Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/403—Cells and electrode assemblies
  • G01N27/404—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors

Definitions

• This invention relates to an electrochemical device for determining oxygen concentration on biological surfaces.
• the sensors have not been satisfactorily designed with multiple independent sensing capacity capable of close physical contact with the surface. The latter is required for determining oxygen across nonuniform shaped surfaces.
• FIGURE 1 is a top plan view of a transparent multi-oxygen sensor
• FIGURE 2 is an enlargement of the sensor array encircled in broken line in FIGURE 1;
• FIGURE 3 is an enlarged sectional view taken on line 3-3 of FIGURE 2.
• the transparent multi-oxygen sensor array is fabricated on a suitable transparent substrate that will form the support base on which the electrodes are deposited.
• the size of the support base is dictated by the area over which an oxygen gradient is sought to be measured, and not by electrochemical considerations.
• a variety of transparent materials can be used as a support base. Particularly useful are glass or clear plastic, an example of suitable plastic being certain polymers of chlorinated hydrocarbons such as polyvinylidine chloride.
• Flexible plastic is preferred in those instances where the sensor is utilized to measure oxygen gradients across the surface of irregularly shaped tissues or organs to insure contact of the sensor with the surfaces under consideration.
• a second step is required preparatory to depositing metals on glass to insure sufficient bonding of the metals to a glass base.
• etch glass particularly useful is exposure of glass to a mild acid solution.
• suitable acids are hydrochloric acid or acetic acid.
• the multi-oxygen sensor array is accomplished by depositing, onto one side of the base, under vacuum, noble metals such as platinum or gold routinely used to construct an oxygen sensor.
• noble metals such as platinum or gold routinely used to construct an oxygen sensor.
• the multi-oxygen sensor array will have at a minimum three types of electrodes. These are oxygen-sensitive electrodes made of a noble metal, a counter electrode also composed of a noble metal, and a reference silver-silver chloride electrode. It is sometimes convenient to combine the counter and reference electrodes into a single electrode.
• the sensor base support is made of glass, it is desirable to deposit an adhesion layer of another metal before depositing the electrode metal, platinum or gold, so as to enhance the binding of the noble metal to the base.
• Illustrative of a glass-binding metal is chromium.
• Examples of such deposition techniques are vapor deposition, or sputtering.
• a layer of noble metal about 100 to about 800 angstroms thick is similarly deposited on top of the layer of chromium, and the materials heated between 250°C to 300°C for 4 to 5 hours to anneal the layers.
• Photolithographic procedures are then employed to establish the electrode pattern.
• the base is coated using procedures well-known in the art with positive photoresist material on the side containing the metal layers, and soft- baked at 90°C for 25 minutes.
• positive photoresist material is polyphenolformaldehyde resin, commercially known as novolak resin (e.g., Shipley 1350).
• novolak resin e.g., Shipley 1350
• the material is coated over the metal layers by spin coating.
• a lithographic mask suitable for forming the desired number of platinum electrodes in a particular array, and of a particular diameter, and with sufficient distance between the electrodes is positioned over the base and the plate exposed to ultraviolet light for 25 seconds. The mask is removed and the base is exposed to developer for 40 minutes followed by hard-baking at 120°C for 30 minutes.
• the oxygen electrodes are then formed by etching away the platinum and chromium layers. This can be achieved by contacting the base with a dilute mixture of hydrochloric and nitric acids (aqua regia) to etch platinum, followed by a solution of nitric acid and ceric ammonium nitrate to etch chromium.
• aqua regia hydrochloric and nitric acids
• Electrode number While there is no one combination of either electrode number, electrode diameter, or distance between electrodes that is optimally preferred for adequate performance of the sensor array, it is anticipated that more than a dozen platinum electrodes with diameters of 20>u to lO i, and 40u to 200/1 separation distance will often be employed. It is anticipated that these parameters will be a function of the type of surface and the distance over which an oxygen gradient is sought to be measured.
• the procedures used to form the platinum oxygen-sensing measuring electrodes are also employed to form the silver- silver chloride reference electrode.
• a second deposition of chromium is done using a physical mask to define the area of the intended reference electrode, followed by deposition of silver.
• Silver is deposited by vapor deposition, sputtering, or other suitable techniques.
• the layers are annealed by heating at 170°C for 2 hours.
• the base is again covered with a positive photoresist layer, and soft-baked at 90°C for 25 minutes.
• a lithographic mask having a negative image of the silver electrode is placed over the base and the base exposed to ultraviolet light for 25 seconds.
• the mask is removed and the base contacted with developer for 40 seconds followed by hard-baking at 120°C for 30 minutes.
• silver is vapor deposited and the photoresist layer is dissolved, leaving the silver electrode pattern.
• the silver is chlorided by electrochemical deposition of chloride from a solution of potassium chloride.
• Adequate performance of the sensor requires that the silver reference electrode and counter electrode occupy a particular position on the sensor base.
• the silver reference electrode must be located between the oxygen sensing electrode array and the counter electrode, preferably closer to the oxygen sensing electrodes. If a combination counter/reference electrode is used, the common electrode may be a silver-silver chloride electrode.
• the platinum sensing electrode, the silver reference electrode, and the platinum counter electrode communicate with recording instrumentation through electrical connectors by way of platinum bonding pads, which were formed during the initial deposition of platinum.
• the bonding pads are situated at the edge of the plate with each electrode being connected to a separate pad, and the pads, in turn, are connected to electrical connectors.
• the size of the bonding pad can be varied without affecting sensor performance. A satisfactory size is approximately 200 ⁇ square.
• the electrical connectors can be composed of a variety of metals well-known to the those in the art; particularly useful are platinum or gold.
• the electrical connectors can be bonded to the bonding pads by several techniques, including ultrasonic bonding, or by applying electrically conductive epoxy to the pads.
• Electrodes The base and all electrodes and connectors contained thereon are coated with photoresist material. This layer acts as an insulator to prevent oxygen from contacting metal surfaces other than those required to detect the presence of oxygen. While photoresist material is a convenient insulator, a variety of other insulating materials can also -8-
• a thickness of lu of insulating layer performs satisfactorily.
• Application of the photoresist material is achieved by covering the base containing thereon electrodes and electrical connectors with a lithographic mask to define the active electrode areas. The base is then exposed to ultraviolet light for 25 seconds, and contacted with developer to expose the areas of the electrodes that are used to detect oxygen. Lastly, the electrical connectors are connected to more substantial lead wires that connect into a multichannel recording instrument.
• a transparent multi-oxygen sensor array determines oxygen present at the surface of biological surfaces by diffusion of oxygen present through a thin layer of physiological fluids that bathe the surface. Because the sensor electrodes must be in contact with an electrolytic solution to function, and since physiological fluids are high in electrolytes, the sensor can function with the electrodes in direct contact with the fluid. However, in those instances where it is necessary, or desirable, to monitor oxygen concentration over a long period of time, it is sometimes seen that prolonged contact of the electrodes with substances present in bodily fluids may poison the - electrodes and adversely affect their performance. Thus, to minimize this the surface of the array can be covered with a membrane.
• a membrane For a membrane to be usable in this capacity, it should be permeable to oxygen, impermeable to higher molecular weight substances found in bodily fluids, and have relatively good optical properties. At a minimum, it should be partially transparent. Illustrative of materials with these properties is poly(dimethylsiloxane-carbonate) copolymer, which is sold under the trade name of MEM 213 by General Electric.
• the membrane can be attached to the sensor by a variety of methods well-known to those in the art. Particularly suitable for attachment is cyanoacrylate glue.
• the membrane must be placed over the array in such a fashion that a small quantity of conductive electrolyte is present between the membrane and the electrodes to make electrical contact.
• the transparent multi-oxygen sensor array shown in Figure 1 was tested for its ability to detect varying levels of oxygen in solution.
• the sensor was immersed in phosphate buffer, pH 7.3, at 37°C that had previously been equilibrated with atmospheric oxygen, and the resulting currents noted.
• About 50 nanoamps of current was produced for an oxygen sensor of 150/1 diameter; 30 nanoamps for a sensor 75jn diameter; and 15 nanoamps for a sensor of 25 ⁇ diameter.
• the sensor On transferring the sensor to a solution containing no oxygen, the sensor displayed a current of 1-2 nanoamps.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Molecular Biology (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
• Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)

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• 1986
  • 1986-04-11 WO PCT/US1986/000763 patent/WO1986006484A1/en unknown
  • 1986-04-11 EP EP19860902717 patent/EP0218694A1/de not_active Withdrawn
  • 1986-04-15 CA CA000506705A patent/CA1254617A/en not_active Expired

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