A simple technique has been applied to the development of a glucose amperometric sensor by electro polymerizing aniline on platinum coated working electrode. The carboxyl-reactive groups of glucose oxidase were entrapped into the conductive layer of polyaniline formed on the electrode. The modified electrodes have been investigated by cyclic voltammetry, single potential step chronoamperometry and optical microscopy. The functionality of the chemically modified electrode was demonstrated and has been obtained by applying recording the chronoamperometry in presence of glucose concentrations at a low constant voltage of 220 mV.

The purpose of the work is the development of a fully integrated platform for pesticides detection, to be used in food monitoring giving quantitative information on the organophosphate and carbamate pesticides. The sensor design, fabrication, and characterisation and the platform components and functioning will be presented.

The paper work has been focused on the technology development of an impedimetric microbiosensor array for pesticides detection. The microbiosensors array is containing six biosensor chips integrated into a microfluidic system providing all fluids for biosensors activation and inhibition, electrically connected to electronic modules for signal processing and data acquisition. The overall pesticides detection platform is connected into a portable apparatus of small dimensions, low energy consumption, easy to be manipulated, providing independent functioning of biosensors with data acquisition from each one. The microcontroller will memorise the data and is able to discard them on the PC via USB. The biosensor is based on miniaturized interdigitated electrodes and immobilized acetylcholinesteraze on top of them. The acetylcholinesteraze based sensors are designed to detect the organophosphoric and carbamates compounds from pesticides, measuring the impedance of the layer adjacent to the electrodes surface. All pesticides detection measurements are realized under the strict control of temperature and pH using a Platinum temperature sensor and a pH electrode, both integrated on the same chip with the biosensor. The response time is about 10 minutes.

The following paper describes the design and functions of a miniaturized integrated platform for optical and electrical monitoring of cell cultures and the necessary steps in the fabrication and testing of a silicon microchip Micro ElectroMechanical Systems (MEMS)-based technology for cell data recording, monitoring and stimulation. The silicon microchip consists of a MEMS machined device containing a shank of 240 μm width, 3 mm long and 50 μm thick and an enlarged area of 5 mm × 5 mm hosting the pads for electrical connections. Ten platinum electrodes and five sensors are placed on the shank and are connected with the external electronics through the pads. The sensors aim to monitor the pH, the temperature and the impedance of the cell culture. The electrodes are bidirectional and can be used both for electrical potential recording and stimulation of cells. The fabrication steps are presented, along with the electrical and optical characterization of the system. The target of the research is to develop a new and reconfigurable platform according to the particular applications needs, as a tool for the biologist, chemists and medical doctors working is the field of cell culture monitoring in terms of growth, maintenance conditions, reaction to electrical or chemical stimulation (drugs, toxicants, etc.). HaCaT (Immortalised Human Keratinocyte) cell culture has been used for demonstration purposes in order to provide information on the platform electrical and optical functions.

Typical blocking I-V characteristics are shown and analyzed for PN junctions exhibiting a breakdown region above 1000 V from commercial diodes and power MOSFETs. The leakage reverse current of PN junctions from commercial silicon devices available at this time has a flowing component at the semiconductor-passivant material interface around the junction edge.Part of the plotted experimental current-voltage characteristic fits to linear variation and deviation from this variation at higher applied voltage is attributed to non-controlled current flow in the interfacial layer, between the silicon and passivating material from the junction periphery. The thin interfacial layer including atomic layers both from the semiconductor and passivating dielectric material with fixed charges has imperfections resulted from the junction passivation process. For controlled-avalanche PN junctions no deviation from linear voltage dependence of the reverse current is possible until breakdown region practically at right knee appears. For other PN junctions deviation of the reverse current from linear variation results in a breakdown region with round knee and still with visible voltage dependence at current increase. Such soft breakdown region caused by the phenomena in the interfacial layer is exhibited at lower applied reverse voltage than the expected one for breakdown caused by charge carrier avalanche multiplication at the junction. Operation even for short in the soft breakdown region can lead to PN junction failure and for this reason, a maximum working permissible reverse voltage is specified in device data sheet with a value under the breakdown region. junction failure consists in significantly lower reverse voltage than the initial one or even electrical short-circuit caused by a spot of material degradation in the interfacial layer from the junction periphery. Operation of the controlled-avalanche diode in the breakdown region is possible only for single pulse of short duration and at junction temperature not higher than 175 degrees C. Above 150-175 degrees C even for controlled-avalanche diodes deviation from linear variation of the reverse current has been observed and soft breakdown region can appear before the expected avalanche breakdown. Device failure after operation in the breakdown region, caused by spot of material degradation at the junction periphery has occurred in such conditions. For high voltage commercial power MOSFETs operation in the avalanche breakdown region is limited to 150 degrees C. (C) 2010 Elsevier Ltd. All rights reserved.

The paper is presenting the development of a sensor system dedicated to monitor the environment of eukaryotic cells culture acting as biosensors for toxins detection. The system we are presenting is containing pH, and temperature sensors integrated into microfluidic channels.

The detection of organophosphoric insecticides, in a simple manner was made using impedimetric enzyme biosensors, which allow determination in sub-micromolar concentration ranges. This type of measurement applies for monitoring of biocatalytic reactions based on irreversible inhibition of the enzyme (acetylcholinesterase). The reaction involves generation of charged species, which leads to a global change in the ionic composition of the tested solution.Our work has been focused on the development of an impedimetric microsensor for direct detection of dichorvos, because this kind of biosensor presents a number of advantages such as: miniaturized electrodes based on gold thin film; easy production using standard microtechnology; low cost; no reference electrode required; no light sensitivity and differential mode measurements possibile allowing elimination of interferences. In addition, dichlorvos is targeted to be detected considering that the commonest poisoning today is due to: Methyl Parathion (metacid), Dichorvos (Nuvan), Zinc Phosphide and Aluminium Phosphide (Celphos). The biosensor with interdigitated electrodes and immobilized acetylcholinesteraze (AChE) measures the impedance of the layer adjacent to the electrode surface. The impedimetric measurement consists of determining the conductivity and capacitance of the solution between two interdigitated electrodes. The chemistry of deposited enzymatic layer (concentration, enzymatic activity measuring, deposition protocol), the immobilization technique for AChE, the fabrication technique and the electrical characteristiques of the enzymatic sensor have been studied. AChE immobilization was performed by ionic adsorption on polyethylenglycol (PEG) bio-polymeric substrate, by including in the gel. The functionalized electrodes deposited with biomaterial were inserted into the microfluidic channels and tested from electrical andmicrofluidic point of view, achieving the micro-bio integration. Insertion of electrolyte- - plus acetilcholine into the channels leads to activation of the enzyme and the measurements are realized under the strict control of temperature and pH. The response time is about 10 minutes.

Drain electrical characteristics for a 10 A and 400V MOS transistor have been measured and analyzed. At junction temperature as high as 200 degC and above this value, accentuated rise of the drain reverse (blocking) current takes place before the specified voltage of 400 V is reached, due to current leakage at the cells junction edge. Observed constant drain current, attributed to a primary diffusion current component is not undoubted evidence for the location of this current in the junction bulk. Similar behavior is observed when bias voltage below the threshold voltage is applied on the gate. Oxide-passivated junctions from bipolar devices may behave like those from MOSFETs at high temperature

The paper describes an in house made experimental set-up that measures the thermal conductivity in liquids on the basis of the transient hot wire method. The theoretical principle is firstly presented, and then our original experimental approach is described. The hardware as well as the software implementation of the measurement method reveals the simple design configuration of the measurement set-up that contains high performance inexpensive components. It is also simple to use and well suited for research laboratories, data being stored either in text, or in graphical files. Finally, based on experimental results, the measurement accuracy and sensibility performances are discussed and compared with other instruments in literature

The paper describes an in house made experimental set-up that measures the thermal conductivity of liquids. The measurement principle is based on the Transient Hot Wire Method. The theoretical bases of the measurement method are firstly presented, and then our original experimental implementation is described. The hardware as well as the software design reveals the simple configuration of the measurement set-up that contains high performance inexpensive components. It is also simple to use and well suited for research laboratories, data being stored either in text, or in graphical files. Finally, based on experimental results, the measurement accuracy and sensibility performances are discussed and compared with other instruments in literature.

Due to high level of the leakage reverse current, commercial power silicon diodes available at this time have no specification in the data sheets for operation above 200 degC junction temperature. An experimental method is presented to extract information about the uniformity of the reverse current flow over the silicon die area. The power diode with copper attached heat sink is placed in a hot chamber where the temperature is set, so that the level of reverse current to be enough for heat generation. For the same applied power dissipation at reverse and forward bias, the additional junction temperature increase is monitored by the level of reverse current or by the level of the forward current at constant voltage. Experiments have been performed on commercial silicon diode samples in metallic package. It has been found that the additional junction temperature increase is significantly different, when the same power dissipation is applied at reverse bias and then at forward bias voltage, with the device placed in hot chamber at 200degC or 250 degC, depending on the current level

The present work proposes a genetic algorithm (GA) based method for the optimization of geometrical parameters to obtain maximum heat transfer in a micro-channel structure. The works were directed to the specific problems related to thermal transfer performances of micro-cooling systems on chip. Silicon etched micro-channels and water as cooling fluid are considered in the analysis. The results are in good agreement with those in numerical simulations, analytical models, and experimental available data.

Examples of reverse (blocking) I-V characteristics for PN junctions from available commercial power diodes and thyristors are shown. The surface leakage component of the junction reverse current is the primary component for standard recovery junctions. For fast recovery junctions, a secondary surface leakage current at lower applied voltage, may dominate the bulk component towards the maximum working reverse voltage. At high operation temperature, the dissipated power corresponding to the surface current component induces uncontrolled junction temperature peaks. Reverse current instability due to these temperature peaks, leads to device catastrophic failure if operation beyond the temperature and voltage ratings specified in the data sheets is permitted. Further reduction of the level of reverse current on behalf of the surface component, enables reliable operation at junction temperature higher than the maximum specified value in the data sheets. Higher working reverse voltage reaching the breakdown voltage is also possible.

The aim of the paper is to provide experimental results and analysis relating to the failure mechanism of the junction at operation near or in the breakdown region of electrical characteristic.

The surface component of reverse current of operating power PN junctions at high temperature, is a source of power dissipation concentrated in a very thin layer at the junction periphery. The resulted heat in this thin layer is removed towards the heat sink only through the peripheral part of the semiconductor die area. Typical commercial rectifier diodes exhibiting surface leakage current are considered to illustrate non-uniform junction temperature distribution. At higher applied reverse voltage, the surface component of reverse current flows non-uniformly around the junction perimeter. It is shown that the thermal resistance for the heat transfer from the junction periphery is significant higher than the corresponding one for the heat removal from the junction bulk. A simple evaluation indicates that the temperature of local hot spots near the junction peripheral surface may be at least 10 /spl deg/C higher than in the junction bulk. Junction temperature peaks were observed by infrared imaging microscopy. Influence on device reliability is possible.