Sensors, Volume 6, Issue 11 (November 2006) – 15 articles , Pages 1428-1720

The thermal stability of aqueous polyurethanes has been measured applying thethermogravimetric analysis. The aqueous polyurethanes (aqPUR) with catalysts of differentselectivity have been studied by use of the dynamic method. To obtain degradations of 0.025,0.05, and 0.10, employing the dynamic method, the heating rates of 0.5, 1, 2, 5, and 10 °Cmin-1 have been used in the range of 30-500 ºC. Using the more selective catalysts in theaqueous polyurethanes, the total resulting time of the decompositon has been on the increaseat all degrees of the degradation and at the particular starting temperature. This paper showsthat the dynamic method based on the thermogravimetric analysis can be used to assess thethermal stability of the aqueous polyurethanes using the catalysts of different selectivity. Full article

A portable, low cost sensing system is described which interfaces to an electronictongue sensor. The sensor used is a voltammetric sensor which monitors electrochemicalreactions that occur in solutions. The sensor is able to test a range of liquids with differentelectrochemical properties without any hardware adjustments to the system. The system canautomatically adjust for the change in solution properties by performing a routine whichuses an auto-ranging feature to determine a current-to-voltage conversion of the sensor databy using a binary search strategy. This eliminates the intervention of the user to modify thesystem each time a new solution is tested. The effectiveness of the calibration routine wastested by carrying out cyclic voltammetry in two different solutions, 0.1M sulfuric acidsolution and the phosphate buffered solution of pH3. The sensor system was able toaccurately acquire the sensor data for each solution. Full article

Weak gaseous plume detection in hyperspectral imagery requires thatbackground clutter consisting of a mixture of components such as water, grass, and asphaltbe well characterized. The appropriate characterization depends on analysis goals.Although we almost never see clutter as a single-component multivariate Gaussian(SCMG), alternatives such as various mixture distributions that have been proposed mightnot be necessary for modeling clutter in the context of plume detection when the chemicaltargets that could be present are known at least approximately. Our goal is to show to whatextent the generalized least squares (GLS) approach applied to real data to look for evidenceof known chemical targets leads to chemical concentration estimates and to chemicalprobability estimates (arising from repeated application of the GLS approach) that aresimilar to corresponding estimates arising from simulated SCMG data. In some cases,approximations to decision thresholds or confidence estimates based on assuming the clutterhas a SCMG distribution will not be sufficiently accurate. Therefore, we also describe astrategy that uses a scene-specific reference distribution to estimate decision thresholds forplume detection and associated confidence measures. Full article

The latest investigations on producing more efficient catalytic aqueouspolyurethane systems are in the domain of metal complexes with mixed ligands. In ourprevious research works, the high selectivity for the isocyanate-hydroxyl reaction inaqueous polyurethane systems has been shown by the manganese(III) mixed-ligandcomplexes. The two new complexes have been prepared with two acetylacetonate (acac)ligands and one maleate ligand and its hydroxylamine derivative of the general formula[Mn(C₅H₇O₂)₂L]. Their structures have been established by using the fundamental analyses,the FTIR and UV/VIS spectroscopic methods, as well as the magnetic measurements. Inorder to explain the different selectivity of the manganese(III) mixed-ligand complexes, theUV and ESR spectroscopy have been employed to determine the kinetics of the complexes’decomposition. The thermal stability of the complexes has been determined by way of thedynamic TG method at the heating rate of 5°C⋅min^-1 and at the temperature ranged 20-550°C. It suggests the decomposition of the complexes by loss of acid ligand. The main factor in the selective catalysis control in theaqueous polyurethane systems is the nature of the acid ligands and their impact on themanganese(II)/manganese(III) equilibrium. Full article

Airborne chemical sensing with mobile robots has been an active research areasince the beginning of the 1990s. This article presents a review of research work in this field,including gas distribution mapping, trail guidance, and the different subtasks of gas sourcelocalisation. Due to the difficulty of modelling gas distribution in a real world environmentwith currently available simulation techniques, we focus largely on experimental work and donot consider publications that are purely based on simulations. Full article

A method of wet chemical synthesis suitable for high throughput and combinatorial applications has been developed for the synthesis of porous resistive thick-film gas sensors. This method is based on the robot-controlled application of unstable metal oxide suspensions on an array of 64 inter-digital electrodes positioned on an Al₂O₃ substrate. SnO₂, WO₃, ZrO₂, TiO₂, CeO₂, In₂O₃ and Bi₂O₃ were chosen as base oxides, and were optimised by doping or mixed oxide formation. The parallel synthesis of mixed oxide sensors is illustrated by representative examples. The electrical characteristics and the sensor performance of the films were measured by high-throughput impedance spectroscopy while supplying various test gases (H₂, CO, NO, NO₂, propene). Data collection, data mining techniques applied and the best potential sensor materials discovered are presented. Full article

The construction and characterization of a flow-through polarographic detectorfor catalyzing the electroreduction of N-nitrosodiethanolamine (NDELA), is discussed. Theflow-through cell is equipped with a gold wire electrode (a thin mercury film deposited on agold substance). The response is evaluated with respect to substance diameter, length,concentration of modifying film, operating potential, supporting electrolyte and pH, andflow rate in the DC mode. The system allows the determination of N-nitrosodiethanolaminein rabbit biological fluids with relatively inexpensive equipment. Full article

Arrays of chemical sensors, usually called electronic noses (ENose), are widelyused in industry for classifying and identifying odours. They may also be used to locate theposition and detect the direction of an emission source. Usually this task is performed by anENose cooperating with a mobile vehicle, but when a source is instantaneous, or thesurrounding terrain is hard for vehicles to traverse, an alternative approach is needed. Thus athree-step method for a stationary ENose with a novel structure to detect the direction of adynamic source is presented in this paper. The method uses the ratio of measuredconcentration from different sensors (C_n /C₁ where n=2, 4) as a discriminator. In addition,this method could easily be adapted to robotics as an optimized algorithm for path trackingto a source location. The paper presents the results of a simulation of the method. Full article

An improvement of selectivity for electrochemical detection of dopamine (DA)with differential pulse voltammetry is achieved by covalently modifying a glassy carbonelectrode (GCE) with O-carboxymethylchitosan (OCMCS). The amphiphilic chitosanprovides electrostatic accumulation of DA onto the electrode surface. In a phosphate buffersolution (pH 6.0), a pair of well-defined reversible redox waves of DA was observed at theOCMCS/GCE with a δE_p of 52 mV. The anodic peak current obtained from thedifferential pulse voltammetry of dopamine was linearly dependent on its concentration inthe range of 6.0 × 10^-8 to 7.0 × 10^-6 M, with a correlation coefficient of 0.998. Thedetection limit (S/N = 3) was found to be 1.5 × 10^-9 M. The modified electrode had beenapplied to the determination of DA in human serum samples with satisfactory results. Full article

The response of an amperometric biosensor at mixed enzyme kinetics anddiffusion limitations was modelled digitally in the case of substrate inhibition. Digitalsimulations were carried out using a finite difference technique. Calculations showedcomplex kinetics of biosensor response. At low enzyme activity and substrate concentration(S0), the response of the sensor looks like it is limited by a simple substrate diffusion. Atsubstrate concentration comparable to the Michaelis-Menten constant (KM), the responsechange shows a maximal value. A sharp response change was indicated at high enzymeactivity and high (4.9 > S0/KM > 4.5) substrate concentration. This was explained by multiconcentrationof substrate generation inside the enzyme layer. This conclusion wasconfirmed by the analytical solution of the simplified biosensor model with externaldiffusion limitation at steady-state conditions. The complex kinetics of response changeproduces different calibration graphs for biosensor response at transition and steady state. Full article

Miniaturization and integration of chemical devices into modules that aredimensionally comparable with electronic chips (Lab on Chip) is nowadays developingworldwide. The aim of our work was to suggest and optimize the best conditions forfabrication of TFT sensor due to its sensitivity and low experimental deviations. Newelectrochemical analytical device was developed to ensure certain known mass transport toelectrodes, which is the most limiting process that influencing the response quality of thesensor. The device consists from rotating conic vessel for measured sample and stick-inthick-film sensor. The sensors responses were tested under trace analysis of cadmium.Measurements were done also with the others electrochemical arrangements to comparewith the new one. The sensor output current response dependence on the liquid velocity andgeometrical arrangement within using standard electrochemical couple of potassiumferrocyanide-ferricyanide is presented. We found out that the new device with controlledflow of electrolyte to sensor worked properly and gave satisfactory results. Full article

Acetylsalicylic acid (AcSA), or aspirin, was introduced in the late 1890s and hasbeen used to treat a variety of inflammatory conditions. The aim of this work was to suggestelectrochemical sensor for acetylsalicylic detection. Primarily, we utilized square wavevoltammetry (SWV) using both carbon paste electrode (CPE) and of graphite pencilelectrode (GPE) as working ones to indirect determination of AcSA. The principle ofindirect determination of AcSA bases in its hydrolysis on salicylic acid (SA), which isconsequently detected. Thus, we optimized both determination of SA and conditions forAcSA hydrolysis and found out that the most suitable frequency, amplitude, step potentialand the composition and pH of the supporting electrolyte for the determination of SA was260 Hz, 50 mV, 10 mV and Britton-Robinson buffer (pH 1.81), respectively. The detectionlimit (S/N = 3) of the SA was 1.3 ng/ml. After that, we aimed on indirect determination ofAcSA by SWV CPE. We tested the influence of pH of Britton-Robinson buffer andtemperature on yield of hydrolysis, and found out that 100% hydrolysis of AcSA wasreached after 80 minutes at pH 1.81 and 90°C. The method for indirect determination ofAcSA has been utilized to analyse pharmaceutical drug. The determined amount of AcSA in the pharmaceutical drug was in good agreement with the declared amounts. Moreover, weused GPE for determination of AcSA in a pharmaceutical drug. Base of the results obtainedfrom stationary electrochemical instrument we used flow injection analysis withelectrochemical detection to determine of salicylates (SA, AcSA, thiosalicylic acid, 3,5-dinitrosalicylic acid and 5-sulfosalicylic acid – SuSA). We found out that we are able todetermine all of detected salicylates directly without any pre-treatment, hydrolysis and so onat units of femtomoles per injection (5 μl). Full article

Naphthoquinones are one of the groups of secondary metabolites widespread innature, where they mostly appear as chromatic pigments. They embody broad-range ofbiological actions from phytotoxic to fungicidal. An anticancer effect of naphthoquinonesstimulates an interest in determination and characterization of single derivatives of 1,2- and1,4-quinones in biological samples. The main aim of this work was to suggest a techniquesuitable to determine lawsone, juglone and/or plumbagin in biological samples and to studyof their influence on BY-2 tobacco cells. The BY-2 tobacco cells were cultivated in thepresence of the naphthoquinones of interest (500 μg.l^-1) for 24 h and then the morphologicalchanges were observed. We found out that naphthoquinones triggered the programmed celldeath at BY-2 cells, which can be confirmed by the apoptotic bodies in nucleus. After thatwe suggested and optimized different electrochemical techniques such differential pulsevoltammetry (DPV) coupled with hanging mercury drop (HMDE) and carbon pasteelectrode, micro flow device coupled with carbon screen printed electrodes and flowinjection analysis coupled with Coulochem III detector to determine them. The detectionlimits of naphthoquinones of interest were expressed as 3S/N and varied from units tohundreds of ng per millilitres according to methods used. Moreover, we utilized DPVcoupled with HMDE and micro flow device to determine content of juglone in leavesPersian walnut (Juglans regia). We determined that the leaves contained juglone tenths of gper 100 g of fresh weight. The results obtained show the convincing possibilities of using ofthese methods in analysis of plant secondary metabolites. Full article

Volatile organic compound (VOC) detection is a topic of growing interest withapplications in diverse fields, ranging from environmental uses to the food or chemicalindustries. Optical fiber VOC sensors offering new and interesting properties whichovercame some of the inconveniences found on traditional gas sensors appeared over twodecades ago. Thanks to its minimum invasive nature and the advantages that optical fiberoffers such as light weight, passive nature, low attenuation and the possibility ofmultiplexing, among others, these sensors are a real alternative to electronic ones inelectrically noisy environments where electronic sensors cannot operate correctly. In thepresent work, a classification of these devices has been made according to the sensingmechanism and taking also into account the sensing materials or the different methods offabrication. In addition, some solutions already implemented for the detection of VOCsusing optical fiber sensors will be described with detail. Full article

Over the last twenty years, newly developed chemical sensor systems (socalled“electronic noses") have odour analyses made possible. This paper describes theapplications of these systems for microbial detection in different fields such as medicineand the food industry, where fast detection methods are essential for appropriatemanagement of health care. Several groups have employed different electronic noses forclassification and quantification of bacteria and fungi to obtain accurate medicaldiagnosis and food quality control. So far, detection and identification of bacterial andfungal volatiles have been achieved by use of e-noses offering different correctclassification percentages. The present review includes examples of bacterial and fungalspecies producing volatile compounds and correlated to infectious diseases or fooddeterioration. The results suggest the possibility of using this new technology both inmedical diagnostics and in food control management. Full article