Abstract: An electrodeposition and electrodialysis cell (1) having a rigid support structure (8) supporting a semipermeable membrane (9), and a number of attachments (50), each for supporting a respective electrode (7) so as to selectively vary the number and type of electrodes in the cell.

Abstract: A chemical sensor selectively detects an analyte in a solution. The sensor comprises a flow-through chamber, a selective membrane, a transducer, an inlet for a liquid flow containing a recognition element, and an outlet. To detect an analyte in a solution, a recognition element is contacted with the solution containing the analyte via a selective membrane. This results in a response detectable by a transducer. The recognition element is injected into a flow, and the flow is passed into a flow-through chamber comprising the transducer and the selective membrane, where it contacts the analyte passing from the solution outside the chamber. The recognition element and the analyte interact to provide a signal that is detected by the transducer. The chemical sensor is used for detecting analyte(s) in a reactor system, a flow system or in an in vivo system.

Abstract: The invention relates to a sensor for detecting substance concentration or activity or for determining the presence of substances based on electrochemical reactions. The electrochemical sensor comprises an electrode with surfaces inside the electrode, wherein electrochemical detection reactions occur. Said sensor guarantees high flow densities and is suitable for miniaturization. A substance-recognizing agent is advantageously placed in the electrode in contact with the inner surfaces. This enables not only short response times and long service life but also measurements with excellent linearity.

Abstract: An electrochemical gas sensor, which has a substantially more compact design and is manufactured with a considerably reduced manufacturing effort. A conical, calotte-shaped, hemispherical or cylindrical outer housing is provided with gas admission openings (3, 203). A cover (8, 208) as well as a layer structure is provided with, from the outside to the inside, the diffusion membrane (4, 204) with the electrodes (5, 6, 7; 205, 206, 207) applied thereto in a planiform manner, a layer (11, 211) consisting of a mat material or a porous body, which accommodates the electrolyte, and an electrolyte space (10, 210), which is filled at least partially with the electrolyte.

Abstract: An electrochemical sensor for detecting the presence and amount of acetate in cell culture and fermentation media. The electrochemical sensor has a pH electrode, an internal reference electrode, a special high-tensile strength gas permeable membrane, and internal reference electrolyte such that acetate concentration can be measured using a pretreatment buffer having a pH of about 5.5.

Abstract: An electrochemical gas sensor is provided which can be assembled economically and in a few steps. The electrodes (1, 2, 3) with associated electric lines are applied in a planiform manner to a membrane strip, which is impermeable to the electrolyte but permeable to gases. The membrane strip (6) is deposited in the sensor housing in a zigzag-folded pattern, so that the membrane strip limits the opening of the sensor housing for the entry of the measured gas. The electrodes (1, 2, 3) are arranged stacked in the sensor housing (5, 7) at spaced locations from one another due to the membrane strip (6) deposited in a zigzag-folded pattern.

Abstract: A compact, long-lived oxygen sensor having an aqueous electrolyte and three gas diffusion electrodes, a working electrode, a reference electrode and a counter electrode. A porous, hydrophobic means is employed in conjunction with the counter electrode to allow air pressure in the sensor to be balanced with atmospheric pressure. The working and reference electrodes are further protected from contact with flow of electrolyte from the reservoir by a separator, so that the current output is fairly independent of sensor movement.

Abstract: Disclosed is a microchip-based differential-type potentiometric oxygen gas sensor, which comprises a working electrode and a reference electrode. The working electrode is composed of a cobalt-plated electrode, a buffered hydrogel, and an ion sensitive gas permeable membrane while the reference electrode is composed of an oxygen non-sensitive silver chloride electrode and the same ion-selective gas-permeable membrane of working electrode. By taking advantage of the corrosion potential, the microchip-based oxygen gas sensor can accurately and quickly detect the content of dissolved oxygen in a sample solution. With this structure, the oxygen gas sensor is applied to a microchip-based all potentiometric multi-sensor capable of detecting two or more ions and gas species on a single chip.

Abstract: An apparatus for measuring partial hydrogen pressure in a gas stream is described. The apparatus includes a housing with micro-fuel cell sensor disposed therein. The sensor includes a sensing element having first and second gas diffusing electrodes spaced from one another with an acidic electrolyte disposed between the electrodes. A first gas permeable membrane separates the first electrode from an external gas stream. A second gas permeable membrane separates the second electrode from atmospheric air. Electrochemical charging of the first electrode occurs when hydrogen from a gas stream diffuses through the first membrane to react with the first electrode, while the potential of the second electrode remains unchanged. The potential difference between the first and second electrodes measured as current is identified to represent the sensor output.

Abstract: An electrochemical sensor system and membrane and method thereof for increased accuracy and effective life of electrochemical and enzyme sensors.

Abstract: Sensor for measuring the partial pressure of a gas in a gaseous medium, includes an electrochemical cell and a diffusion barrier with a porous membrane situated above an orifice made in a component surmounting a casing enclosing said electrochemical cell.

Abstract: A chloramine amperometric sensor includes a sensor body with an electrolyte disposed inside the sensor body. A membrane is coupled to the sensor body and adapted to pass chloramine therethrough. A reference electrode is disposed in the electrolyte and coupled to a first conductor. A second conductor is coupled to a working electrode that is disposed proximate the membrane. The working electrode is constructed from a noble metal in non-compact form. The non-compact form can be a Gas Diffusion Electrode, which can include metal mesh, carbon paper, carbon cloth, metal/carbon powder loaded on a porous membrane or any combination thereof.

Abstract: An electrochemical sensor having electrolyte, at least two electrodes and an electrolyte reservoir in a housing. The sensor has a hydrophobic gas communication means between said electrodes, electrolyte reservoir and ambient atmosphere. An electrochemical sensor having hydrophobic communication means mounted between electrodes and extending down to the electrolyte reservoir of the electrochemical sensor. Either embodiment of the sensor can provide oxygen for operation of the sensor and a balance of pressure, without interfering or poisonous gases.

Abstract: Rapid electrochemical verification of the amplification of DNA by a polymerase chain reaction in a small sample of the PCR product.

Abstract: The invention relates to gas sensors, particularly electrochemical gas sensors. The reliability of such gas sensors has been ascertained by regular tests, which involve exposing a sensor to a gas for test or calibration purposes. However, it has been difficult to provide a known quantity or concentration of gas. Another problem has been that blockage of a gas inlet has rendered the gas sensor unreliable. The invention provides a gas sensor having a self test capability and first and second electrodes, arranged so that test gas arrives at a separate instant at each electrode so as to generate two electric currents, the ratio of which currents provides an indication of the status of at least one electrode.

Abstract: A permeable protective coating for a single-ship hydrogen sensor. A hydrogen-permeable coating is applied to a semiconductor wafer containing hydrogen sensor dies, prior to dicing of the wafer. The permeable coating is preferably an organic spin-on polymer, and the hydrogen sensors preferably include hydrogen-sensing elements composed of a palladium nickel alloy.

Abstract: Electrochemical sensor for determining analyte in the presence of interferent, particularly carbon monoxide in the presence of hydrogen. An electrochemical cell is designed so that current flow resulting from reference electrode potential shift caused by interferent cancels out the current flow caused by interferent at the working electrode. Another electrochemical cell corrects for interferent concentration using the potential difference between a reference electrode in contact with interferent and a referent electrode not affected by inteferent.

Abstract: There is provided a sample preparation device and method for preparing a sample of liquid for detection of impurities. First (40) and second (38) electrodes are provided, located for immersion in a liquid under test. A semipermeable membrane (42) is positioned to protect the first electrode (40) from a body of liquid under test (32). The semipermeable membrane allows the liquid under test to pass therethrough to reach the first electrode, while preventing solids carried in the liquid from reaching the first electrode, the first electrode being positioned to affect the liquid under test in the vicinity of a sensor (36). Particular embodiments feature a hydrophilic membrane to protect the electrodes from suspended solids in the sample, a thin electrode assembly to achieve a faster response and the addition of a heater for temperature control to achieve consistent detection conditions and improved anti-fouling properties.

Abstract: This invention is directed to a method and apparatus for controlling and optimizing the feed of two or more oxidizers to an aqueous stream, thereby providing a synergistic effect. The system combines the use of amperometric or ORP based sensor technology with amperometric sensor technology employing a gas permeable membrane, thereby providing definitive control of each oxidizer feed stream.

Abstract: An insertable analyte needle sensor, comprising a set of fine wires positioned together and a dielectric material covering a substantial portion of the fine wires but defining an opening filled with at least one partially permeable membrane. The wires may be treated with a gas plasma to facilitate membrane adherence. One membrane layer may comprise sulphonated polyethersulphone coated with silane.

Abstract: An electrochemical gas sensor, which has a substantially more compact design and is manufactured with a considerably reduced manufacturing effort. A conical, calotte-shaped, hemispherical or cylindrical outer housing is provided with gas admission openings (3, 203). A cover (8, 208) as well as a layer structure is provided with, from the outside to the inside, the diffusion membrane (4, 204) with the electrodes (5, 6, 7; 205, 206, 207) applied thereto in a planiform manner, a layer (11, 211) consisting of a mat material or a porous body, which accommodates the electrolyte, and an electrolyte space (10, 210), which is filled at least partially with the electrolyte.

Abstract: An electrochemical gas sensor (1) is disclosed with a plurality of electrodes (2, 3, 4). The sensor has substantially reduced cross sensitivity with respect to interfering gases. At least the measuring electrode (2) is provided as a thin layer of diamond-like carbon (DLC, diamond-like carbon) on the gas-permeable membrane (9).

Abstract: An electrochemical gas sensor is provided which can be assembled economically and in a few steps. The electrodes (1, 2, 3) with associated electric lines are applied in a planiform manner to a membrane strip, which is impermeable to the electrolyte but permeable to gases. The membrane strip (6) is deposited in the sensor housing in a zigzag-folded pattern, so that the membrane strip limits the opening of the sensor housing for the entry of the measured gas. The electrodes (1, 2, 3) are arranged stacked in the sensor housing (5, 7) at spaced locations from one another due to the membrane strip (6) deposited in a zigzag-folded pattern.

Abstract: A dissolved oxygen sensor having a cathode and anode immersed in an electrolyte is designed to provide a low background current in the sensor when a potential is applied to the cathode. The background current is maintained at a desired level by selecting the area and length of a channel or path of diffusion of residual oxygen in the electrolyte to the cathode. The area (A) of the diffusion channel in relation to its length (L) is selected to be at or below a selected ratio, A/L.

Abstract: A sensor probe is disclosed which can measure the hydrogen peroxide content of a single sample using two oxygen sensors whose electrodes are encased in defined membranes. The oxygen reference sensor is encased in a hydrophobic membrane which prevents the transport of hydrogen peroxide or electrochemical poisons or interferents and isolates the electrodes and an electrolyte fluid surrounding the electrodes from the sample fluid. The hydrogen-peroxide-generated oxygen (HPGO) sensor is also is encased in such a hydrophobic membrane, but has in series with and distally of the hydrophobic membrane a hydrophilic membrane which contains an immobilized enzyme such as catalase, peroxidase or other enzymes of a family which catalyzes the reaction of hydrogen peroxide to oxygen and water. At the HPGO sensor, the hydrogen peroxide is catalyzed to oxygen by the enzyme so that the HPGO sensor measures an enhanced concentration of oxygen relative to the oxygen reference sensor.

Abstract: The present invention provides a novel biosensor for the detection of chemicals of interest. The novel biosensor of the present invention comprises an electrode having a catalytically active cyclodextrin attached thereto. The present invention will be useful for the detection of materials in a wide variety of samples. In particular, the present invention will permit the detection of nitrophenyl esters.

Abstract: A method and system for determining dissolved oxygen is disclosed. One or more constant currents are driven through amperometric-type dissolved oxygen probes to develop reference electrode potentials defining the envelope of oxygen electrochemistry. The reference electrode voltage is generally measured at a first current level and at a second current level utilizing the oxygen probe, wherein the first and second current levels define limitations of oxygen electrochemistry. An optimum electrode bias voltage can thereafter be automatically calculated based the reference electrode voltage measured at the first current level and the second level to thereby provide accurate indications of dissolved oxygen thereof.

Abstract: An electrochemical sensor for detection of a gas in an atmosphere containing the gas. The sensor has a housing having an electrochemical gas sensor with an electrolyte and at least two electrodes, one electrode being a gas sensing electrode. The housing has an orifice between the sensing electrode and the atmosphere for transmission of gas from the atmosphere to the sensing electrode, the orifice being protected by a hydrophobic membrane, and connected to at least two radial channels extending from the orifice. Each of the radial channels is connected to a common channel, such that gas communication from the atmosphere through the orifice to the sensing electrode is through the common channel and the radial channels, in addition to the covering membrane if the membrane is gas permeable.

Abstract: An electrochemical measuring cell for detecting hydrocyanic acid is improved in such a manner that a stable measurement signal is provided after a short time. The measuring cell includes a measuring electrode (1) of sintered gold and a counter electrode (2). A measuring cell housing (4) accommodates the measuring electrode (1) and the counter electrode (2). An electrolyte is in the measuring cell housing (4) and includes sulphuric acid with an additive of silver sulphate. A diffusion membrane (5) is disposed between the measuring electrode (1) and the substance to be detected.

Abstract: The present invention relates to a membrane for use in detecting the presence of an analyte. The membrane comprises an array of closely packed self-assembling amphiphilic molecules and a plurality of first and second receptor molecules, the first receptor molecules being reactive with one site on the analyte and second receptor molecules being reactive with another site on the analyte. The first receptor molecules are prevented from lateral diffusion within the membrane whilst the second receptor molecules are free to diffuse laterally within the membrane. The membrane is characterized in that the ratio of first receptor molecules to second receptor molecules is 10:1 or greater.

Abstract: A reference electrode (1) for electrochemical measurements includes a metallic palladium-containing electrode component (3) which is covered by a layer (4) formed of or containing a palladium compound poorly soluble in aqueous media. Positioned on layer (4) is a reference electrolyte (5) which contains anions of this palladium compound in dissolved form (FIG. 4).

Abstract: The inventive prove (10) for taking samples of an analyte located in the fluid medium has a membrane which closes the probe (10) to the outside and which is permeable to the analyte, a flow-through cell which is configured behind the membrane, a probe part (14) with at least one incoming line and one outgoing line leading to or from the flow-through cell, and a membrane holder (160) which, together with the membrane, forms a replaceable unit of the probe part (14) together with the incoming line and outgoing line.

Abstract: A combined toxic gas sensor and an oxygen sensor includes a sensor body 1 with a top plate 2 provided with a toxic gas diffusion barrier 3 leading to a chamber 7 from having an outlet aperture 5 registering with the diffusion barrier 6 of the oxygen sensor.

Abstract: A gas sensor including a housing containing at least a sensing electrode, a counter electrode, a test electrode, and electrolyte means in contact with such electrodes. The housing permits gas from the environment to flow to the sensing electrode. The gas sensor is operable either in a normal mode of operation in which potentials are applied to the electrodes for detecting when a gas to be sensed is present at the sensing electrode, or in a test mode of operation in which potentials are applied to the electrodes so that the test electrode generates a gas which flows to the sensing electrode to enable an indication whether the sensor is operating correctly.

Abstract: Systems, including apparatus and methods, for performing electrophysiological measurements on membranous samples, including living cells, isolated cell fragments (such as organelles), and/or artificial membranes (such as vesicles). The apparatus may include a high-throughput electrophysiological measurement system, and components thereof. This measurement system may include, among others, (1) a fluidics head for transferring samples and/or other compounds to a perforated measurement substrate, (2) a pressure-regulated plenum system for positioning samples on the substrate and subsequently forming a high-resistance electrical seal, (3) an activation system (such as a computer-controlled pulsed UV illumination module) for activating caged compounds, (4) an electronics head for applying and/or measuring voltage and/or current, and/or (5) a computer-controlled analysis system for collecting and/or analyzing data.

Abstract: A membrane for a sensor, a method for the preparation thereof, a layered membrane structure and a sensor for analytical measurements which require controlled analyte permeability. The membrane, layered structure and sensor may be used for biological, physiological and chemical measurements, however, are especially applicable for electrochemical measurements of glucose, lactate, urea and creatinine. The membrane comprises at least one polymer material, at least one surfactant, and at least one hydrophilic compound in admixture to provide a membrane structure in which micelles of hydrophilic compound lined with thin layers of surfactant are randomly distributed in the bulk polymer of the membrane. Upon conditioning of the membrane a structure of a percolating network of pores lined with surfactant is formed which has excellent permeability properties. The membrane has the additional advantage of a proper adhesion to polymer encapsulant structures.

Abstract: A molecular recognition sensor system for detecting the presence and concentration of an analyte including a resistive sensor having a semiconductive polymer film which swells when exposed to an analyte and interferents and a molecular imprinted resistive sensor having a semiconductive polymer film imprinted with the analyte which thereby swells when exposed to interferents, a circuit connected to the resistive sensor and the molecular imprinted resistive sensor for detecting a change in the resistance of the resistive sensor when exposed to the analyte and the interferents, the change in the resistance of the molecular imprinted resistive sensor when exposed to the analyte and interferents, and for subtracting the change in resistance of the molecular imprinted resistive sensor from the change in resistance of the resistive sensor to reduce the effect of any interferents on the change in resistance of the resistive sensor thereby determining the presence and concentration of the analyte.

Abstract: Novel membranes comprising various polymers containing heterocyclic nitrogen groups are described. These membranes are usefully employed in electrochemical sensors, such as amperometric biosensors. More particularly, these membranes effectively regulate a flux of analyte to a measurement electrode in an electrochemical sensor, thereby improving the functioning of the electrochemical sensor over a significant range of analyte concentrations. Electrochemical sensors equipped with such membranes are also described.

Abstract: A manufacturing method and sensors produced by that manufacturing method including an integrated assembly test and validation procedure benefiting from a central control. The use of the same gas supply for each stage of the manufacturing process and for research, each sensor produced by the process is labelled and is provided with access to information pertaining to that individual sensor and/or the batch within which that sensor was made. A system validation procedure deconstruct systematic errors in different parts of a gas supply system.

Abstract: Disclosed is a method for fabricating biosensors, using hydrophilic polyurethane. Bio-active reagents, including enzymes, antibodies, antigens, cells and receptors, are mixed with hydrophilic polyurethane and the mixture is directly coated over a signal transducer to form a sensing film which serves as a signal detector. The method using hydrophilic polyurethane allows the simplification of the fabrication of biosensors without conducting complicated chemical reactions and washing steps, such as crosslinking. The bio-active reagent entrapped within the hydrophilic polyurethane film can retains its high activity for an extended period of time and the intrinsic potentiometric response of the underlying ion-selective polymeric membrane is not affected by the bio-active reagent immobilized polyurethane film coated on its sensing surface. Therefore, the biosensors are superior in specificity, selectivity, and stability.

Abstract: An adapter (1) and electrochemical gas sensor (2) is provided with an electrochemical gas sensor housing (14) accommodating an electrolyte (13), with at least one measuring electrode (12) arranged therein and with a membrane (11), which screens the measuring electrode (12) from a measured gas and is permeable to the measured gas. The measuring sensitivity of an electrochemical gas sensor is increased by the adapter (1) having a gas-impermeable surface (15) extending in parallel to and at a spaced location from the membrane (11). The adapter (1) and the membrane (11) form a flow gap (10) for the measured gas delivered by a pump. The adapter (1) may be plugged onto the electrochemical sensor (2) at its outer edge (1a). The measured gas enters through a central opening (17) , expands in the flow gap (10) radially to the outside and leaves same via the ring-shaped gap (16).

Abstract: An apparatus for measuring hydrogen content and partial hydrogen pressure in gas streams and a method of modeling the sensor based on the characteristics of the sensor. The apparatus includes a housing with micro-fuel cell sensor disposed therein. The sensor includes a sensing element having first and second gas diffusing electrodes spaced from one another with an acidic electrolyte disposed between the electrodes. A first gas permeable membrane separates the first electrode from an external gas stream. A second gas permeable membrane separates the second electrode from atmospheric air. Electrochemical charging of the first electrode occurs when hydrogen from a gas stream diffuses through the first membrane to react with the first electrode, while the potential of the second electrode remains unchanged. The potential difference between the first and second electrodes measured as current is identified to represent the sensor output.

Abstract: The invention relates to an electrochemical gas sensor with a working electrode, which is designed as a thin-film electrode, and at least one counterelectrode, which are in electrical contact via an electrolyte. The electrochemical gas sensor is characterized in that the electrolyte is alkaline and preferably comprises a solution of a salt of a weak acid. The electrochemical gas sensor according to the invention may preferably be used to determine the oxygen concentration in a gas mixture.

Abstract: A sensor module for monitoring chemical properties of oil well fluids comprises at least one electrochemical sensor for a chemcal species, for example to detect pH and chloride ion concentration. A micro-porous barrier separates the electrochemical sensors from the environment of the module, the micro-porous barrier being of a material which is readily wetted by water. Periodic application of a current pulse between the barrier and a counter electrode enables fouling material to be removed from the micron barrier.

Abstract: A method and apparatus for the manipulation of colloidal particulates and biomolecules at the interface between an insulating electrode such as silicon oxide and an electrolyte solution. Light-controlled electrokinetic assembly of particles near surfaces relies on the combination of three functional elements: the AC electric field-induced assembly of planar aggregates; the patterning of the electrolyte/silicon oxide/silicon interface to exert spatial control over the assembly process; and the real-time control of the assembly process via external illumination. The present invention provides a set of fundamental operations enabling interactive control over the creation and placement of planar arrays of several types of particles and biomolecules and the manipulation of array shape and size. The present invention enables sample preparation and handling for diagnostic assays and biochemical analysis in an array format, and the functional integration of these operations.

Abstract: The invention provides an electrochemical sensor system for measuring analyte concentrations in a fluid sample. The invention is particularly useful for measuring analytes such as glucose in a patient. An implantable glucose sensor includes a disc-shaped sensor body containing multiple anodes on opposing sides of the sensor body. Electrodes including an anode and a cathode are connected to a transmitter which transmits radio signals to an external receiver and computer where data is processed to yield glucose concentration figures. An enzyme layer coating the anodes specifically reacts with glucose to increase signals generated by the anodes in response to the presence of glucose. In an alternate embodiment, some of the anodes are coated with the enzyme to generate a first signal, and other anodes that are not coated generate a second signal for comparison with the first signal to eliminate effects of interfering substances on the accuracy of the glucose measurement.

Abstract: A gas sensor is described which is particularly well suited as a carbon monoxide (CO) sensor in a self test gas sensor. The sensor includes a number of aspects which may or may not be used in conjunction with one another. A first aspect is an embodiment which reduces electrical interference (or cross-talk) between a test or gas generating cell and a sensing cell. In one embodiment, baffles are provided to prevent cross-talk. In another embodiment a switching circuit ensures that a test gas generator is operational only when the gas sensor is disconnected from a current source. A second aspect is an embodiment which includes an improved wick which is in close proximity with an electrode and ensures electrolyte is always in contact with the electrode. In an alternate embodiment a solid polymer electrolyte is used between the electrodes. A third aspect is an improved catalyst which reduces the reaction energy and thereby renders the sensor more sensitive. The catalyst is also cheaper than platinum.

Abstract: A device for monitoring an analyte is described, which includes (a) a support having an interior surface and an exterior surface; (b) a substrate connected to the interior surface of the support; (c) a spacer connected to the interior surface of the support and encompassing the substrate; and (d) a first membrane, permeable to the analyte, having an interior surface and an exterior surface, the interior surface being connected to the spacer. A chamber that encloses the substrate is defined by the interior surface of the support, the spacer, and the interior surface of the first membrane. The spacer exceeds the substrate in elevation such that a void volume exists between the interior surface of the first membrane and the substrate. A method of using the device for the transdermal monitoring of an analyte is also described.

Abstract: A rotating electrode configuration lowers the detection limits of polyion-sensitive membrane electrodes. Planar potentiometric polycation and polyanion-sensitive membrane electrodes were prepared by incorporating tridodecylmethylammonium chloride and calcium dinonylnaphthalene sulfonate, respectively, into plasticized PVC or polyurethane membranes, and mounting discs of such films on an electrode body housed in a rotating disk electrode apparatus of the type used in voltammetry. Due to the unique non-equilibrium response mechanism of such sensors, rotation of the polyion-sensitive membrane electrodes at 5000 rpm resulted in an enhancement in the detection limits toward heparin (polyanion) and protamine (polycation) of at least 1 order of magnitude (to 0.01 U/ml for heparin; 0.02 &mgr;g/ml for protamine) over that observed when the EMF responses of the same electrodes were assessed using a stir-bar to achieve connective mass transport.

Abstract: An apparatus for measuring hydrogen content and partial hydrogen pressure in gas streams and a method of modeling the sensor based on the characteristics of the sensor. The apparatus includes a housing with micro-fuel cell sensor disposed therein. The sensor includes a sensing element having first and second gas diffusing electrodes spaced from one another with an acidic electrolyte disposed between the electrodes. A first gas permeable membrane separates the first electrode from an external gas stream. A second gas permeable membrane separates the second electrode from atmospheric air. Electrochemical charging of the first electrode occurs when hydrogen from a gas stream diffuses through the first membrane to react with the first electrode, while the potential of the second electrode remains unchanged. The potential difference between the first and second electrodes measured as current is identified to represent the sensor output.