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Mono-dispersed polystyrene-based microspheres with diameters about 1 μm encapsulating rhodamine moieties as oxygen insensitive internal reference probes and platinum octaethylporphyrin units as oxygen sensitive probes were synthesized as new ratiometric oxygen sensors (Rhod-PtOEP-PS). The dual luminophors of rhodamines and platinum porphyrin moieties exhibited emissions maxima at 585 nm and 644 nm, respectively. The microspheres showed good oxygen sensing properties in different oxygen partial pressures (pO2) and dissolved oxygen (DO) concentrations. It was found the oxygen probes and reference probes in microspheres showed higher photo-stability than their corresponding free fluorophores in solution. The microspheres also showed good sensitivity for air-pressure and cellular oxygen in cell culture medium. These microspheres were used to detect DOs in a few kinds of liquids including some daily drinks and it was found the measured errors were within positive/negative 11% as compared with the measured results using traditional oxygen electrodes.

Incorporation of palladium nanoparticles on the surface of multi-walled carbon nanotubes and modification of glassy carbon electrode with the prepared nano-hybrid material led to the fabrication of a novel electrode. The modified electrode showed attractive electrocatalytic activity and sensitizing effect on luminol-O(2) and luminol-H(2)O(2) electrochemiluminescence (ECL) reactions at neutral media. The sensitized luminol-O(2) and luminol-H(2)O(2) reactions were successfully applied for the ECL determination of dissolved O(2) and glucose, respectively. Under the optimal conditions for luminol-O(2) system, the ECL signal intensity of luminol was linear with the concentration of dissolved oxygen in the range between 0.08 and 0.94 mM (r=0.9996) and for luminol-H(2)O(2) system, the ECL signal intensity of luminol was linear with the concentration of glucose in the range between 0.1 and 1000 μM (r=0.9998). The limits of detection (S/N=3) for dissolved oxygen and glucose were 0.02 mM and 54 nM, respectively. The relative standard deviations (RSD) for repetitive measurements of 0.50 mM oxygen (n=10) and 10 μM glucose (n=30) were 3.5% and 0.3%, respectively. Also, under the optimal conditions for luminol-H(2)O(2) system, the ECL signal intensity of luminol was linear with the concentration of H(2)O(2) in the range between 1 nM and 0.45 mM (r=0.9997). The limit of detection (S/N=3) for H(2)O(2) detection was 0.5 nM and the relative standard deviation for repetitive measurements of 10 μM H(2)O(2) (n=10) was 0.8%.

A scheme for the simultaneous determination of oxygen and temperature using quantum dots and a ruthenium complex is demonstrated. The luminescent complex [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)]2+ is immobilized in a non-hydrolytic sol-gel matrix and used as the oxygen sensor. The temperature information is provided by the luminescent emission of core-shell CdSe-ZnS semiconductor nanocrystals immobilized in the same material. Measurements of oxygen and temperature could be performed with associated errors of +/-2% of oxygen concentration and +/-1 degrees C, respectively. In addition, it is shown that while the dye luminescence intensity is quenched both by oxygen and temperature, the nanocrystals luminescent emission responds only to temperature. Results presented demonstrate that the combined luminescence response allows the simultaneous assessment of both parameters using a single optical fiber system. In particular, it was shown that a 10% error in the measured oxygen concentration, induced by a change in the sample temperature, could be compensated using the nanocrystals temperature information and a correction function.

An optical bio-sniffer for methyl mercaptan (MM) one of major odorous chemicals in halitosis (bad breath) was constructed by immobilizing monoamine oxidase type A (MAO-A) onto a tip of a fiber optic oxygen sensor (od: 1.59 mm) with an oxygen sensitive ruthenium organic complex (excitation: 470 nm, fluorescent: 600 nm). A flow cell for circulating buffer solution was applied to rinse and clean the tip of the device like nasal mucosa. In order to amplify the bio-sniffer output, a substrate regeneration cycle caused by coupling MAO-A with l -ascorbic acid (AsA) as reducing reaction with reagent system was applied to the sensor system. After evaluating the sensor characteristics using a gas flow measurement system with a gas generator, the optical bio-sniffer was applied to expired gases from healthy male volunteers for halitosis analysis as a physiological application. The optical bio-sniffer was applied to detect the oxygen consumption induced by MAO-A enzymatic reaction (and AsA chemical reduction) with gaseous MM application. The bio-sniffer was calibrated against MM vapor from 8.7 to 11500 ppb with correlation coefficient of 0.977, including a MM threshold (200 ppb) of pathologic halitosis and the human sense of smell level 3.5 (10.0 ppb), with good gas-selectivity based on the MAO-A substrate specificity. As the result of the physiological application, the optical bio-sniffer could successfully monitor the MM level change in breath samples during daytime, which is consistent with the previously reported results.

A study of migration of the active components of oxygen sensors into food is presented. Six types of sensors, based on different oxygen sensitive dyes (two metalloporphyrins and one ruthenium dye), polymers (polystyrene and polysulfone) and support materials, were exposed to a number of standard ‘food simulants’ recommended by FDA/EU guidelines and then assayed for migration or sensor components and changes in oxygen calibration. Both metalloporphyrin sensor dyes leached only in olive oil and in 95% ethanol (used as a positive control), at maximum levels of 19.22 μg/dm 2 for PtOEPK and 113.96 μg/dm 2 for PtTFPP. The RuDPP dye showed maximum leaching in 95% ethanol (25.19 μg/dm 2 ) while also migrating in an acidic aqueous simulant. Planar supports such as polyester tended to enhance the stability of the sensor. Migration of the styrene monomer from the polystyrene encapsulation medium was concluded to be low enough to be insignificant. Migration of sensor components was shown to correlate with the changes in sensor response to oxygen. Based on these results, sensor combinations were ranked on the basis of their resistance to leaching and their general stability, safety and suitability for use on a large scale in packaged foods and related food applications was proven.

Accurately measuring dissolved oxygen concentrations in fresh and salt water environments has long been an interdisciplinary priority. Many methodologies exist, including two very promising new ones, optical fluorescence quenching optrodes (or optodes) and solid-state voltammetric electrodes. In this study we compare the responsiveness of these two techniques to dynamic changes in dissolved oxygen concentrations, using traditional methods of polarographic oxygen sensors and Winkler’s chemical titrations to corroborate the measurements. Advantages of the optrode system include simplicity of operation and high sensitivity when changes in oxygen concentrations are small (

An optical oxygen-sensing material based on the fluorescence intensity changes of pyrene-1-butyric acid (PBA) chemisorption film has been developed and characterised. The fluorescence intensity of PBA film decreased with increase of oxygen concentration. The I 0 / I 100 value of PBA film is estimated to be 6.14±0.15 and large Stern–Volmer constant ( K SV =0.028±0.13 Torr −1 ) is obtained. After irradiation for 24 h with 150 W tungsten lamp, little changes of oxygen-sensing properties were observed. These results indicate that PBA film is highly oxygen-sensitive and photostability device. The response times of the PBA chemisorption film were 10.0 s for switching from argon to oxygen, and 53.0 s for switching from oxygen to argon. Moreover, the optical sensor based on the PBA chemisorption film was applied to the measurement of oxygen concentration in aqueous solution.

An optical oxygen sensor based on the luminescence intensity changes of tris(2-phenylpyridine anion) iridium(III) complex ([Ir(ppy) 3 ]) immobilized in fluoropolymer, poly(styrene- co -2,2,2-trifluoroethyl methacrylate) (poly(styrene- co -TFEM)) film was developed. The luminescence intensity of [Ir(ppy) 3 ] in poly(styrene- co -TFEM) film decreased with increase of oxygen concentration. The ratio I 0 / I 100 (a sensitivity of the film, where I 0 and I 100 represent the detected luminescence intensities from a film exposed to 100% argon and 100% oxygen, respectively) value of [Ir(ppy) 3 ] in poly(styrene- co -TFEM) film is estimated to be 15.3. A Stern–Volmer plot of the [Ir(ppy) 3 ] film exhibited considerable linearity ( r 2 =0.998) and the Stern–Volmer constant, K SV is estimated to be 0.02 Torr −1 , indicating that a highly sensitive oxygen sensor is developed using [Ir(ppy) 3 ] immobilized in poly(styrene- co -TFEM) film.

The silicon based semiconductor structure Si/SiO2/Si3N4/LaF3/Pt can be used as a potentiometric oxygen sensor working at room temperature. A thermal re-activation can be applied to overcome the earlier disadvantage of an increase in response time with continuous use. Using the Pt gate electrode as a resistive heater, very short electrical high-power pulses can be applied. A heating time as short as 300 ns was sufficient for the re-activation of the sensor. This way, only the sensitive thin layer system LaF3/Pt was heated, and the whole sensor was at room temperature immediately after heating. Impedance spectroscopy, X-ray photoelectron spectroscopy (XPS) and quadruple mass spectrometric (QMS)–thermogravimetry (TG) were used to investigate the mechanism of deterioration in dynamic sensor behaviour and re-activation. The formation of hydrated carbonate and the desorption of CO2 and H2O have been shown to be the causes. © 2001 Elsevier Science B.V. All rights reserved.

The feasibility of enhancing the preconditioning time property of the planar type amperometric oxygen sensor is investigated. A gas permeable membrane is formulated by incorporating hydrophilic polyurethane (HPU) into a one-component room temperature vulcanizing (RTV) silicone rubber matrix. Planar oxygen sensors are made by forming a recipient hydrogel layer on the base electrodes screen printed on a substrate, and by covering the hydrogel layer with a gas permeable membrane. The optimized RTV/HPU (70/30 wt.%) yields a gas permeable membrane with fast water vapor transport that allows for fast hydration of the inner hydrogel layer, yet is not permeable to chloride ions that could interfere with oxygen measurements by changing the potential of the inner Ag/AgCl reference electrode. The proposed RTV/HPU-based planar oxygen sensor is shown to exhibit enhanced preconditioning time property (i.e. time required to reach 95% of the steady-state current=2 s) with a sensitivity (slope: 1.1 nA/mmHg) and a linearity (correlation coefficient: 0.999 in the range of 0.6–268 mmHg) that are adequate for dissolved oxygen measurements in physiological samples.

The design and analytical characterization of a fiber-optic instrument for simultaneous multiposition water-dissolved oxygen monitoring by room-temperature phosphorescence (RTP) measurements is presented. The sensing principle is based on the RTP quenching by oxygen of the phosphorescent light emitted by the metal chelate formed by Al with 8-hydroxy-7-iodo-5-quinolinesulfonic acid (Al-ferron) trapped in a sol–gel solid support. Four RTP oxygen sensor flow-cells are assembled in order to measure the oxygen content in four different water streams. A xenon flash-lamp is used as the single excitation source for the four sensing regions, while multichannel phosphorescence detection is achieved by using a cooled intensified charge-coupled device (ICCD). Four bifurcated optical fibers are used to carry the light from the excitation source to the sensing active surface in the flow-cell and to bring the emitted RTP to the detector. The RTP light coming from each of the optical fibers was focused onto different sites (rows of pixels) of the ICCD. In this way, the RTP signals from each of the four sensing materials packed in the flow-cells can be differentiated and measured. Simultaneous dissolved oxygen monitoring in several water streams containing different dissolved oxygen levels is demonstrated by using the proposed instrumentation. Also, the relatively long phosphorescence lifetime of the materials used allow the use of the developed instrumentation to perform lifetime room-temperature phosphorescence measurements.

To overcome the quenching effect of oxygen in fluorescence spectrometry, an in-line flow degassing device (FDD) was successfully applied to the removal of oxygen from sample solutions. The FDD consisted of a 3 m long coil of capillary silicone rubber tubing, installed in a glass flask maintained under reduced pressure of N2 (2.400 Pa). To avoid recontamination of the emerging flow with O2, the connection of the silicone tube with the fluorimetric cell is made with flexible silica capillary tube. Solutions can be injected with a syringe or feed with a pump. Aqueous solution of ruthenium(II) tris-bipyridil chloride, subject to quenching by oxygen, served as a luminescent probe. The performance was checked against independent amperometric measurements of O2 with a Clark cell, that correlated well with the O2 obtained from the fluorescence data using the Stern–Volmer relationship. At a flow rate of 1.0 ml min−1, the concentration of O2 (measured amperometrically) dropped from 8.24 mg l−1 to 15 μg l−1 for a residence time of 34 s in the FDD, rendering the oxygen quenching effect on [Ru(bipy)3]2+ undetectable. The FDD compares favorably with direct inert gas purging of the solution in efficiency and speed. Moreover, it is compatible with flow injection analysis. A frequency of 35 determinations per hour was attained at 1 ml min−1, with good repeatability of the peaks (R.S.D.=0.8%, n=25 injections of 200 μl of 1×10−4 M [Ru(bipy)3]2+).

A series of fluoropolymers, poly(isobutylmethacrylate-co-trifluoroethylmethacrylate) (poly-IBM n -co-TFEM m ) with different ratios of IBM and TFEM units, were synthesized and applied as an optical oxygen sensing matrix using luminescence quenching of metalloporphyrins, platinum and palladium octaethylporphyrin (PtOEP and PdOEP), by oxygen. For PtOEP in poly-IBM n -co-TFEM m films, Stern–Volmer plots exhibit considerable linearity at oxygen concentrations between 0 and 100%. For PdOEP in poly-IBM n -co-TFEM m films, however, the Stern–Volmer plots exhibit considerable linearity at lower oxygen concentrations between 0 and 20.0%. These results indicate that PtOEP and PdOEP films are useful optical oxygen sensors for oxygen concentration range between 0 and 100% and between 0 and 20.0%, respectively. The K SV values increased with increasing of TFEM unit in poly-IBM n -co-TFEM m . The response times of PtOEP and PdOEP immobilized in poly-IBM 1 -co-TFEM 3.28 films were 5.7 and 3.0 s on switching from argon to oxygen and 80.0 and 197 s on switching from oxygen to argon, respectively. This result indicates that PtOEP and PdOEP immobilized in poly-IBM n -co-TFEM m films represent a highly sensitive device for oxygen.

Experimental results from a phosphorescence-based fiber-optical oxygen sensor are presented. The optical oxygen sensor module has overall dimensions of 6 × 6 × 12 mm3. Erythrosin B immobilized in sol–gel silica, which showed strong phosphorescence quenching by oxygen, was used in the sensor probe. Oxygen sensing is effective from 0.014 to 600 mbar. On account of the long phosphorescence lifetime (∼0.28 ms) and high phosphorescence yield (∼2%) of erythrosin B in sol–gel silica at room temperature, the sensitivity of the sensor improves by a factor of 10 as compared to transition-metal complex-based optical fiber oxygen sensors. The phosphorescence quenching effect is highly selective to oxygen. The sensor is inert to commonly found gases such as nitrogen and argon. Time-decay of phosphorescence is also studied.

An aluminum 2,9,16,23-tetraphenoxy-29H, 31H-phthalocyanine hydroxide (AlPc(OH))–polystyrene (PS) film was prepared and its photophysical and photochemical properties were measured. An optical oxygen sensor based on the fluorescence quenching of AlPc(OH)–PS film by oxygen was developed. The ratio I0/I100 is used to describe the sensitivity of the sensing film, where I0 and I100 represent the detected fluorescence intensities from a film exposed to 100% argon and 100% oxygen, respectively. The I0/I100 of AlPc(OH)–PS film is estimated to be 1.04. A Stern–Volmer plot of the film exhibited considerable linearity in low oxygen concentration region (∼10%) and the Stern–Volmer constant, KSV is estimated to be 2.4 × 10−3%−1.

An optical oxygen (O2) sensor consisting tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ditetrakis(4-chlorophenyl)borate adsorbed on silica gel has been successfully fabricated and used to continuously monitor O2 gas at low concentration. The luminescence material shows a very strong and stable pink emission when excited by blue light and it is efficiently quenched by O2. The calibration of the optical sensor can be simply done by a single standard flow injection method. The results demonstrate excellent linear Stern–Volmer behaviour when O2 concentration is at low levels (0.0–0.05% v/v), but the Stern–Volmer plot has a slightly downward curvature at higher O2 levels. The two-site quenching model correlates well with the calibrated O2 concentration range (0.0–0.55%). The t95 response times of the sensor are

Two types of all-solid amperometric sensors, incorporating Nafion ® as the solid ionic conductor and exhibiting microelectrode behaviour, have been used as gaseous oxygen probes in the 1–25% (v/v) concentration range. The first one involved a Pt or Ag microdisc surrounded by a ring of the anode material, the two electrodes being in the same plane and covered by a solution-recast Nafion ® film. In a modified version of this type of sensor, a Au microband was used as the indicator electrode. Well-defined sigmoidal voltammograms for oxygen reduction from the gas phase were obtained and, when used in a constant potential mode, the sensing device showed good linearity ( r 2 =0.9998–0.9988) with oxygen concentration in the gas stream and a satisfactory sensitivity of 8×10 −5 A cm −2 (%v/v) −1 . The high detection limit of 2% (v/v), however, restricts the possible applications to crude monitoring in the higher oxygen concentration range. In the second type of sensor, Au electrodes were vacuum-deposited as thin layers on the same face of a Nafion ® membrane and a strip of uncovered ionic polymer between the two metal layers ensured completion of the electrical circuit. The gas samples were in contact with the electrode layers and oxygen reduction led to an exponential current rise over a wide potential range indicating very high mass transport rates. The sensitivity of the device was 20 nA (%v/v) −1 and it is suggested that with such a sensor configuration the electroactive gas reacts at the line formed by the gas/solid electrolyte/metal layer interface, i.e. at a virtual microband electrode.

A new fiber-optic sensor for oxygen has been developed. Tetraphenylporphyrin (TPP), embedded into the original analyte- permeable cladding of a conventional low cost plastic-clad silica optical fiber, is excited by the evanescent-wave traveling in the fiber; the resulting fluorescence is captured back into the guided modes of the fiber and can be detected at either end. Oxygen in the surrounding medium quenches the fluorescence and is quantified by means of the Stern–Volmer expression. Excitation was achieved with an ultra-bright (13 000 mcd) yellow 590 nm light-emitting diode (LED), with emission monitored at 650 nm. The new sensor offers excellent precision (relative standard deviation (RSD) of 0.1–0.2%) over the range of measured oxygen partial pressures (55–760 torr), a response time of 1 s, a detection limit of 3.5 torr of oxygen, and a quenching constant of 7.5×10−4 torr−1. Unlike earlier oxygen sensors, the new device is immune to changes in relative-humidity of measured gaseous samples. The short (10 ns) fluorescence lifetime of TPP and the possibility to fabricate continuous chemically sensitive fibers hundreds of meters long make the sensor attractive in applications that require spatially resolved oxygen mapping over large remote areas.

A mathematical model is derived from the Stern–Volmer equation as a practical calibration function for various optical oxygen sensors based on quenching of ruthenium fluorescence. The model is simple and flexible, and is ideal for computing oxygen partial pressure from 0 to 760 Torr in gaseous samples, and 0 to 200 Torr in aqueous samples. Feasibility of this model for dissolved oxygen calibration is demonstrated by applying the model to data acquired from a set of three radioluminescence-based optical oxygen sensors. The model is applicable to various sensor designs and adequately accounts for stray radiation and other sources of non-quenchable light.

Leaking of immobilized fluorescent indicators from the sensing matrix affect the stability of optochemical sensors and, therefore, presents a major problem in this field. When a polymer is used as a matrix support, a covalent bonding of the fluorescence indicator to the matrix eliminates the leaking problem. However, covalent bonding of the indicator to the support cannot be used as a general approach since it may modify the spectral properties of the indicator and its sensing response toward the analyte. This paper describes the synthesis of a modified ruthenium phenanthroline complex which is suitable for acryl co-polymerization with acrylamide. The newly synthesized dye, tris (5 acrylamido, 1,10 phenanthroline) ruthenium chloride, Ru(5-acrylamido-phen)3, maintains its full oxygen response with a slight decrease in its quantum yield for emission. Leaking measurements show a significant improvement in the stability of fiber-optic oxygen sensors that use Ru(5-acrylamido-phen)3 as an oxygen sensitive fluorescence indicator, over previous fiber-optic oxygen sensors that make use of other ruthenium diimine complexes for oxygen measurement. The improvement in stability is particularly noticeable in samples of increased hydrophobicity.

The response of a Clark type oxygen sensor, designed for the study of benthic fluxes in the marine environment, was evaluated with respect to variations in oxygen concentration, temperature, pH, salinity, total pressure, fugacity ([O2]water/[O2]satwater) and stirring rate by means of an experimental design evaluated by partial least squares (PLS). Fugacity and temperature not only explained a major part of the response, but also stirring-rate and the cross term temperature∗fugacity were significant on the 95% level. With the obtained results, a model for predicting absolute oxygen concentrations from the sensor response was created. To verify the practical applicability of the model it was used to predict oxygen concentrations from sensor data obtained in situ during a cruise in the Skagerrak (north-eastern North Sea). Predicted concentrations were then compared, and found to be in accordance (within 5 %) with concentrations obtained from Winkler titrations. The results suggest that fugacity and temperature are the most important factors to consider while using this, and probably other, brands of Clark type oxygen macro sensors.

Inorganic silica glass loaded with platinum octaethylporphyrin (PtOEP), an oxygen-quenchable luminescent dye, was prepared by acidic hydrolysis and condensation of tetraethyl orthosilicate (TEOS), and the optical properties such as absorption and luminescence spectra were investigated. Using these materials, an optical oxygen sensor was fabricated, based on the phosphorescence quenching of PtOEP, which responded in the range of 0.5–100% O2. For this sensor operational stability and photostability were enhanced compared to a polymer matrix-based sensor

A novel and simple potentiometric oxygen sensor suitable for the measurement of partial pressure of oxygen (Po2) in flowing blood is described. The sensor is based on measuring a steady-state mixed potential that originates at the surface of a cobalt wire electrode. This mixed or corrosion potential arises from the slow oxidation of cobalt and simultaneous reduction of oxygen at the electrode surface, and changes as a function of sample Po2 levels. The probe is fabricated with an outer gas permeable silicone rubber tubing (1.06 mm o.d.), which contains an internal buffer solution (25.0 mM potassium hydrogen phthalate, pH 4.0, containing 1.0 mM KCl), a cobalt wire (0.1 mm o.d.) as the working electrode and an Ag/AgCl wire as the reference electrode. The sensor characteristics (slope, detection limits, linear range, drift rates, etc.) along with the response mechanism based on mixed potential are discussed in detail. In vitro evaluation of catheter forms of the sensors performed in a blood loop indicate that the proposed sensor design can closely follow Po2 changes induced in blood during 2–3 h of continuous monitoring.

The sensitivity of a membrane-covered oxygen gas sensor under the influence of gas flow has been tested experimentally. As the oxygen sensor is placed in different positions relative to the air-pump and gas flow meter, the effect of gas flow-rate on the response of the sensor is notable. By choosing appropriate connective modes, the Clark-type sensor may be made insensitive to the gas flow-rate. This sensitivity to flow results from the change in gas pressure in the sensor gas chamber. The relationship between the sensor response and the gas flow-rate is discussed.

The oxygen effect on a glucose oxidase based implantable glucose sensor was investigated based on studies of tissue oxygen availability and demand for oxygen by the glucose sensor. In vitro measurements showed that the oxygen effect is directly related to the glucose sensor sensitivity and linearity. Results of in vivo measurements in rat subcutaneous tissue with simultaneously implanted oxygen sensor and glucose sensor also suggested similar influence. A practically useful glucose sensor that is essentially free of oxygen fluctuation can be constructed by controlling its sensitivity and linearity.

The optimum performance of an optical oxygen sensor based on polysulfone (PSF)/[Ru(II)-Tris(4,7-diphenyl-1,10-phenanthroline)] octylsulfonate (Ru(dpp)OS) was checked by carefully tuning the parameters affecting the membrane preparation. In particular, membranes having thickness ranging between 0.2 and 8.0 μm with various luminophore concentrations were prepared by dip-coating and tested. The membrane thickness was controlled by tuning the solution viscosity, and was measured both by secondary ion mass spectrometry (SIMS) and by visible spectroscopy (Vis). Luminescence-quenching-based calibration was a single value of the Stern–Volmer constant ( K ′ SV ) for membranes containing up to 20 mmol Ru(dpp) g−1 PSF (1.35 μm average thickness). The K ′ SV value decreased for larger concentration. The highest sensitivity was obtained with membrane thickness around 1.6 μm, having a response time close to 1 s. Thicker membranes exhibited an emission saturation effect and were characterized by longer response time. The K ′ SV behavior was interpreted on the basis of a mathematical approach accounting for the contribution of luminescence lifetime (τ0), oxygen diffusion coefficient ( D O 2 ) and oxygen solubility inside the membrane ( s O 2 ) establishing the role of all of them and allowing their experimental determination. Moreover, a simple experimental way to estimate K ′ SV without needing calibration was proposed. It was based either on the light emission asymmetry or on the percent variation of light emission on passing from pure nitrogen to pure oxygen.

A measurement system, consisting of an optochemical glass capillary oxygen sensor, an optoelectronic measuring unit and a microdialysis catheter (CMA 60) for the extraction of the biological fluid from the subcutaneous adipose tissue of critically ill patients is reported. The capillary sensor is based on the oxygen sensitive dye platinum (II) meso-tetra(pentafluorophenyl) porphyrin (Pt-TFPP) incorporated in a polystyrene matrix. The measuring system has been tested in vitro and in vivo. In particular in vitro long-term stability of the sensor has been investigated in different measurement media (elomel, 5% mannitol, Ringer, dialysed blood). The influence of different flow rates from 0.1 up to 7.0 microl min(-1) on the sensor response as well as the oxygen recovery rate are discussed. The presented measurement system allows the measurement of oxygen in biological fluid in the range from 0 to 300 mmHg, with a resolution better than 1 mmHg and high accuracy (better than +/-1 mmHg absolute). Finally, the suitability of the described measurement system for the continuous oxygen monitoring in subcutaneous adipose tissue has been proved in in vivo investigations performed on test animals.

A compact photoluminescence (PL)-based O2 sensor utilizing an organic light emitting device (OLED) as the light source is described. The sensor device is structurally integrated. That is, the sensing element and the light source, both typically thin films that are fabricated on separate glass substrates, are attached back-to-back. The sensing elements are based on the oxygen-sensitive dyes Pt- or Pd-octaethylporphyrin (PtOEP or PdOEP, respectively), which are embedded in a polystyrene (PS) matrix, or dissolved in solution. Their performance is compared to that of a sensing element based on tris(4,7-diphenyl-l,10-phenanthroline) Ru II (Ru(dpp)) embedded in a sol-gel film. A green OLED light source, based on tris(8-hydroxy quinoline Al (Alq3), was used to excite the porphyrin dyes; a blue OLED, based on 4,4'-bis(2,2'-diphenylviny1)-1,1'-biphenyl, was used to excite the Ru(dpp)-based sensing element. The O2 level was monitored in the gas phase and in water, ethanol, and toluene solutions by measuring changes in the PL lifetime tau of the O2-sensitive dyes. The sensor performance was evaluated in terms of the detection sensitivity, dynamic range, gas flow rate, and temperature effect, including the temperature dependence of tau in pure Ar and O2 atmospheres. The dependence of the sensitivity on the preparation procedure of the sensing film and on the PS and dye concentrations in the sensing element, whether a solid matrix or solution, were also evaluated. Typical values of the detection sensitivity in the gas phase, S(g) identical with tau(0% O2)/tau(100% O2), at 23 degrees C, were approximately 35 to approximately 50 for the [Alq3 OLED[/[PtOEP dye] pair; S(g) exceeded 200 for the Alq3/PdOEP sensor. For dissolved oxygen (DO) in water and ethanol, S(DO) (defined as the ratio of tau in de-oxygenated and oxygen-saturated solutions) was approximately 9.5 and approximately 11, respectively, using the PtOEP-based film sensor. The oxygen level in toluene was measured with PtOEP dissolved directly in the solution. That sensor exhibited a high sensitivity, but a limited dynamic range. Effects of aggregation of dye molecules, sensing film porosity, and the use of the OLED-based sensor arrays for O2 and multianalyte detection are also discussed.

A bacterial sensor system based on Methylomonas flagellata AJ 3670 is described for methane determinations. The system consists of a bacterial, reactor, a reference reactor and two oxygen sensors. The current decreases with time until a steady state is reached within 30 s at 30°C; the maximum current difference is obtained at 30°C and pH 7.2. The response time for the determination of methane is less than 1 min. A linear relationship is obtained between the current difference and the methane concentration below 6.6 mM; the lower limit of determination is 5 μM, and the current decrease is reproducible within 5%. The current output of the sensor is almost stable for more than 10 days and 250 assays.

A two-fluorophore system consisting of pyrene as donor and perylene as energy acceptor undergoes efficient energy transfer when pyrene is electronically excited. The excitation wavelength was that of pyrene and fluorescence was monitored at the emission wavelength of perylene. The fluorescence of pyrene is strongly quenched by oxygen, but that of perylene is not. The two-fluorophore system, in contrast, is very strongly quenched, with a 4-fold increase in the Stern-Volmer quenching constant as compared to the quenching of pyrene, as a result of the effect of oxygen on the formation of the donor-acceptor exciplex, and quenching by oxygen. The results are used to design a fluorescence-based optical oxygen sensor which offers a sensitivity greatly exceeding that of existing oxygen probes.

Microbial sensors based on oxygenn and carbon dioxide electrodes coupled with immobilized Saccharomyces are compared for measurements of glucose and other carbohydrates. With the oxygen sensor, the yeast works under aerobic conditions but anaerobically with the carbon dioxide sensor. The two metabolisms of the same strain make little difference to the lifetimes (> 15 days), selectivities and response rates (5–10 min) of the sensors. The effects of pH are very different owing to the pH sensitivity of the carbon dioxide sensor. The viable concentration ranges overlap; the oxygen-based sensor is more useful for low concentrations of glucose (0.01–1 mmol l −1 ) while the carbon dioxide-based sensor is better suited for 1–10 mmol l −1 . With the oxygen-based sensor, the response time is governed by the rate of metabolism; with the carbon dioxide-based sensor, the response time of the potentiometric carbon dioxide electrode is the rate determining step.

In constrast to existing fluoresensors for oxygen, a sensor is described that measures the decay time of the indicator rather than its emission than its emission intensity. A simple opto-electronic device is described for measuring lifetimes of a long-lived fluorophore with a frequency-modulated LED as light source. Measurement of lifetime provides as more linear Stern-Vomer plot and offers certain advantages with respect to the performance of the sensor, because it has an internal reference system that is an attractive to the frequently-used two-wavelenght referencing method. Long-term stability is distinctly better because the phase shift is independent of indicator bleaching and leaching a well as lamp intensity fluctuations. The detection limit is ca. 2 torr of oxygen.

A small-volume cell has been constructed for amperometric flow measurements with a Clark oxygen sensor and its performance was tested. The Clark sensor can be combined with immobilized enzymes for determination of substances after enzymatic conversion during which oxygen is consumed or released. Two enzymes, glucose oxidase and tyrosinase, were used and two measuring techniques, employing the enzyme immobilized on the Clark sensor membrane and with the enzyme bound on a support in a preceding reactor, were tested and compared. It was found that, in the given system, measurement with the enzyme immobilized on the sensor membrane has better sensitivity, precision and response rate.

Electrode Probes Biosensors: Challenges for the 1990's Carrier Based Sensors Development and Applications of Amperometric Biosensors Some New Enzyme Electrodes Amplification and Switching By Enzymes in Biosensors Development of High Sensitive Amperometric Enzyme Electrodes New Trends on Modified Electrodes Used in the Biomedical and Pharmaceutical Field Chemically Modified Electrodes as Biosensors: Amperometric Glucose Sensor for Flow Injection Analysis Enzyme Electrodes: From the Self-Contained Probe to the Design of an Automatic Analyzer Mammalian Cell Culture Process Control: Sampling and Sensing Biosensors for Continuous 'ex-vivo' Determination in Conjunction with an Artificial Pancreas Implantable Glucose Sensor_Problems Awaiting Solutions for Long-Term Clinical Application Flow Injection Analysis FIA_A Novel Tool for Biotechnology and Sensor Development Flow Systems for the Simultaneous Concentration Control of Different Substrates During Fermentation Bioreactor System for Clinical Analysis New Sensors Immunoprobes Enzyme Immunoassay with Electrochemical Detection in Flow Systems Possibilities for Biosensors Based on Neuroreceptors Immunosensor Systems Using Liposomes and Planar Lipid Bilayer Membranes for Ion-Channel Model Sensors Transduction of the Chemireceptor-Effector Interaction at Langmuir-Blodgett Films and Membranes Solid State Sensors Based on Chemical Modulation of Admittance of Biological Membranes Transistor Devices Novel Biosensor Systems for Clinical and Food Analysis Using Micro Devices Research and Development of FET-Based Biosensors at the Twente University of Technology Electrochemical Sensors Fabricated by Microelectronic Fabrication Processes for the Development of Biosensors Recent Development of Biosensors Based on Thermistors and Semiconductors Piezo-Optical Sensors Use of Protein Coatings on Piezoelectric Crystals for Assay of Gaseous Pollutants Fiber-Optic Sensors for Chemical Parameters of Interest in Biotechnology Fluorescence-Based Optochemical Sensors (Optodes) and Related Biosensors Using Enzyme-Catalyzed Biochemical and Antibody-Linked Immunological Reactions Photochemical Biosensors Development of Biosensors Using Optical Fibers Optical Ion Detection via Ion Pairing Fiber Optic Oxygen Sensor ''Horizon Lectures'' Engineering Proteins for Biosensor Applications Human Frontier-Science Program Bacterial Rhodopsins and Their Potential Use in Biotechnology Posters.