide is novel and this is the first report of the presence of Kdn in a rhizobial polysaccharide, as well as being the first structure described containing 5-O-Me-Kdn. This Kdn-containing polysaccharide is not present in the wild-type strain HH103, which produces a 3-deoxy-d-manno-2-octulosonic acid (Kdo)-rich polysaccharide. We conclude that it is likely that the appearance of this new Kdn-containing polysaccharide is a consequence of the mutation.

Structural analysis of the exopolysaccharides produced by Lactobacillus spp. G-77.

The exopolysaccharide produced by a ropy strain of Lactobacillus spp. G-77 in a semi-defined medium, was found to be a mixture of two homopolymers composed of D-Glc. The two poly-saccharides were separated and, on the basis of monosaccharide and methylation analyses, 1H, 13C, 1D and 2D NMR experiments, one of the polysaccharides was shown to be a 2-substituted-(1-3)-beta-D-glucan, identical to that described for the EPS from Pediococcus damnosus 2.6 (M.T. Dueñas-Chasco, M.A. Rodríguez-Carvajal, P. Tejero-Mateo, G. Franco-Rodríguez, J. L. Espartero, A. Irastorza-Iribar, and A.M. Gil-Serrano, Carbohydr. Res., 303 (1997) 453-458), and the other polysaccharide was shown to consist of repeating units with the following structure [formula: see text]

Structural analysis of the exopolysaccharide produced by Pediococcus damnosus 2.6.

The exopolysaccharide produced by a ropy strain of Pediococcus damnosus (2.6) in a semi-defined medium was found to be an homopolymer composed of D-glucose. On the basis of monosaccharide and methylation analysis, 1H, 13C, 1D and 2D NMR experiments the polysaccharide was shown to consist of repeating units with the following structure. [sequence: see text]