Showing papers in "Sensors in 2001"

New Trends in Biosensors for Organophosphorus Pesticides

Abstract: Biosensors are sensitive and can be used as disposable sensors for environmental control These biosensors are based either on inhibition of acyl cholinesterases acetylcholinesterase or butyrylcholinesterase) by organophosphorus compounds or on inhibition of enzymes phosphatases (acid or alkaline) or on direct detection of organophosphorus compounds by organophosphorus hydrolase The state-of-the-art of the three types of biosensors will be presented in this paper and a particular development will be done on our work on ENFET (Enzymatic Field Effect Transistor) biosensors

Electrochemical Metal Ion Sensors. Exploiting Amino Acids and Peptides as Recognition Elements

Abstract: Amino acids and peptides are known to bind metal ions, in some cases very strongly There are only a few examples of exploiting this binding in sensors The review covers the current literature on the interaction of peptides and metals and the electrochemistry of bound metal ions Peptides may be covalently attached to surfaces Of particular interest is the attachment to gold via sulfur linkages Sulfur-containing peptides (eg cysteine) may be adsorbed directly, while any amino group can be covalently attached to a carboxylic acid-terminated thiol Once at a surface, the possibility for using the attached peptide as a sensor for metal ions becomes realised Results from the authors’ laboratory and elsewhere have shown the potential for selective monitoring of metal ions at ppt levels Examples of the use of poly-aspartic acid and the copper binding peptide Gly-Gly-His for detecting copper ions are given

A Carbon Nanotube-based Sensor for CO2 Monitoring

Abstract: A carbon dioxide (CO2) sensor is fabricated by depositing a thin layer of a multiwall carbon nanotube (MWNT) – silicon dioxide (SiO2) composite upon a planar inductorcapacitor resonant circuit. By tracking the resonant frequency of the sensor the complex permittivity of the coating material can be determined. It is shown that the permittivity of MWNTs changes linearly in response to CO2 concentration, enabling monitoring of ambient CO2 levels. The passive sensor is remotely monitored with a loop antenna, enabling measurements from within opaque, sealed containers. Experimental results show the response of the sensor is linear, reversible with no hysteresis between increasing and decreasing CO2 concentrations, and with a response time of approximately 45 s. An array of three such sensors, comprised of an uncoated, SiO2 coated, and a MWNT-SiO2 coated sensors is used to self-calibrate the measurement for operation in a variable humidity and temperature environment. Using the sensor array CO2 levels can be measured in a variable humidity and temperature environment to a ± 3% accuracy.

Choosing a Humidity Sensor: A Review of Three Technologies This discussion of the operating principles of capacitive, resisitive, and thermal conductivity humidity sensors also addresses their advantages, disadvantages, and applications

Abstract: Additional significant long-term factors are the costs associated with sensor replacement, field and in-house calibrations, and the complexity and reliability of the signal conditioning and data acquisition (DA) circuitry. For all these considerations to make sense, the prospective user needs an understanding of the most widely used types of humidity sensors and the general trend of their expected performance. Definitions of absolute humidity, dew point, and relative humidity are provided in the sidebar, \"Humidity Basics\").

Improving the Responses of Several Accelerometers Used in a Car Under Performance Tests by Using Kalman Filtering

Abstract: In this paper a Kalman filter is used to cancel noise and interference contained in two accelerometers embedded in a car under performance tests. Here, the frequency bands of the signals of interest and their noise (deterministic as well as stochastic) are not strongly mixed with each other but it is very difficult to diminish the noise by using the classical approach to filtering. This reason, among others, justifies the necessity of the application of optimal filtering; and the Kalman filtering application allowed us to obtain optimal results (in the minimum mean-square sense) and signal-to-noise ratio improvements higher than 30 dB were achieved. The experimental results demonstrate the importance of using both analog signal conditioning and digital signal processing when dealing with signals corrupted by noise.

Errors in Chemical Sensor Measurements

Abstract: Various types of errors during the measurements of ion-selective electrodes, ionsensitive field effect transistors, and fibre optic chemical sensors are described. The errors were divided according to their nature and place of origin into chemical, instrumental and non-chemical. The influence of interfering ions, leakage of the membrane components, liquid junction potential as well as sensor wiring, ambient light and temperature is presented.

Dynamic Rotary Torque Measurement Using Surface Acoustic Waves

Abstract: This paper identifies a new, potentially low cost, non-contact, frequency domain strain torque sensor utilising SAW (Surface Acoustic Wave) Technology for surface strain measurement. The sensor has a short axial length making it flexible in terms of integration into a variety of applications, encompassing both static and dynamic measurement. The paper presents a technical description of the resulting transducer, regarding its operation and construction.

An Optical Biosensor for Monitoring Antigen Recognition Based on Surface Plasmon Resonance Using Avidin-Biotin System

Abstract: Author to whom correspondence should be addressed. Tel/Fax: +86-431-8922161.E-mail: qhjin@public.cc.jl.cnReceived: 21 July 2001 / Revised: 29 July 2001 / Accepted: 07 August 2001 Published: 12 August 2001Abstract: A novel optical biosensor based on simultaneous multiwave length detectionsurface plasmon resonance (SPR) has been developed for immunosensing. The sensor isdesigned on the basis of fixing angle of incidence and measuring the reflected intensities oflight in the wavelength range of 400–800 nm. The SPR spectra are shown in terms ofreflected light intensity verus wavelength of incident light. The intensity of the reflectedlight is the minimum at the resonant wavelength. The biorecognition surface, formed on achemically modified gold layer, consists of avidin that is specifically bound with biotin.These sensing membranes were self-assembled on gold layer. The processes of sensingmonolayer formation were studied in real time through observing the change of resonantwavelength. The modified surface was used as a model immunosensor and to detectsuccessfully the human factor B (Bf). The Bf was determined in the concentration range of0.5~100 µg/mL. Under optimum experimental conditions, the sensor has a goodrepeatability, reversibility and selectivity.Keywords: Surface plasmon resonance, Biosensor, Avidin, Biotin

Magnetism-Based Remote Query Glucose Sensors

Abstract: Two wireless, passive remote query magnetism-based glucose sensors, which operate in combination with a mass and volume changing glucose responsive polymer, are presented. One sensor design is based upon the magnetostatic coupling of magnetically soft thin-film elements; as the polymer volume changes in response to glucose concentration so does the magnetostatic coupling between elements. In response to a time varying magnetic field, upon reversal of the magnetization vector of the elements the magnetostatic coupling determines the time rate of change of magnetic flux, and hence the amplitude of the voltage spike generated in a pick-up coil. The other sensor consists of a free-standing magnetoelastic thick-film, coated with a thin layer of the glucose responsive polymer. In response to a time varying magnetic field the sensor mechanically vibrates at a characteristic resonant frequency; the characteristic resonant frequency of the sensor linearly tracks the change in mass of the glucose responsive polymer.

A „Hybrid“ Thin-Film pH Sensor with Integrated Thick-Film Reference

Abstract: New Mexico State University, Las Cruces, NM 88003-8001, USA* Author to whom correspondence should be addressed.Received: 28 September 2001 / Accepted: 10 October 2001 / Published: 2 November 2001Abstract: A reference electrode fabricated by means of thick-film technique is depositedonto a silicon substrate and combined with a thin-film pH sensor to a “hybrid” chip system.To evaluate the suitability of this combination, first investigations were carried out. Thecharacteristics of the thin-film pH sensor were studied towards the thick-film Ag/AgClreference electrode. Measurements were performed in the capacitance/voltage (C/V) andconstant capacitance (Concap) mode for different pH values keeping the concentration ofchloride ions constant. No difference of the sensor behaviour could be found whencomparing the results to measurements, obtained versus a conventional macroscopicAg/AgCl reference electrode.Keywords: Hybrid sensor chip, Thick-film reference electrode, Thin-film pH sensor.IntroductionThe requirement of continuous monitoring for environmental and medical applications has beentaken place in a main interest of developing a variety of miniaturised sensors for chemical andbiological analytes in aqueous solutions [1-7]. In combination with the possibility of using siliconplanar technology, some miniaturised potentiometric sensors have been developed and are nowavailable [8]. The advantage of such sensors is their process compatibility with integrated circuittechnology. Furthermore, they are appropriate for on-line monitoring, where small analyte volumes areneeded. However, these miniaturised sensors still suffer from the drawback of an integrated reference

Design a Low-Jitter Clock for High-Speed A/D Converters

Abstract: High-speed applications using ultra-fast data converters in their design often require an extremely clean clock signal to make sure an external clock source does not contribute undesired noise to the overal dynamic performance of the system. It is therefore crucial to select suitable system components, which help generate a low phase-jitter clock. The following application note serves as a valuable guide for selecting the appropriate components to design a low-phase noise PLL-based clock generator, suitable for ultra-fast data converters.

The New Theory of Ion-Selective Electrodes

Abstract: The paper discusses the anomalies of the former interpretation of the working mechanism of ion-selective electrodes. It was thoroughly discussed why the Donnan experiment could not be applied as the theoretical background of glass electrodes. It was assumed according to the Donnan interpretation that the measurable potential is produced by the transfer of the primary ion through the membrane. Since the 1960s, the author and coworkers have been investigating the problem of what can be the reason for the potential response of the electrodes. Practical measurements in connection with the response time, surface hindered reactions etc. were interpreted. Furthermore, the energy problems according to the Gibbs theory using two electrode components were investigated. It was established that the electrodes on which chemical reactions may occur with the primary ion have a surface reaction as the chemical basis of the response. For electrodes that work on the principle of the lyotropic series, surface reactions are also involved, but their response is not always Nernstian. The energy demand is covered by the charge separation at the electrode ‐solution interface.

Assembly method fabricating linkers for covalently bonding DNA on glass surface

Abstract: A fabrication method of linkers to covalently anchor nucleic acid probes (such as, oligonucleotides, PCR-products or peptide nucleic acid oligomers) on glass was developed by alternatively covalently assembling the different molecular components. The linkers with controllable length, flexibility and hydrophilicity could be prepared simply by dipping subtracts alternatively in different chemical solutions. A dialkoxy aminosilane (N-(2-aminoethyl)-3-aminopropylmethyl dimethoxylsilane, AEAPS) was chosen to substitute common used trialkoxy aminosilane to modify glass surface. The end groups of the linkers were formed as aldehyde or amino group, which were successfully used for attaching prefabricated DNA or in situ synthesis of oligonucleotides, respectively. The both experiments showed that the linker produce good reproducibility and uniformity of fluorescent hybridizing images, which can distinguish an internal single base mismatch in 20mer oligonucleotides.

Sensors and Asymptotic w-observer for Distributed Diffusion Systems

Abstract: The aim of this paper is to study the regional observer concept through the consideration of sensors. For a class of distributed diffusion systems, we propose an approach derived from the Luenberger observer type as introduced by Gressang and Lamont [1]. Furthermore, we show that the structures of sensors allow the existence of regional observer and we give a sufficient condition for each regional observer. We also show that, there exists a dynamical system for diffusion systems is not observer in the usual sense, but it may be regional observer.

Sulfonated Polyaniline Coated Mercury Film Electrodes for Voltammetric Analysis of Metals in Water

Abstract: Denise Alves FungaroInstitute for Energy and Nuclear Research – Center of Environmental Chemistry - Travessa R, 400 -CEP 05508-900 - Sao Paulo, SP, Brazil E-mail: dfungaro@netipenbrReceived: 19 November 2001 / Accepted: 26 November 2001 / Published: 26 November 2001Abstract: The electrochemical polymerization of 2-aminobenzenesulfonic acid with andwithout aniline has been carried by cyclic potencial sweep in sulfuric acid solution at theglassy carbon electrode The polymer and copolymer formed have been characterizedvoltammetrically The sulfonated polyaniline coated mercury thin-film electrodes have beenevaluated for use with anodic stripping voltammetry The electrodes were tested andcompared with a conventional thin-film mercury electrode Calibration plots showedlinearity up to 10

Nafion Coated Electrodes as Voltammetric Sensors for Iron Analysis in Sediments and Pore Waters: an Example from the Lagoon of Venice

Abstract: Glassy carbon electrodes coated with Nafion are used for the ion-exchangevoltammetric (IEV) determination of Fe(II) in the pore-waters and acidic extracts ofsediments of the lagoon of Venice (Italy). The coated electrodes give reversiblevoltammetric signals, well resolved from background currents, which can be used forquantitative determinations. The yield of iron extracted by HCl from the sediment dependson the experimental conditions, in particular on the concentration of hydrochloric acid. Bycombining IEV on the acid extract with trapping and analysis of gaseous H 2 S evolved it ispossible to obtain quantitative information both on the total content of iron dissolved by theacid attack and on the fraction of iron present in the form of acid volatile sulphides (AVS).As far as pore-waters are concerned, in this kind of samples the IEV determination of ironcan be performed simply after dilution with HCl. The pore-waters here examined weresampled without alteration of their equilibrium conditions by using a suitable “in situ”sampler.IEV data obtained in samples from the lagoon of Venice (Italy) show satisfactory correlationwith previous results obtained using different analytical techniques.

Electrochemical Characterisation and Application of Multi Microelectrode Array Devices to Biological Electrochemistry

Abstract: A new design for microelectrode array (MEA) devices fabricated by semiconductor-processing techniques is presented. The microelectrode surfaces consist of gold and are surrounded by an insulating silicon nitride layer. Each chip of these so-called Multi MEAs contains regular arrays with circular-shaped electrodes of eight different sizes: 1, 3, 5, 10, 50, 100, 500 and 1000μm. The Multi MEAs were electrochemically characterised by use of ferrocenecarboxylic acid. Well-defined cyclic voltammograms of the two small redox proteins, horse heart cytochrome c and amicyanin from Thiobacillus versutus, were obtained at variously surface-modified Multi MEAs. Furthermore, a very simple method to manufacture Multi MEAs with carbon surfaces is introduced.

Mediated Electron Transfer at Redox Active Monolayers

Abstract: A theoretical model describing the transport and kinetic processes involved in heterogeneous redox catalysis of solution phase reactants at electrode surfaces coated with redox active monolayers is presented. Although the analysis presented has quite general applicability, a specific focus of the paper is concerned with the idea that redox active monolayers can be used to model an ensemble of individual molecular nanoelectrodes. Three possible rate determining steps are considered: heterogeneous electron transfer between immobilized mediator and support electrode ; bimolecular chemical reaction between redox mediator and reactant species in the solution phase, and diffusional mass transport of reactant in solution. A general expression for the steady state reaction flux is derived which is valid for any degree of reversibility of both the heterogeneous electron transfer reaction involving immobilized mediator species and of the bimolecular cross exchange reaction between immobilized mediator and solution phase reactant. The influence of reactant transport in solution is also specifically considered. Simplified analytical expressions for the net reaction flux are derived for experimentally reasonable situations and a kinetic case diagram is constructed outlining the relationships between the various approximate solutions. The theory enables simple diagnostic plots to be constructed which can be used to analyse experimental data.

Affinity sensors in non-equilibrium conditions: highly selective chemosensing by means of low selective chemosensors

Abstract: The selectivity of measurements by means of affinity sensors in (quasi)equilibrium conditions and in non-equilibrium conditions was compared. The results show that the measurements in non-equilibrium conditions can reduce or even eliminate a relative contribution of interferents to a sensor signal.

Evaluation of Protein Adsorption on Chitosan Surfaces with Reflectometry Interference Spectroscopy

Abstract: Using a biomedical sensor setup RIfS we have investigated the kinetic behavior of human albumin (Alb), human fibrinogen (Fib), and human immunoglobulin G (IgG) adsorbed onto surfaces of chitosan. Polystyrene (PS) was used as the control material in this study. The optical thickness of three kinds of proteins measured by RIfS was related to their molecular dimensions and potential orientations on a film surface. According to the operation principle of RIfS and the molecular dimensions of three kinds of proteins, the adsorbed layers of proteins onto the surface of chitosan and PS was calculated by using a newly introduced equation. The microstructure of the chitosan and polystyrene film and the surfaces with adsorbed proteins were imaged by atomic force microscopy (AFM). With AFM analyses the lateral distribution of the protein molecules on surfaces have been recognized. The results show that the number of adsorbed layers of the three proteins on the surface of chitosan are 0.635 for Alb, 0.158 for Fib and 0.0967 for IgG, and of polystyrene are: 0.577 for IgG, 0.399 for Fib, 0.336 for Alb. This study confirmed that RIfS is a useful tool for the analysis of plasma proteins adsorbed on a surface of biomaterials. Results show that at first on the surface of chitosan film much more Alb than Fib was adsorbed which demonstrated that chitosan has a antithrombus function. Secondly, on the surface of chitosan film more Alb and less Fib were adsorbed than on the surface of PS film, which demonstrated that chitosan has a better blood compatibility than polystyrene. Thirdly, the calculated layer number of the three proteins indicated that on both chitosan and PS substrates monolayer coatings form.

Design and Manufacture of Automotive Pressure Sensors

Abstract: Design and manufacturing methodologies for automotive pressure sensors to create robust sensors for this demanding environment. Material property selection and circuit design principles are covered. Cost sensitive designs that meet the range of automotive specifications and requirements are discussed. Analyzing defective units and manufacturing fallout as a tool to improving the design and manufacturing process. Among the more challenging tasks undertaken by sensor designers is the design and manufacture of reliable, robust piezoresistive sensors for the automotive market. Through years of trial and error, these designers have developed practices and techniques that have proven useful again and again for automotive applications. To enlighten and inform those who work with this technology (which addresses the leading volume user for piezoresistive sensors), the following discussion discloses several tricks of the trade. As a rule, 80% of the final cost for a product is established in the first 20% of the design effort. Thus, understanding the necessary design practices beforehand can minimize cost and improve your success in designing robust PRT pressure sensors for the demanding automotive environment. If you've never designed such sensors before, the first task is to open the hood of a recent-model vehicle (your own, perhaps) and have a good look at the engine compartment. That nest of wires, hoses, connectors, and engine is one of the most severe environments a sensor can have. Consider the thermal shock to an engine-mounted sensor operating above 100°C and sprayed suddenly with slushy, salty water at 70mph. Other properties of this environment are just as severe: Temperature: -40°C to +125°C (to +150°C for engine-mounted sensors) Vibration: Severe to extreme Sensing Media: Fuels (mixed blends), oil, brake fluid, transmission fluid, noxious vapors, etc. External Media: Water and saltwater spray, oils, brake fluids, solvents, fuels, etc. Thermal Shock: High-temperature operation plus frequent cold-water splashing EMI: 2MHz to 2GHz radiated exposure at 200 volts per meter Sensors located within the passenger compartment have much less exposure to fluids and solvents but are subject to low temperatures, water, and EMI: Temperature: -40°C to +85°C Vibration: Reduced levels Sensing Media: Air typically External Media: Water spray Thermal Shock: Reduced rate of change EMI: 2MHz to 2GHz radiated exposure at 200 volts per meter For either environment, the sensor should have the following: Reliability: 100% operational, every time, all the time Lifetime: 10 to 15 years, sometimes expressed in terms of mileage (100,000 150, 000) as well Low Cost: Automotive is among the most cost-sensitive of markets