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Microelectrode arrays (MEAs) are gaining interest in electroanalysis owing to its distinctive voltammetry properties compared to its macro counterparts. Among the MEAs widely fabricated and studied are microdisc array and microband array. We report here the microfabrication of 10 μm microband array (number of band in an array, N=17) and its application in labelless impedimetric sensing of T-2/HT-2 toxin. The microband array has recess depth (i.e. Si3N4 passivation thickness) of 200 nm. Upon fabrication, the device was first characterized via visual inspection and electrochemical analysis. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies were performed in 1 mM ferrocenecarboxylic acid (FCA) in 0.01 M PBS, pH 7.4. At scan rate of 100 mv s-1, cyclic voltammogram for the microband array exhibited a slight peak-shaped CV; and was found to be scan-rate dependent. Experimental limiting current of the microband array (529±7 nA) was slightly lower compared to the calculated theoretical current (632 nA) indicating mixed diffusion profile of the microband array. The device was then employed in immunosensor construction for T-2/HT-2 toxins detection. T-2 mycotoxin and its metabolite (HT-2), are target of concern in the biosensing application due to its lethal toxicity and prominent presence in EU grains industry. Surface functionalization for anti-T-2 monoclonal antibody (mAb) immobilization was first achieved via surface hydroxylation with plasma cleaning and piranha solution treatment, followed by (3-Aminopropyl) triethoxysilane (APTES) silanization and 15 minutes pre-incubation with various concentrations of anti-T-2 toxin mAb in EDC/NHS mixture. The optimal concentrations for anti-T-2 toxin mAb immobilization on the microband array surface was determined at 0.75 mg mL-1. Based on the calibration curve developed in buffer solution system, the functionalized microband array was proven sensitive as it was able to detect T-2/HT-2 toxin at low dynamic working range (0-25 ppb) and limit of quantitation (LOQ) achieved at 4.89 ppb.

Nucleophilic substitution of a chlorine atom in 4,5 dichloro-1,2-dithiole-3-thione with per-O-acetyl-1-mercaptho derivatives of d-glucose, d-galactose, d-mannose, d-xylose, l-arabinose, and d-maltose gave six new acetylthioglycoside conjugates of 4-chloro-1,2-dithiole-3-thione. These thioglycosides were shown to possess cancer preventive activity on the models of JB6 Cl41 P+ mouse epidermal cells and THP-1 human leukemia cells in soft agar, as well as to inhibit the AP-1-dependent transcriptional activity in JB6 Cl41 luc-AP-1 cells, which suggests the possibility of using the new compounds as potential cancer preventive drugs.

A convenient synthesis of new 8-oxa-2-azaspiro[4.5]decane from commercially available reagents based on tetrahydropyran-4-carbonitrile and 1-bromo-2-fluoroethane has been developed. This compound is promising for the production of important biologically active compounds.

An efficient synthesis of [1,2,5]oxadiazolo[3,4-d]pyridazine 1,5,6-trioxides (1) from 3,4-bis(hydroxyimino)methyl)-1,2,5-oxadiazole 2-oxides using a mixture of concentrated nitric and trifluoroacetic acids has been developed. The scope of the unconventional reaction was established. The 4,7-dinitro[1,2,5]oxadiazolo[3,4-d]pyridazine 1,5,6-trioxide 1f represents a new high energy compound, unfortunately with low thermal stability. The parent [1,2,5]oxadiazolo[3,4-d]pyridazine 1,5,6-trioxide 1c was studied by single-crystal X-ray diffraction analysis which revealed a planar molecule with an unusually long intracyclic N N bond of 1.668(5) A and unexpected exo-cyclic bond angles at the nitroxyl nitrogen atoms. In the crystal, the molecules of 1c are bound to each other by strong π-π stacking and C H⋯O hydrogen bonding interactions into a three-dimensional framework that results in a high crystal density of 1.833 gcm−3.

A novel 4-chloro-6-(chloromethyl)-1-methyl-1H-pyrazolo[3,4-d]pyrimidine was prepared by a rational and short two-step synthesis from commercially available ethyl 5-amino-1-methyl-1H-pyrazole-4-carboxylate via 6-(chloromethyl)-1-methyl-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one. The structure of the synthesized compounds was established by elemental analysis, high-resolution mass-spectrometry, 1H, 13C-NMR and IR spectroscopy and mass-spectrometry. 4-Chloro-6-(chloromethyl)-1-methyl-1H-pyrazolo[3,4-d]pyrimidine is a convenient intermediate for various disubstituted 1-methyl-1H-pyrazolo[3,4-d]pyrimidines, which may be of interest as substances with useful pharmacological properties.

A versatile one-pot synthesis of 4-substituted 3-(nitrooxyalkyl)furoxans by the reaction of 3-alkylfuroxans with a mixture of nitric and sulfuric acids was developed. A plausible mechanism of this unusual transformation was explained in terms of a new Grob-type fragmentation.

A short and efficient synthesis of 1-(2-oxido-1,2,5-oxadiazol-3-yl)alkyl nitrates from 3-alkyl-1,2,5-oxadiazole 2-oxides, using a mixture of nitric and sulfuric acids in chloroform, has been developed. The scope of the unconventional reaction was established; its mechanism likely included a new Grob-type fragmentation.

The gastrointestinal (GI) tract, especially the small intestine, remains largely inaccessible to modern medical science. While swallowable capsule technologies are emerging, endoscopy and colonoscopy remain the primary method for GI tract analysis. This paper presents an alternative wireless device, with electrochemical sensing technique, which behaves autonomously as it travels through the GI tract. The capsule includes a direct access, multi electrode electronic tongue sensor that enables non-specific characterization of gut fluids, aiding in the diagnosis of gastrointestinal diseases such as Crohn's and ulcerative colitis. The sensor, interfaced through a potentiostatic circuit, is capable of performing various voltammetries such as cyclic, square wave and differential pulse techniques. A wireless communication link, operating at 433 MHz, delivers measured data to a base station receiver located outside the body. The capsule, powered by a single lithium-ion cell and implemented on a polyimide flexible substrate, is encapsulated in polyether ether ketone (PEEK) material to measure 12 mm in diameter and 28 mm in length taking volume of approximately 4 cm 3 . The capsule's front end potentiostat compares well with commercial laboratory equipment under the same cell and voltammetry conditions. The electrochemical characterization of the system and its application for electrochemical examination of faecal waters proves its potential as an in vivo GI tract diagnostic tool and other biomedical applications requiring a miniaturized low power sensing device.

The application of solid-state nanopore technology for biosensing is a rapidly developing area of research with high commercial potential. Different synthetic materials, including silicon nitride, alumina, and polymers, are employed to fabricate single and multiple pores and offer a good platform for selective biomolecule detection. Two solid-state pore arrays, one with integrated silicon microfluidic system, were considered and an immobilization strategy suitable for detecting a single-stranded DNA (ssDNA) sequence was investigated. For the silicon nitride pores, a modification method based on the use of 3-aminopropyltriethoxysilane for silanization and 1,4-phenylene diisothiocyanate for amine crosslinking was applied to immobilize 100-nM ssDNA (amine C6) and a 100-nM limit of detection for complementary to probe ssDNA (Cy5) was estimated. The polycarbonate pores (the second type of the pore arrays) underwent surface modification based on an oxidation reduction reaction using sodium periodate and sodium borohydride and was used to immobilize 10-nM ssDNA and an estimated 100-nM limit of detection was also achieved. Linear sweep voltammetry was used to characterize the pores and a current potential profile was obtained after both immobilization of probe ssDNA and hybridization of complementary to probe ssDNA on the modified pore array surface. A decrease in current amplitude was measured after surface modification of both pore arrays, and this was attributed to the appearance of an additional layer on the pore surface reducing the pore opening and hindering the current flow. The hybridization event was also supported by contact angle measurements, where an increase in hydrophilicity was recorded at the different surface modification steps that were applied to produce the biofunctionalized nanopore. In addition, fluorescence was observed on the surfaces after hybridization, through incorporation of a CY5 fluorescent tag attached on the 5’ end of the complementary to probe DNA. These results show the potential to use both silicon nitride and polycarbonate nanopores in DNA detection applications.

A nanoporous gold (NPG) microdisc array in a three-electrode electrochemical cell arrangement has been fabricated and characterised for a dissolved oxygen sensing application. The device will be used for monitoring of drinking water quality in rural communities in India, where there is a need for a miniaturised, low-cost dissolved oxygen sensor. The NPG microdisc array exhibits improved electrochemical responses compared to a planar gold microdisc array, owing to its extended surface area. In 1 mM ferrocene carboxylic acid, the experimental limiting currents obtained are twice as large as the theoretical limiting current for a planar gold microarray. A 252-nm-thick NPG layer resulted in a limiting current of 627 nA (compared to the estimated current of 295 nA). The voltammetric behaviour in water samples from a pilot site in India was investigated for increasing oxygen content, and a comparison was made with a macrodisc gold electrode and an unmodified microdisc array. The NPG microdisc array demonstrated improved characteristics over both devices and exhibited a higher correlation (average value 0.925) compared with the unmodified array (0.819) and macrodisc (0.870). An improvement in signal-to-noise ratio was also observed to be 12.349 versus 5.259 (microelecrode array) and 5.604 (macroelectrode). The response time for the NPG microdisc array versus a commercial dissolved oxygen sensor showed a faster response time of 20 versus 40 s.

Electrochemical sensing systems are advancing into a wide range of new applications, moving from the traditional lab environment into disposable devices and systems, enabling real-time continuous monitoring of complex media. This transition presents numerous challenges ranging from issues such as sensitivity and dynamic range, to autocalibration and antifouling, to enabling multiparameter analyte and biomarker detection from an array of nanosensors within a miniaturized form factor. New materials are required not only to address these challenges, but also to facilitate new manufacturing processes for integrated electrochemical systems. This paper examines the recent advances in the instrumentation, sensor architectures, and sensor materials in the context of developing the next generation of nanoenabled electrochemical sensors for life sciences applications, and identifies the most promising solutions based on selected well established application exemplars.

The fabrication of on-chip microelectrochemical cell on Si wafer by means of photolithography is described here. The single on-chip microelectrochemical cell device has dimensions of 100 × 380 mm with integrated Pt counter electrode (CE), Ag/AgCl reference electrode (RE) and gold microelectrode array of 500 nm recess depth as the working electrode (WE). Two geometries of electrode array were implemented, band and disc, with fixed diameter/width of 10 µm; and varied centre-to-centre spacing (d) and number of electrodes (N) in the array. The on-chip microelectrochemical cell structure has been designed to facilitate further WE biomodifications. Firstly, the developed microelectrochemical cell does not require packaging hence reducing the production cost and time. Secondly, the working electrode (WE) on the microelectrochemical cell is positioned towards the end of the chip enabling modification of the working electrode surface to be carried out for surface bio-functionalisation without affecting both the RE and CE surface conditions. The developed on-chip microelectrochemical cell was examined with scanning electron microscopy (SEM) and characterised by two electrochemical techniques. Both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed in 1 mM ferrocenecarboxylic acid (FCA) in 0.01 M phosphate buffered saline (PBS) solution at pH7.4. Electrochemical experiments showed that in the case of halving the interspacing distance of the microdisc WE array (50 nm instead of 100 nm), the voltammogram shifted from a steady-state CV (feature of hemispherical diffusion) to an inclined peak-shaped CV (feature of linear diffusion) albeit the arrays had the same surface area. In terms of EIS it was also found that linear diffusion dominates the surface instead of hemispherical diffusion once the interspacing distance was reduced, supporting the fact that closely packed arrays may behave like a macroelectrode.

Heptasulfur imides substituted by hereterocycle may be of interest as biologically active compounds. In this communication, the reaction of pyrimidin-2-amine 1 with disulfur dichloride was carefully investigated to give 8-(pyrimidin-2-yl)-1,2,3,4,5,6,7,8-heptathiazocane in good yield. The structure of the newly synthesized compound was established by means of elemental analysis, high resolution mass-spectrometry, 1H, 13C NMR and IR spectroscopy and mass-spectrometry.

4H-3λ2-Thieno[3,2-d]pyrimidin-4-one derivatives are of interest as biologically active compounds. In this communication, 2-(chloromethyl)-4H-3λ2-thieno[3,2-d]pyrimidin-4-one (1) was investigated in the reaction with ammonia, potassium phthalimide, and other basic agents. The dimerization product—8,18-dithia-1,4,11,14-tetrazapentacyclo[11.7.0.03,11.05,9.015,19]icosa-3,5(9),6,13,15(19),16-hexaene-10,20-dione was formed in the reaction with potassium phthalimide in DMF, by heating at 110 °C for 5 h. The structure of the newly synthesized compound was established by means of elemental analysis, high resolution mass-spectrometry, 1H, 13C NMR, and IR spectroscopy, and mass-spectrometry.

We compared three optical platforms for measurement of cellular respiration: absolute oxygen consumption rates (OCRs) in hermetically sealed microcuvettes, relative OCRs measured in a 96-well plate with oil seal, and steady-state oxygenation of cells in an open 96-well plate. Using mouse embryonic fibroblasts cell line, the phosphorescent intracellular O2 probe MitoXpress-Intra, and time-resolved fluorescence reader, we determined algorithms for conversion of relative OCRs and cell oxygenation into absolute OCRs, thereby allowing simple high-throughput measurement of absolute OCR values.

Benzo- and pyridoannulated 1,2-dithiole-3-thiones react with compounds containing an activated methyl group such as 1-methyl-3,4-dihydropyrrolo[1,2-a]pyrazine and 2-methylpyridines to furnish substituted 1,2-dithiol-3-ylidenes.

A short and efficient synthesis of 1-(2-oxido-1,2,5-oxadiazol-3-yl)alkyl nitrates from 3-alkyl-1,2,5-oxadiazole 2-oxides, using a mixture of nitric and sulfuric acids in chloroform, has been developed. The scope of the unconventional reaction was established; its mechanism likely included a new Grob-type fragmentation.

Chemical modifications on recessed microelectrode array, achieved via electrodeposition techniques are reported here. Silicon-based gold microelectrode arrays of 10 μm microband and microdisc array were selected and functionalised using sol-gel and nanoporous gold (NPG) respectively. For electrochemically assisted self-assembly (EASA) formati6154on of sol-gel, electrode surface was first pre-treated with a self-assembled partial monolayer of mercaptopropyltrimethoxysilane (MPTMS) before transferring it into the sol containing cetyltrimethyl ammonium bromide (CTAB)/tetraethoxysilane (TEOS):MPTMS (90:10) precursors. A cathodic potential is then applied. It was found that larger current densities were required in ensuring successful film deposition when moving from macro- to micro- dimensions. For NPG modification, a chemical etching process called dealloying was employed. NPG of three different thicknesses have been successfully deposited. All the modified and functionalized microelectrode arrays were characterized by both optical (SEM) and electrochemical analysis (cyclic voltammetry and impedance spectroscopy). An increase in surface area and roughness has been observed and such will benefit for future sensing application.

Aims To evaluate high-throughput optical oxygen microrespirometry for selective detection and predictive identification of aerobic bacteria. Methods and Results Using GreenLight probe, standard 384-well plates and time-resolved fluorescence reader, a representative panel of 16 partially selective media and 9 aerobic bacteria (Escherichia coli, Bacillus cereus, Staphylococcus aureus, Campylobacter jejuni, Yersinia enterocolitica, Pseudomonas aeruginosa, Streptococcus pyogenes, Salmonella typhimurium and Listeria innocua) were analysed. For each medium, bacterial strain and dilution, growth profiles were recorded, from which calibrations, doubling/generation times and growth patterns in different media were determined. Analytical performance, selectivity and general usability of the method were assessed, and mixed bacterial cultures were analysed. Conclusion The microrespirometry platform facilitates simple, real-time detection and predictive identification of aerobic bacteria by looking at the patterns of their growth and respiration in several media and determining their growth and doubling times. Significance and Impact of the Study The new screening method can be used for routine microbiological analysis and testing of aerobic bacterial cultures as well as complex food, environmental and clinical samples.

Available data concerning the chemistry of 1,2-dithioles published over the past 15 years have been summarized and systematized. Different transformations of these compounds have been considered, including reactions with participation of substituents in the dithiole ring. The bibliography includes 96 references.

4,5-Dichloro-1,2-dithiole-3-thione was found to undergo 1,3-dipolar cycloaddition reactions with internal and terminal alkynes. The combination of these reactions together with new transformations afforded versatile heterocyclic systems including 1,3-dithioles, imino-1,3-dithietanes, 2-iminothiophen-3-ones, thienothiopyranthiones, and others.

The behaviour of an acridine-functionalised calix[4]arene at the interface between two immiscible electrolyte solutions (ITIES) is reported. Molecular modelling showed that the acridine-calix[4]arene has regions of significant net positive charge spread throughout the protonated acridine moieties, consistent with it being able to function as an anion ionophore. The presence of this compound in the organic phase facilitated the transfer of aqueous phase electrolyte ions. Upon addition of double stranded DNA to the aqueous phase, the transfer of electrolyte anions was diminished, due to DNA binding to the acridine moiety at the ITIES. The behaviour provides a basis for DNA hybridization detection using electrochemistry at the ITIES.

The reaction of 1,2-dithiol-3-thiones with isonitriles at room temperature affords imino-1,3-dithietanes. The reaction is reversible. According to 1H NMR spectroscopy, the rise of the temperature shifts the equilibrium to the starting compounds. The structure of one of the imino-1,3-dithietanes was established by X-ray diffraction.

Voltammetric methods use a constant sweep rate during the course of a scan. This paper reports a study of the influence of a nonconstant sweep rate on the voltammetric response. In this approach, either continuously increasing or continuously decreasing potential scan rates can be employed, unlike presently available methods which rely on a constant sweep rate. The voltammetric response of potassium ferrocyanide at a glassy carbon electrode was used as a model system to test the new method. The responses obtained using traditional staircase voltammetry (linear staircase voltammetry) and the new approach (nonlinear staircase voltammetry) were compared by experiment and by simulation. The new approach offers capability for signal enhancement, whereby enhanced current or enhanced peak shape can be obtained by choice of appropriate waveform parameters.

A simple and efficient data analysis algorithm for biological oxygen consumption assays based on quenched-fluorescence oxygen sensing is presented. The algorithm allows the linearization of raw fluorescence profiles in transformed co-ordinates thereby facilitating data processing and generating accurate results for multiple samples analysed in parallel on a fluorescence reader. This approach provides stability with respect to the uncertainty of the reaction start time, it allows on-the-flight determination of kinetic parameters by pairwise reading method, and additional filtration of raw data leading to improved accuracy. This methodology was validated with three independent sets of data from the analysis of activity and inhibition of isolated rat liver mitochondria representing a complex oxygen-dependent enzymatic system. It demonstrated good performance allowing accurate determination of enzymatic parameters from simple linear regression analysis (R2 as high as 0.999), good correlation with simulated data and general convenience.

Mitochondrial dysfunction has been associated with a variety of currently marketed therapeutics and has also been implicated in many disease states. Alterations in the rate of oxygen consumption are an informative indicator of mitochondrial dysfunction, but the use of such assays has been limited by the constraints of traditional measurement approaches. Here, we present a high-throughput, fluorescence-based methodology for the analysis of mitochondrial oxygen consumption using a phosphorescent oxygen-sensitive probe, standard microtitre plates and plate reader detection. The protocol describes the isolation of mitochondria from animal tissue, initial establishment and optimization of the oxygen consumption assay, subsequent screening of compounds for mitochondrial toxicity (uncoupling and inhibition), data analysis and generation of dose-response curves. It allows dozens of compounds (or hundreds of assay points) to be analyzed in a single day, and can be further up-scaled, automated and adapted for other enzyme- and cell-based screening applications.

Mitochondrial dysfunction is a common mechanism of drug-induced toxicity. Early identification of new chemical entities (NCEs) that perturb mitochondrial function is of significant importance to avoid attrition in later stages of drug development. One of the most informative ways of assessing mitochondrial dysfunction is by measuring mitochondrial oxygen consumption. However, the conventional polarographic method of measuring oxygen consumption is not amenable to high sample throughput or automation. We present an alternative, low-bulk, high-throughput approach to the analysis of isolated-mitochondrial oxygen consumption using luminescent oxygen-sensitive probes. These probes are dispensable and are analyzed in standard microtitre plates on a fluorescence plate reader. Respiratory substrate and adenosine diphosphate (ADP) dependencies of mitochondrial oxygen consumption were assessed using the fluorescence-based method, and results compared favourably to conventional polarographic analysis. To assess assay performance, the method was then applied to the analysis of a panel of classical modulators of oxidative phosphorylation. The effect of uncoupler concentration was analyzed in detail to identify factors which would be important in applying this method to large scale NCE screening and mechanistic investigations. Results demonstrate that the 96-well format can accommodate up to approximately 200 compounds/day at a single concentration or alternatively IC(50) values can be generated for approximately 25 compounds. Throughput may be increased by moving to a 384-well plate format.

This study addresses the problem of specification of physical models for quenched-fluorescence-based oxygen sensors by analysing their complex frequency response (both intensity and phase signals) at different working frequencies and oxygen concentrations. Two common physical models of active medium, the single-exponential model with non-linear oxygen solubility and the double-exponential model were considered, with the example of heterogeneous PtOEPK-PS-based oxygen sensor. It was found that within the limits of experimental errors, the non-linear oxygen solubility models describe more adequately experimental data for the sensor. Model parameters were defined and analysis of the sensors system performance at different working frequencies and oxygen ranges was made.

A new modelling approach was developed which allows determination of optimal physical models and their parameters for phase-fluorometric oxygen sensors working in broad range of temperature and oxygen concentration. This approach was applied to two types of oxygen sensors based on platinum(II)-octyaethylporphine-ketone and polystyrene heat-treated and untreated sensors. Temperature behaviour of these sensors was examined using a range of physical models, including several new models with phase correction. Two common cases with different optimisation criteria were considered: (1) measurements at known sample/sensor temperature with minimal standard error (mean-square approximation) and (2) measurement at unknown (variable) sensor/sample temperature with minimal absolute error (uniform approximation). For each case, best models and accuracy of oxygen quantitation were determined. It was shown that heat treatment of the sensors provided improved temperature stability and better approximation accuracy within the studied temperature range.

The development, characterisation and evaluation of a prototype portable electrochemical trace metal analyser are presented. The instrument is a battery-powered microcontroller-based potentiostat, which implements anodic stripping voltammetry (ASV) at suitable sensor electrodes. It is capable of operating away from the laboratory, in the absence of an external power source and is usable by low-skilled personnel. The distinguishing feature of the instrument is its custom software, which enables sample pre-screening, data processing and sample dilution and standard additions calculations to be carried out. The instrument has been evaluated by application of a methodology for the detection of copper in acetic acid soil extracts, both in the laboratory and in the field. Underpotential deposition staircase anodic stripping voltammetry (UPD-SCASV) of the copper at gold disk electrodes was used as a test method. There was good agreement between the instrument results and those from laboratory-based reference analytical methods for analyses carried out both in the laboratory and in the field.

On heating with alkynes, the readily prepared 1,3-dithioles 3 undergo a new cycloaddition reaction and an unprecedented molecular rearrangement with loss of chlorine to give the first 7H-thieno[2,3-c]thiopyran-7-thiones 4 and 4H-thieno[3,2-c]thiopyran-4-thiones 5 whose structures were confirmed by X-ray diffraction. Unexpectedly, the different alkynes used to form 3 and to convert it into 4 and 5 were incorporated regiospecifically into the thiophene and thiopyran rings, respectively. [reaction: see text]

Simulation of electrochemical impedance spectroscopy (EIS) based on a LabVIEW model of a complex impedance measuring system in the frequency domain has been investigated to specify parameters of Randle's equivalent circuit, which is ordinarily used for electrode sensors. The model was based on a standard system for EIS instrumentation and consisted of a sensor modelled by Randle's equivalent circuit, a source of harmonic frequency sweep voltage applied to the sensor and a transimpedance amplifier, which transformed the sensor current to voltage. It provided impedance spectroscopy data for different levels of noise, modelled by current and voltage equivalent noise sources applied to the amplifier input. The noise influence on Randle's equivalent circuit specification was analysed by considering the behaviour of the approximation error. Different metrics including absolute, relative, semilogarithmic and logarithmic based distance between complex numbers on a complex plane were considered and compared to one another for evaluating this error. It was shown that the relative and logarithmic based metrics provide more reliable results for the determination of circuit parameters.

Gold and platinum metal electrodes on Si/SiO2 having undergone anisotropic potassium hydroxide (KOH) etch treatment are considered. This treatment etches at different rates and directions in the material resulting in creation of numerous pyramid shaped holes in the silicon substrate. This surface is used to make metal electrodes with increased electrode efficiency. The electrodes can serve as the sensors or as the sensor substrates (for surface polymer modification) and because both gold and platinum are inert they have applications for food safety biosensing. Wine, an economically significant food product, was chosen as a matrix, and impedance spectroscopy (EIS) was selected as a method of investigation of electrode behaviour. Based on results of EIS, different complexity equivalent circuits were determined by applying fitting mean square root optimisation of sensor complex impedance measurements.

An optical oxygen analyser was used in two small-scale industrial trials to non-destructively assess the quality of packaged convenience foods and packaging process. Beef lasagne packed under 70% vacuum and cooked under standard sous vide conditions was monitored for residual oxygen, using disposable sensors incorporated in each pack and a benchtop optical oxygen analyser. High levels of residual oxygen close to ambient were determined in the majority of packs after packaging, as opposed to anticipated levels of 4–5%. Residual oxygen was monitored over product shelf-life (4 weeks at +4–10°C) along with measurement of microbial growth and lipid oxidation in food by conventional destructive methods. Oxygen levels in packs went down to almost zero between weeks 2 and 3 indicating deterioration of packaged product. Correlation between oxygen profiles and the rate of microbial growth and lipid oxidation was established. The optical oxygen sensor system was shown to provide valuable information about performance of the packaging process, product storage conditions and food quality in a convenient and cost-efficient fashion and non-destructively. Copyright © 2004 John Wiley & Sons, Ltd.

A generic mathematical model was developed, which describes the integral luminescent signal (intensity and phase shift) of the quenched-luminescence oxygen sensor in the case of non-uniform distribution of the main parameters inside active medium, namely the quenching constant, oxygen and dye concentration and intensity of excitation. This approach, which describes the behaviour of various intensity-based and phase-fluorimetric oxygen sensor systems, was validated by applying it to a set of experimental calibration data obtained with heterogenous microporous sensor membranes on the basis of platinum(II)-octaethylporphine-ketone and polystyrene, and the phase-fluorimetric detector. The cases of one-, two- and three-parametric distribution of the quenching constant were analysed in detail, including discrete single- and double-exponential models and continuous distributions. The latter were represented by: Rayleigh and Maxwell distributions for one-parametric models; Gaussian, Laplace, Cauchy, Extreme Value, Logistic distributions for symmetrical two-parametric models; lognormal, Weibull, gamma and beta distributions for asymmetrical two-parametric models; mixed single-exponential model with one- and two-parametric distribution of the quenching constant-for three-parametric models. Particular models were determined, that provide satisfactory approximation with the same or smaller number of parameters than the classical single and double-exponential models. The best accuracy was achieved with: Maxwell distribution for one-parametric models; lognormal and truncated Gausian (defined only for the quenching constant values larger than distribution mode) for two-parametric models; and discrete double-exponential and mixed discrete with Maxwell distribution for three-parametric models.