Conductometric biosensors based on urease and glucose oxidase immobilized with different types of zeolites have been investigated and compared. For this purpose, zeolite A, zeolite Y, Silicalite-1 (spherical), Silicalite-2, H+Beta 300, H+Beta 150 and NH4+Beta 25 were compared as potential carriers for enzyme immobilization. The parameters to obtain optimized biosensor performance were studied by investigating the percentage of zeolite in membrane, immobilization time in glutaraldehyde vapor and pH of the environment. Different zeolite types resulted in different enzymatic responses. In particular, we have demonstrated that the urease immobilized on silicalite-2 had better performance than immobilized urease without zeolite. Conductometric biosensor with glucose oxidase immobilized with NH4+Beta 25 zeolite had similar response values compared with immobilised enzyme without zeolite. The results obtained show that zeolites could be used as alternatives for enzyme immobilization in conductometric biosensors development.

Novel modified electrodes exhibit excellent electrocatalytic performance for nitrite detection.

In this work, sensors based on molecularly imprinted polymers (MIP) for creatinine and urea selective determination using solvent evaporation processing of poly(ethylene-co-vinyl alcohol) (EVAL) to form molecularly imprinted polymers (MIP) were fabricated. The chemical behaviour of the thin film (MIP) was characterized using FTIR spectrophotometry. The carbonyl functions assigned on the spectra confirmed capture and removal (after rinsing with ethanol) of template molecule. Electrochemical impedance method was employed as transduction technique. The EIS (Electrochemical Impedance Spectroscopy) sensor response shows a limit of detection of 10 ng/mL with linear range from 0.02 mu g/mL to 3 mu g/mL for urea and 40 ng/mL of detection limit with linear range from 0.05 mu g/mL to 2 mu g/mL for creatinine with a good specificity of detection.

Pure diamond-like carbon (DLC) thin films and boron-doped DLC thin films have been deposited on silicon substrates using femtosecond pulsed laser. The amorphous carbon materials (DLC), have been deposited at room temperature by ablating graphite targets with an amplified Ti:sapphire laser of 800 nm wavelength and a pulse duration of 150 fs in high vacuum conditions. Doping with boron has been performed by ablating alternatively graphite and boron targets.In this study, the DLC films were used as working electrodes for the electrochemical detection of trace heavy metals namely, Cd2+, Pb2+, Ni2+ and Hg2+, by using square wave anodic stripping voltammetry (SWASV) technique. Four metals were detected at -1.3 V deposition potential, and 90s deposition time. The DLC films have been characterized by multiwavelength Raman spectrometry and high resolution scanning electron microscopy. The effect of the boron doping on the electrochemical behavior has been shown. The a-C:B 8%/Si3N4 electrode gives the more sensitive detection. The four metals are detected simultaneously with a detection limit of 1 mu g/L or 2 mu g/L and a dynamic range from 1 or 2 to 25 mu g/L for every metal, as presented in third table of this article. The different sensitivities obtained are 6.2, 20.0, 1.2 and 6.6 mu A/ppb or mu A mu g(-1) L for Cd2+, Pb2+, Ni2+ and Hg2+, respectively. (C) 2010 Elsevier B.V. All rights reserved.

In this work, a new miniaturized system was developed for uranium detection in waters using adsorptive stripping voltammetry associated with square wave measurements (SWAdSV). The uranium-propyl gallate (U-PG) complex accumulated at -1.4 V deposition potential, and with a 200 s deposition time, when the uranium containing sample was mixed with 0.05 mM PG in 0.05 M sodium acetate buffer (pH 4.2). The results obtained have demonstrated the capacity of the miniaturized system and the SPE microelectrodes to detect uranium, with a detection limit of 0.5 ng/L (n = 6, r(2) = 0.98), and a dynamic range from 5 ng/L to 10 mu g/L, and a sensitivity of 100 nA/mu g. (C) 2010 Published by Elsevier Ltd.

In this work, a new miniaturized system was developed for nickel and mercury detection with differential pulse anodic stripping voltammetry measurements (DPASV). The miniaturized system consists of a screen-printed microelectrode chip, a carbon working microelectrode (empty set 1 mm), an integrated Ag/AgCl reference electrode, a platinum counter electrode, and a 20 mu L PMMA microcell. The measurements with this miniaturized system were compared to measurements performed in a classical system with a glassy carbon electrode (0 3 mm). The results show that the miniaturization of the system (volume decreased by a factor of 1000 and diameter of the electrode by a factor of 3) presents several advantages: sensitivity for metal detection increased by a factor of 10 compared to a classical measuring system. The detection and quantification of Ni (II) and Hg (II) were statically performed using differential pulse anodic stripping voltammetry in the microsystem. In the Ni (II) concentration range of 0.5-550 ppb, a limit of detection of 0.15 ppb and a sensitivity of 1.489 nA/ppb are obtained. In the Hg (II) concentration range of 0.1-350 ppb, a limit of detection of 0.03 ppb and a sensitivity of 0.097 nA/ppb is obtained.

Sous la pression croissante de besoins tant reglementaires (DCE, LEMA) que cognitifs, (exploration du fonctionnement des hydro-systemes), une des tendances lourdes de la chimie environnementale actuelle est d'evoluer vers la portabilite et le suivi in situ en continu d'un nombre croissant d'analytes necessaires a la caracterisation et au suivi fonctionnel des milieux aquatiques. En effet d'une part la reglementation impose la connaissance et le suivi des teneurs d'une liste de substances dites prioritaires avec pour objectif des concentrations inferieures aux NQE (bon etat chimique) pour 2015. Et d'autre part la notion d'etat ecologique demande des avancees en hydrobiologie et ecotoxicologie qui requierent l'utilisation de metriques comparables, or actuellement des concentrations ponctuelles (analyses conventionnelles en laboratoire) sont confrontees avec des agencements biocenotiques, par nature integrateurs. Enfin les evenements polluants, singulierement perturbateurs pour les biocenoses exposees sont generalement de nature transitoire et exigent une mesure a l'instant precis du pic de pollution, necessitant la presence d'une instrumentation prete a mesurer. Ce constat rend essentiel le developpement d'outils economiques aptes a suivre en temps reel la physico-chimie des milieux aquatiques. La conception de moyens autonomes, rapides, fiables et precis adaptes aux mesures en continu, ouvre une voie innovante a l'evaluation des flux dans l'environnement. L'installation de micro-capteurs in situ repond a cette necessite. Ce sont des instruments installes en reseau aux points nevralgiques d'un systeme sous surveillance et mesurant en continu leur environnement physico-chimique. Les principes de detection ne semblent pas constituer un facteur limitant au developpement de tels micro-capteurs. Leur choix et developpement passent par un dialogue entre demandeurs de grandeurs physico-chimiques et fournisseurs de micro-capteurs environnementaux. Les verrous scientifiques et technologiques a lever pour aboutir a des reseaux de micro-capteurs operationnels sur le terrain sont plutot situes au niveau du transducteur et du transmetteur. Aussi, les principaux axes de progres des micro-capteurs sont situes dans les domaines : - Miniaturisation, par integration des differents modules sur une meme puce, conduisant a une baisse de l'energie consommee et semble avoir au moins sur les electrodes de conductivite un effet benefique sur la sensibilite ; - Robustesse et notamment la resistance aux conditions environnementales et a l'encrassage. Ce point n'est pas un objet de recherche aussi developpe que la detection et des percees devraient etre possibles (et sont meme souhaitees) ; - Communication, un reseau de micro-capteurs doit avoir la possibilite de se geo-localiser (en cas de perte notamment), verifier l'etat de ses communications et de son voisinage, valider la qualite de ses donnees avant leur transmission, alerter en cas de situation anormale ; - Autonomie a augmenter par la diminution de la consommation energetique ou developpement de possibilites d'alimentation in situ (les biopiles pourraient etre une voie a explorer) ; - l'Eco-conception doit etre integree des le choix du principe de mesure. Dans l'eventualite de perte dans l'environnement, la constitution du micro-capteurs doit bannir l'utilisation de substances toxiques ou dangereuses pour l'environnement (notion de cycle de vie du micro-capteur a integrer). Enfin il convient de mentionner la necessite de developper les technologies de l'information et de la communication (TIC) dans le but de gerer les flux de donnees generes par un reseau de micro-capteurs de facon optimale.

A Hg(II) conductometric sensor based on mercaptostyrenedivinylbenzene resin as ion-exchange material was prepared by the incorporation of this resin in a PVC membrane (proportions of resin, PVC and plasticizer being 10/33/67). The sensor gives a response in the concentration range 10(-3) M to 10(-10) M and the detection limit for Hg(II) ions is 10(-10) M. This sensor operates well in the pH range of 6-7 and in 0.1 mM phosphate buffer and it can detect mercury at this range of temperature (0 degrees C-70 degrees C). The sensor exhibits high selectivity towards mercury(II) ions versus different heavy metal ions.

This article describes a conductometric bi-layer based bienzyme biosensor for the detection of proteins as a marker of organic matter in rivers. Proteins were chosen to be used as indicators of urban pollution. The working mechanism of the bienzyme biosensor is based on the enzymatic hydrolysis of proteins into several fractions (peptides and amino acids), which results in a local conductivity change depending of the concentration of proteins. In this work, we began with the optimization of biosensor response using bovine serum albumin (BSA) as standard protein. For this objective seven enzymatic biosensors were prepared: four enzymatic sensors with only one layer of enzyme (proteinase K, trypsin, pronase or protease X) and three other enzymatic sensors with two layers (first layer: membrane containing proteinase K; second layer: one of the three other enzymes: trypsin, pronase or protease X). The biosensors were obtained through the deposition of enzymatic layers and the cross-linking process between enzymes and BSA in saturated glutaraldehyde vapour. The response of the various biosensors, described previously, were compared with the values of total organic carbon (TOC), and those of organic nitrogen (Norg), as determined by the laboratory accredits (CEMAGREF of Lyon) using the traditional method of analysis (NF EN 1484, infrared spectroscopy) and (NF EN 25663, mineralization/colorimetry assay) respectively for each water sample obtained from different sites in Lyon (France). The linear correlations obtained with the response of the seven biosensors showed the most important indices of correlations for the biosensor with two enzymatic layers: proteinase K + pronase (pkp). The optimum conditions for the preparation of the pkp biosensor increased the sensitivity and gave a limit of quantification of 0.583 μg/L for TOC and 0.218 μg/L for Norg in water samples. This sensor shows good reproducibility (2.28%), a capacity to be used at temperatures range 10–30°C (depending on the season) and moreover a long lifetime (5 weeks).

In this work chemiluminescence (CL) of luminol was used for the determination of Co(II). This method is based on the fact that Co(II) catalyzes the CL reaction of luminol in the presence of H2O2. The optimization of the conditions of CL measurements in a liquid system (effect of luminol and H2O2 concentrations) is studied. This method has shown a remarkable sensitivity until 4 fg/L of Co(II) as detection limit. The linear range extends from 0.4 pg/L to 40 mu g/L of Co(II). The optimum conditions for the preparation of the chitosan membranes for the adsorption of cobalt ions were studied. The analytical characteristics of the membrane/liquid CL system are similar to those of the CL liquid system. The preconcentration of cobalt ions on the chitosan membrane presented here opens up possibilities for a number of biomedical applications for determination of Vitamin B-12 containing a cobalt ion in pharmaceuticals, human serum, egg yolk and fish tissue, and for environmental applications for the detection of cobalt in soils and river waters.

In this paper, two technologies (Photolithographic and Laser) and three designs of interdigitated electrodes (Simple IDT Assymetric Branching IDT and Branching IDT) were compared for simple conductivity measurements of saline solutions (NaCl) and for enzymatic detection of protein (Bovine Serum Albumin). The results of both tests, showed that the Assymetric Branching IDT is the most sensitive in comparison to other electrodes, its sensitivity is 1.5 higher than that of simple IDT for conductivity measurements and 2.2 higher for protein detection. Moreover, the "laser" electrodes present a remarkable reproducibility in comparison to the "photolithographic" electrodes.

This work presents a new sensor for ammonium determination based on interdigitated conductometric thin-film planar electrodes. It was fabricated by including nonactin in a plasticised poly(vinyl chloride) membrane deposited on the sensitive area of the transducer. The effects of pH, buffer concentration, the interferences of Na+, K+ and Ca2+ ions, the effect of ionic strength and of temperature were investigated. The linear working range and sensitivity of the biosensor were also determined. The sensitivity of the ammonium detection was around 6.2 µS µM−1 and the detection limit was 2 × 10−5 M. The biosensor exhibits the advantages of a simple fabrication procedure, good sensor-to-sensor reproducibility, wide dynamic range and good storage stability (12 weeks).

A highly sensitive, fast, and stable conductometric enzyme biosensor for the determination of nitrate in water is described and validated in natural water samples. The nitrate biosensor is based oil a methyl viologen mediator mixed with nitrate reductase (NR) from Aspergillus niger and Nafion (R) cation-exchange polymer dissolved in a plasticized PVC membrane deposited oil the sensitive surface of interdigitated electrodes. The process parameters for the fabrication of the enzyme biosensor and various measuring conditions such as pH buffer concentration and temperature were investigated with regard to their effect on sensitivity, limit of detection, dynamic range and operational and storage stabilities. The sensitivity of the nitrate sensor was approximately 1.48 mu S.L/mg, the detection limit was 1.2 mu g/L, and linear calibration was in the range from 4x10(-3) to 8 mg/L with an application domain from 4x10(-3) to 50 mg/L. When stored in 20 mM phosphate buffer (pH 7.5) at 4 degrees C, the sensor showed good stability over 2 months.