We introduce a fiber optical sensors which is capable of analyzing polycyclic aromatic hydrocarbons (PAHs) and monoaromatics like benzene, tolouene, xylene, and ethylbenzene. The compact system is based on laser-induced, time-resolved fluorescence emission spectroscopy. It uses a miniaturized all solid state laser which can be operated alternately at 266 nm and 355 nm. The excitation light is guided through an optical fiber to the sensor head. The fluorescence light is collected by 4 optical fibers, which are placed around the excitation fiber, and guided to a detector, which consists of a spectrograph, a gateable image intensifier and a CCD camera. Time resolved spectra are recorded by moving the gate relative to the laser pulse. The focus of our work is the analysis of water but preliminary results of soil analysis are also presented. Limits of detection have been demonstrated for 15 PAHs from the EPA- list in water and some important mono-aromatics. Additionally some typical applications are presented, i.e. detection of fuel in water and diesel in soil.

Integrated optical transducers for the detection of chemical and biochemical species and for optical measurements on bulk media are the subject of intense research effort. While many such sensors have been demonstrated in research laboratories worldwide, commercial exploitation of integrated optical sensors has proceeded slowly. Progress towards incorporating multiple-output sensors, based around the use of integrated optical Mach-Zehnder interferometers, into a robust and inexpensive instrument is described in this paper. A 1D CCD array is used to acquire the multiple outputs, resulting in ready alignment and a flexible approach to device reconfiguration and offering particular promise for application to multianalyte transducers where several signals must be interrogated simultaneously. The sensitivity and low noise demonstrated by the detection system is expected to allow the use of cheap, stable, LED light sources in practical systems.

A micromachined sensor array has been developed for the rapid characterization of multi-component mixtures in aqueous media. The sensor functions in a manner analogous to that of the mammalian tongue, using an array composed of individually immobilized polystyrene-polyethylene glycol composite microspheres selectively arranged in micromachined etch cavities localized o n silicon wafers. Sensing occurs via colorimetric or fluorometric changes to indicator molecules that are covalently bound to amine termination sites on the polymeric microspheres. The hybrid micromachined structure has been interfaced directly to a charged-coupled-device that is used for the simultaneous acquisition of the optical data from the individually addressable `taste bud' elements. With the miniature sensor array, acquisition of data streams composed of red, green, and blue color patterns distinctive for the analytes in the solution are rapidly acquired. The unique combination of carefully chosen reporter molecules with water permeable microspheres allows for the simultaneous detection and quantification of a variety of analytes. The fabrication of the sensor structures and the initial colorimetric and fluorescent responses for pH, Ca⁺², Ce⁺³, and sugar are reported. Interface to microfluidic components should also be possible, producing a complete sampling/sensing system.

A regenerable channel waveguide fluorescence sensor for environmental monitoring is reported. The sensor has been characterized as a detector of the pesticide 2,4 dichlorophenoxyacetic acid. A binding inhibition assay, using fluorescent Cy5.5 dye-labeled antibodies, was monitored at the modified surface of the glass waveguide to detect the target analyte. Three calibration curves were determined and averaged. The averaged calibration curve has a mid-point of 0.68 ppb and a calculated detection limit of 0.28 ppb. Incorporation of a 20 nm thick tantalum pentoxide film at the waveguide surface enhanced the peak fluorescence signal by a factor of approximately 6 compared with an uncoated sensor.

Semiconductor processing tools that use a plasma to etch polysilicon or oxides produce residue polymers that build up on the exposed surfaces of the processing chamber. These residues are generally stressed and with time can cause flaking onto wafers resulting in yield loss. Currently, residue buildup is not monitored, and chambers are cleaned at regular intervals resulting in excess downtime for the tool. In addition, knowledge of the residue buildup rate and index of refraction is useful in determining the state of health of the chamber process. We have developed a novel optical fiber-based robust sensor that allows measurement of the residue polymer buildup while not affecting the plasma process.

A miniaturized microanalytical device for the simultaneous monitoring of different metabolites was realized by assembling of a biosensor array produced by thin film technology with a flow-through cell produced by printed circuit board technology. The biosensor array comprises four working electrodes which can be individually configured. Glucose and lactate devices were made for whole blood monitoring. Ex vivo experiments, performed on animals, where the device was continuously operated in an extracorporeal undiluted heparinized blood stream without loss in sensitivity for 48 hours, gave close tracing to routinely used clinical analyzers by using one point in vitro calibration.

In the development of chemical analysis systems a clear trend exists towards miniaturization using silicon micromachining. This paper reports on microflow devices such as microvalves, micropumps and bioreactors developed for the application to analytical chemistry. As examples, the design and performance of integrated enzyme-based analysis systems for the determination of gas-phase ethanol will be described.

Quartz crystal resonators (QCR) coated with various selected sensitive polymers have been investigated for the detection of organic compounds in liquid phase. The targeted organic compounds are tetrachloroethane, trichloroethylene, tetrachloroethane, chloroform, toluene, and xylenes in aqueous solutions. Under optimized experimental conditions using properly designed measurement flow cells and oscillator circuits, proper flow rate, and different coating thicknesses, low detection limits for organic compounds have been achieved. Detection limits as low as 150 ppb and 500 ppb have been achieved with short response time, reversibility and reproducibility using PEA-coated QCR operating at the series-resonant frequency, f_s, for tetrachloroethane and trichloroethylene, respectively. Such limits together with the response time clearly indicate that the coated sensors can be used for real-time water analysis. Moreover, using the measured frequency changes, the partition coefficients, K_L, of the analyte molecules in the coating/water composite are discussed in order to analyze the sensor mechanism and implement sensor and sensor arrays. Preliminary results on the detection of binary mixtures of analytes are presented and discussed.

A series of soluble dodecylsulfanyl phthalocyanines for the detection of organic vapors are investigated utilizing interdigital transducer electrode structures on a glass substrate and quartz crystal resonators. The sensing properties are studied by measuring changes in the transducer/coating composite properties upon exposure to the organic solvent vapor. The sensor parameters of interest are the electrostatic capacitance and the resistance of the composite collected by impedance methods, and the series- and parallel-resonant frequencies (f_s and f_p) of coated quartz-based oscillators. The results show that these multiple sensor parameters can be used to implement a multi- information sensor system. In addition, the interaction mechanism between the volatile organic molecules and the investigated phthalocyanine coatings are discussed utilizing the partition coefficients of the vapor molecules, and possible changes in electrical properties in the coatings.

Liquid flow cells have been fabricated to prepare an array of QCMs operating simultaneously for detection and identification of VOCs in water. Two signals, a frequency response and a damping voltage response, were obtained per resonator. A blank QCM was used as a reference to account for changes in liquid density and viscosity. Nine different polymer coatings applied using a spin coat technique have been examined for VOC response under liquid flow conditions. A matrix of three classes of VOCs were examined for each coating with four chemicals in each class. The three classes of VOCs are polar, nonpolar and chlorinated. A pattern recognition technique, called visually empirical region of influence, was used to cluster the responses in n- dimensional space. Chemicals within a class varying by only one methyl group (e.g., toluene and xylene) are easily discriminated using only two different coatings with three different QCM responses. All chemicals were easily separated and detected with a total of 5 films and 6 responses with >99% accuracy.

The work functions principle of gas sensing is dedicated for room or slightly elevated temperature of operation as signal contributions from physisorption as well chemisorption will be detectable. The sensor principle best suited for these conditions are FET transistors either with diffusible gates made of Palladium or polymers or designed with an air gap that makes the inner surface of the gate capacitance accessible to gases. The latter allow to incorporate almost all groups of sensitive materials if a hybrid construction is used. In comparison to the broad investigations made on conductivity sensors the development of sensing layers specific for work function gas-FET is in an early state. However, the models available for metal oxides or electrochemistry can be adopted to this surface potential method. The sensors allow to use the electroadsorptive effect and withstand a field test, e.g. for ozone detection. As the results show, work function sensors are capable for obtaining micro gas sensors with low power consumption suitable for low cost applications.

A new generation of solid state sensors based on nanocrystalline BaTiO₃ films containing various semiconducting oxides has been developed. The sensors were fabricated from BaTiO₃ based nanopowder mixtures using thick film technology and were characterized regarding their CO₂-gas sensitivity at different operation temperatures and gas environments. It was found that the sensors operate over a wide range of CO₂ concentrations. Interfering gases have only minor effects on the sensor response. By using miniaturized Al₂O₃-substrates as carriers for the sensitive nanocrystalline layer a significant decrease of the power and powder consumption for each sensor was achieved.

The bottleneck in the development of chemical sensors is the design of the coatings for chemical recognition of the analyte. One pronounced method is to tailor supramolecular cavities for different analytes. Polyfunctional linkers or the embedding of these materials in a polymeric matrix can improve stability and response time of the sensor. An even more favorable method to synthesize chemically sensitive layers is realized by molecular imprinting, since a rigid polymer can be generated directly on the transducer of interest and may be included in its production process. The analyte of interest acts as a template during the polymerization process and is evaporated or extracted by suitable solvents. Due to the cavities formed this polymer enriches analyte molecules, which can be detected by mass- sensitive devices such as QMB or SAW resonators or by optical measurements. This procedure allows both the detection of polycyclic aromatic hydrocarbons (PAHs) with fluorescence or mass sensitive devices. If the print PAHs are varied the polymers are tuned to the desired analyte. The enrichment of solvent vapors or other uncolored specimen by the layer can also be followed by the embedding of carbenium ions used as optical labels.

In the current paper a dual-delay-line- and a resonator- device based on CMOS-silicon-technology is presented. As a piezoelectric layer ZnO is used. The layer was deposited at room temperature in a RF magnetron sputter process. Using x- ray diffraction it could be shown that the crystals are mostly oriented with the c-axis (hexagonal structure) perpendicular to the surface which is necessary to conduct surface acoustic waves. Pt electrodes were designed for frequencies between 140 and 600 MHz and were deposited on top using a lift-off-process. A poly-silicon heating resistor was integrated as a sublayer for controlling and changing of the temperature of the SAW-device for studying the influence of temperature on the mass sensitive layer. A Pt thin film resistance served for temperature measurement. The performance of the devices were compared to standard quartz based SAWs.

Multi gas sensor systems are often the only way for increasing selectivity of a gas measurement in a given environment. It is shown that the cycled heating of sensor membranes give the possibility for quantitative analysis of gas mixtures. In addition the integration of several thermally decoupled sensor elements with different gas sensitivities on one silicon chip is possible. On the other hand for hand held devices low power consumption is necessary. In this paper we present results on a microstructured silicon substrate with different gas sensors, each placed on a thermally insulated silicon membrane, optimized for cycled heating.

Amorphous Diamond like carbon (DLC) thin films were deposited on to 4'-silicon wafers by an electron cyclotron resonance microwave excited methan (CH₄) or ethin (C₂H₂) plasma at low pressure. Electronic characterization of DLC films were performed by I/V and C/V measurements using MIS-structures. Whereas the electrochemical pH-characteristics were measured using ion- sensitive field-effect transistors. It is shown, that the type of carrier transport mechanism in DLC films depends on the process conditions and that the electrical conductivity varies over a wide range. This can be adjusted mainly by the kinetic energy of the C_xH_x⁺ ions and the C to H ratio, which depends on the type of process gas. The dominant charge transport mechanism in DLC films based on a methan plasma is the Poole-Frenkel emission whereas the charge flow for ethin based DLC films is space-charged limited. The electronic conductivity of DLC films deposited with ethin as process gas is typically about five orders of magnitude higher than methan based films. The electrochemical characterization shows a pH-sensitivity in the range of 50 - 57 mV/pH and a long-term pH signal stability in the range of 0.3 - 25 (mu) V/h. Based on the different pH-sensitivities int will be possible to produce a pH-sensor in differential mode using DLC/DLC or DLC/Ta₂O₅ combinations for the sensitive layers.

A self-contained, hand-held, optical waveguide, chemical detection system has been built to detect and quantify gases and vapors. The system uses a hybrid integrated circuit (IC) containing optical waveguides coated with sensing chemistry as the optical platform. The IC with sensing chemistry is available commercially under the name Sensor-on-a-Chip. This IC is mounted in a small, uniquely designed sample chamber where the measured analyte is identified by the sensing chemistry and biochemistry. Continuous or stop-flow sampling is possible. Sensitivities in the low parts-per-million have been attained for hydrocarbons and alcohol. Analyte coverage is only limited by the sensing chemistries and biochemistries that are available.

In order to meet the stringent demands of natural and waste waters monitoring for artifact-free data, an increasing effort is directed towards developing on-line and in-situ measuring schemes. In this context, the development of microfabricated electrochemical detectors for stripping analysis of trace metals has attracted particular attention. In this paper we report on the fabrication and analytical performance of a microfabricated electrode for direct Square Wave Anodic Stripping Voltammetry analyses of trace metals in natural waters. It is based on a mercury-plated thin-film Ir microdisk array covered by a layer of an antifouling gel. To facilitate the control of the gel deposition and to improve its mechanical stability, a polymeric containment ring has been formed around the array. The sensor is then integrated within a complete Voltammetric In situ Profiling analytical system.

Mercury and other toxic, heavy metals must be detected at part per billion levels in drinking water and environmental monitoring applications. No portable technology is presently capable of providing the required sensitivity, simplicity or reliability. Piezoelectric sensor technology and electrochemical technology have both offered sound approaches to the detection of these pollutants. Both exhibit limitations which prevent their widespread acceptance in water quality assurance and in environmental remediation.

In order to study the influence of several atmospheric parameters on Figaro type gas sensors response, we have designed a test equipment which allows us to characterize these kind of sensors under conditions of closely controlled temperature, humidity and contaminant gas concentrations. This equipment is mainly composed of a gas humidification system to satisfy the humidity and temperature control conditions, and a test chamber which enclose the sensors to be characterized. At first, this paper presents the developed system and its main requirements. Then, preliminary results are presented, showing the influence of the relative humidity on the behavior of an array of these sensors.

In this paper, we present the characterization of three different Figaro gas sensors, TGS 832, TGS 813 and TGS 800. These sensors were exposed to forane R134a, carbon dioxide and mixtures of these gases in synthetic air. They present different behaviors in term of steady-state value and dynamic response. This will lead to many informations which may be studied by to a pattern recognition method to discriminate between the different gases. We also have pointed out some drawbacks due to the contaminant and drift effects.

The investigation of specific interactions in biological media requires the development of sensors, combining principles of biochemical recognition and a suitable transduction. In this work a quartz crystal microbalance system was coated with highly ordered lipid films. It was shown that this application can be taken as a model system to study the adsorption behavior of supramolecular structures. To simulate biomimetic structures, we used a combination of `Self Assembling' and `Langmuir-Blodgett' techniques. Glycolipids were incorporated into LB-films as target structures to mimic a native glycocalix.

In this report we presented results of gas sensitivity' kinetics analysis for undoped SnO₂ thin films, deposited by spray pyrolysis method, using SnCl₄x5H₂O alcohol solution. The comparison of gas sensitivity's kinetics in measurement cycles air yields {air+(0.08 - 1.7%)CO} yields air and air yields (N₂ + 0.5%O₂} yields air for different thickness of SnO₂ films (d equals 40 - 200 nm) and operating temperature (T equals 150 - 400 degree(s)C) was carried out. We have determined the kinetic parameters ((tau) and E_act) and made a conclusion that kinetics of gas sensitivity is limited by the rate of SnO₂ surface refilling by oxygen.