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A low-cost disposable lipase activity sensor was developed and characterized overcoming the main drawbacks of the already existing disposable ones: insufficient reproducibility to be applied for automatic lipase activity quantification and complicated and long manual analytical procedure performed by qualified personnel. The sensor is based on a capacitor formation on an electrode surface by a substrate layer deposition possessing high electrical resistivity and dielectric constant (composite of olive oil mixed with BaTiO3 nanoparticles) serving as both: sensor sensitive layer and capacitor dielectric. Its decomposition by lipase catalyzed hydrolysis causes its thickness decrease resulting in capacitance increase proportional to the lipase activity. The sensor was characterized in terms of limit of quantification, linear quantification range, sensitivity, response time, precision, repeatability, storage time and the results are presented and discussed. The validation experiment showed excellent agreement with the standardized titrimetric method.

The present work discusses the problem of induced external electrical noise as well as its removal from the electrical potential obtained from Scanning Vibrating Electrode Technique (SVET) in the pitting corrosion process of aluminum alloy A96061 in 3.5% NaCl. An accessible and efficient solution of this problem is presented with the use of virtual instrumentation (VI), embedded systems, and the discrete wavelet transform (DWT). The DWT is a computational algorithm for digital processing that allows obtaining electrical noise with Signal to Noise Ratio (SNR) superior to those obtained with Lock-In Amplifier equipment. The results show that DWT and the threshold method are efficient and powerful alternatives to carry out electrical measurements of potential signals from localized corrosion processes measured by SVET., The authors acknowledge the Materials Corrosion Laboratory of the UABC Institute of Engineering for the economic support and facilities provided for the development of electronic instrumentation and testing of the experimental processes. They are grateful for the international collaboration with the National Center of Metallurgical Research (CENIM) Madrid, the Spanish State Council for Scientific Research (CSIC), for the support provided in the research and experimentation process in this work.

La industria electrónica ha crecido en los últimos cincuenta años, sobre todo en los países desarrollados, contribuyendo a su progreso económico. Particularmente en el Estado de Baja California ubicada en el noroeste de México, estas empresas han prosperado en los parques industriales de Mexicali considerada como una zona árida y Ensenada, un puerto y ciudad en el Océano Pacífico, que es una región marina. En ambos ambientes, durante el invierno y el verano los principales factores climáticos en ambientes de interiores son la humedad y temperatura, que aunados a los contaminantes del aire generan corrosión en dispositivos y equipos electrónicos, disminuyendo su rendimiento operativo. El cambio de clima en interiores de plantas industriales se debe a la variación de humedad, temperatura, radiación solar, así como a la concentración de contaminantes atmosféricos como el CO, SO2, H2S, NOX, O3 y partículas sólidas PM2.5 y PM10 provenientes de exteriores de la industria electrónica. Los gases y partículas contaminantes del aire son detectados por Estaciones de Monitoreo Ambiental (EMA) en Mexicali, mientras, que el SOX y Cl- se determinaron en Ensenada por la técnica de platos de sulfatación (TPS) y el método de la vela húmeda (MVH). Las probetas metálicas en ambas ciudades fueron analizadas por microscopia de barrido por electrones (MBE) y espectroscopia de electrones Auger (EEA) para determinar los productos de corrosión. Los equipos electrónicos instalados en las plantas están constituidos por componentes de cobre, siendo un metal muy utilizado por su buena conductividad eléctrica y térmica. Debido a que están expuestos a una amplia gama de ambientes agresivos, se origina deterioro del cobre, generando fallas en los equipos y con ello pérdidas económicas. Los materiales metálicos utilizados en los dispositivos electrónicos son susceptibles a la corrosión en interiores de plantas industriales por la variaciones de humedad y temperatura que generan el tiempo de humectación (TH), originando formación de una película delgada de agua sobre la superficie metálica, además de la exposición principalmente de sulfuros en Mexicali y cloruros en Ensenada, generan el proceso de corrosión.

Hydrogen sulphide (H2S) is considered one of the most corrosive atmospheric pollutants. It is a weak, diprotic, reducing acid, readily soluble in water and dispersed into the air by winds when emitted from natural, industrial, and anthropogenic sources. It is a pollutant with a high level of toxicity impairing human health and the environment quality. It attacks copper forming thin films of metallic sulphides or dendrite whiskers, which are cathodic to the metal substrate, enhancing corrosion. H2S is actively involved in microbially influenced corrosion (MIC) which develops in water, involving sulphur based bacteria, in oxidizing and reducing chemical reactions. H2S is found in concentrated geothermal brines, in the atmosphere of geothermal fields, and in municipal sewage systems. Other active atmospheric pollutants include SOX, NOX, and CO. This investigation reports on the effects of H2S on copper in microelectronic components of equipment and devices, with the formation of nonconductive films that lead to electrical failures.

The microelectronic industry applies materials with good electrical and corrosion resistance properties for the manufacturing of the microelectronic devices. Silver and copper are materials with this characteristics used for that purpose. Some of their main applications are as high thermal conductive die attach paste that had silver flakes as conductive filler material, silver plated over copper frames, Sn-Ag and Sn-Cu alloys for solder paste used in Surface Mount Technology (SMT) process, conductive internal copper layers in printed circuit boards, copper wire bonding, and more. Other metals and alloys, widely used for support frames, heat diffusers and case wares in the electronics industry are tin, nickel, aluminum, carbon steel and galvanized steel.

The electrochemical biosensors are analytical devices designed by coupling biological recognition elements and electrochemical transducers. The transducer converts the analytical signal produced as a result of the biochemical and electrochemical interactions into measurable electrical one (Thevenot et al., 1999). The electrochemical biosensors are self-contained, simple to handle, and able to provide specific, sensitive, accurate and cost-effective in situ and on line measurements in real time, without or with a minimum sample preparation. Because of these advantages over the conventional analytical methods, they are well suited for the detection of a large spectrum of compounds, entering food and subjects of analytical control. The present work is intended to demonstrate the applicability of the electrochemical biosensors for arsenic determination in beverages.

In this work is reported a rapid and sensitive electrochemical method for trypsin activity determination, based on the use of a gelatin coated glassy carbon electrode and registration of the current of hydroquinone oxidation depending on trypsin activity. The hydrogel film creates a kinetic barrier for the transport of the electroactive species to the electrode surface. The progressive trypsin catalyzed film digestion causes increase of its permeability, resulting in increase of the hydroquinone oxidation current. Current increase dependence on trypsin activity was investigated under various experimental conditions: hydrogel film thickness, hydroquinone solution concentration, and incubation time. Current response as a function of trypsin concentration within 10 min of incubation time was evaluated in the range of 0.1 to1000 μg mL-1. The limit of detection achieved in optimal conditions was found to be 0.01 μg L-1. The proposed approach allows trypsin sensing in the normal and acute pancreatitis range.

The organophosphorus (OP) pesticides are synthetic esters, amides, or thiol derivatives of the phosphoric, phosphonic, phosphorothioic, or phosphonothioic acids (Corbett et al., 1984; Eto, 1974; Gupta, 2006; Hassall, 1982; Quin, 2000). The structural diversity of this family of compounds is reflected in their physicochemical and biological properties: vapour pressure, solubility in water, chemical stability and toxicity (Corbett et al., 1984; Hassall, 1982; WHO, 1986), which determine their specific application (Hassal, 1982). Compared to the mostly banned in U.S. and Europe organochlorine pesticides, the OP ones are less persistent in the environment, are not subject of bioaccumulation and biomagnification, and do not release toxic break down products (Krieger, 2001). These features justify their application in the agricultural and veterinary practices of the modern world. In 1999 the OP insecticides represented ≈37% of the pesticides in use at a global scale (Table 1) and 72% of the insecticides used in U.S. (Kiely et al., 2004). The top ten OP insecticides active ingredients include malathion, chlorpyrifos, terbufos, diazinon, methyl-parathion, phorate, acephate, phosmet, azinphos-methyl, and dimethoate (Kiely et al., 2004).

The purpose of this paper is to evaluate the electrochemical behaviour of corrosion inhibition of the copper-carbon steel galvanic couple (Cu-CS), exposed to reverse osmosis water (RO) used for rinsing of heat exchangers for heavy duty machinery, during manufacture. Molybdate and nitrite salts were utilized to evaluate the inhibition behaviour under galvanic couple conditions. Cu-CS couple was used as working electrodes to measure open circuit potential (OCP), potentiodynamic polarization (PP), and electrochemical impedance spectroscopy (EIS). The surface conditions were characterized by scanning electron microscopy (SEM) and electron dispersive X-ray spectroscopy (EDS). The most effective concentration ratio between molybdate and nitrite corrosion inhibitors was determined. The morphological study indicated molybdate deposition on the anodic sites of the galvanic couple. The design of molybdate-based corrosion inhibitor developed in the present work should be applied to control galvanic corrosion of the Cu-CS couple during cleaning in the manufacture of heat exchangers.

The goal of this work is the evaluation of the analytical characteristics of the determinations performed using glucose oxidase and acetylcholinesterase based electrochemical sensors, developed applying original or optimized conventional methods of enzyme immobilization. It was found that the sensitivity of glucose determination, for example, varies from 0.048 to 3.36 mA L mol -1 cm -2 and the response time of the glucose oxidase based sensors – from 5 to 30 s, according to the method of the bioreceptor immobilization. The sensitivity of the analysis is affected from the activity of the immobilized biocomponent, from the composition of the solution (concentration of the substrate, of the mediator and of the inhibitor), and from the experimental conditions (pH, temperature, agitation), as well as from the kinetic parameters of the studied process. It was found that the immobilized glucose oxidase conserves its substrate specificity in the presence of a number of glucides (galactose, maltose, fructose, and saccharose) in 100 fold higher concentrations. The selectivity of glucose analysis is ensured applying a suitable potential. Interferences free glucose amperometric determination was performed at 0.00 V/SCE, in the presence of ascorbates and urates. The electrochemical quantification of enzyme inhibitors allows reaching particularly low limits of detection (10 -9 -10 -14 mol L -1 ).

International audience; The photosynthetic bacterium, Rhodobacter capsulatus, produces hydrogen under nitrogen-limited, anaerobic, photosynthetic culture conditions, using various carbon substrates. In the present study, the relationship between light intensity and hydrogen production has been modelled in order to predict both the rate of hydrogen production and the amount of hydrogen produced at a given time during batch cultures of R. capsulatus.The experimental data were obtained by investigating the effect of different light intensities (6000-50,000 lux) on hydrogen-producing cultures of R. capsulatus grown in a batch photobioreactor, using lactate as carbon and hydrogen source. The rate of hydrogen production increased with increasing light intensity in a manner that was described by a static Baly model, modified to include the square of the light intensity. In agreement with previous studies, the kinetics of substrate utilization and growth of R. capsulatus was represented by the classical Monod or Michaelis-Menten model. When combined with a dynamic Leudekong-Piret model, the amount of hydrogen produced as a function of time was effectively predicted. These results will be useful for the automatization and control of bioprocesses for the photoproduction of hydrogen.

A modification of the voltammetric technique Differential Alternative Pulses Voltammetry (DAPV) reported by the authors earlier (1) is presented. The potential-time waveform and the signal processing algorithm were properly modified allowing the performance of the DAPV in anodic stripping mode (ASDAPV). These improvements allow its application for trace species determinations in multicomponent solutions without preliminary extraction and separations procedures. Examples of the application of ASDAPV for direct simultaneous determinations of couples of ions having small E1/2 difference as well as for simultaneous multicomponent determinations are presented and discussed.

International audience; A new voltammetric technique providing high resolution – Differential Alternative Pulses Voltammetry (DAPV) based on the nonlinearity of I/E characteristic of the electrochemical systems was developed, suitable for simultaneous determination of species without their preliminary separation. Superimposition of couples of single rectangular pulses separated by a constant delay time and having same amplitude and opposite polarity, combined with appropriate signal processing yields first derivative of peak shaped curve. The DAPV faradaic current response equation for reversible electrochemical reactions was theoretically derived, graphically presented and experimentally tested. DAPV was applied for determination of species having very near E1/2 potentials: Pb2+/Tl+ and In3+/Cd2+ under increasing concentration ratios. The experimental results compared with those obtained by Differential Pulse Polarography (DPP) and Second Harmonic Alternating Current Polarography show superiority of DAPV resolution power which is combined with high sensitivity, similar to that providing by DPP, employing a simple electronic equipment.

International audience; The sensors applied recently for determination of cholinesterase activity are mostly enzymatic amperometric sensors, in spite of their disadvantages: short life-time at ambient temperature, instability of the response, interferences, as well as passivation of the electrode surface. In the present paper a new approach for determination of cholinesterase activity was proposed, overcoming the main drawbacks of the analysis performed with amperometric enzymatic sensors. Instead of the immobilization of enzymes on a conducting electrode surface, whole cells of Arthrobacter globiformis, containing choline oxidase were fixed on a Clark type oxygen probe. Current proportional to bacteria respiration is registered as a sensor response. The application of whole cells of bacteria as a sensing element permits to achieve high stability of the response and long life-time of the sensor at ambient temperature, due to the conservation of the enzyme in its natural micro-environment inside the immobilized cells. The proposed sensor keeps its functionality more than 7 weeks stored in deionized water at ambient temperature. For the first 2 weeks the amplitude of the response decreases with only 10% and at the end of the studied 7 weeks period the response was 50% of the initial. The other advantages of the proposed sensor are: the dissolved oxygen is used as a mediator which concentration can be reliably and interferences free measured by the aim of a Clark type oxygen probe applied as a transducer; reproducible bacterial membranes can be elaborated by filtration of resuspended bacterial culture after preliminary determination of its activity; application of membranes containing lyophilized bacteria capable to be conserved infinitely long time and activated just before their application; negligible cost compared with the sensors based on immobilized enzymes. The steady-state response of the proposed bacterial sensor to choline obtained in 200 s is linear in the investigated concentration range up to 2 × 10–4 mol dm–3, with detection limit of 8 × 10–8 mol dm–3 and sensitivity of 4 × 10–1 μA cm3 mol–1, at pH 6, temperature of 25 °C and stirring rate of 300 rpm. Choline is formed as a result of the catalytic hydrolysis (depending on the cholinesterase activity) of the substrate acetylcholine. Linear calibration graph for cholinesterase activity determination was obtained in the range up to 11 mU cm–3, with a slope of 1.97 × 10–2 μA cm3 mU–1, at pH 6, temperature of 25 °C and stirring rate of 300 rpm. The tests with reconstituted lyophilized serum with known activity used as a control sample confirm the accuracy of the proposed method. The relative error of the determination was only 2.82%.

International audience; The adsorption (fixation) of bacteria Acidithiobacillus ferrooxidans on Hg and Cu metallic surfaces was qualitatively studied owing to two independent methods: frequency measurement using a quartz crystal microbalance and light absorption measuring at the Hg/bacterial culture interface. A method using a dropping mercury electrode (DME) allowed quantifying this bacterial fixation. Determining the superficial tension at Hg/bacterial culture interface led to determine bacteria adsorption on Hg through the Gibbs isotherm. A modified stripping voltammetry was proposed taking benefit of both bacterial adsorption on Hg surface and metal fixation capacity on biomass. Metal preconcentration on the biologically modified Hg electrode appeared to improve the measurement sensitivity of differential pulse anodic stripping voltammetry (DPASV). The height of the detected peaks was thus increased of 17.6% for copper, 48.4% for lead, and 132% for cadmium determinations compared to those obtained with an unmodified mercury electrode. Such augmentation depended on bulk bacteria concentration and bacteria preconcentration.