Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – Involving enzyme or micro-organism
Reexamination Certificate
2000-08-28
2001-09-04
Warden, Jill (Department: 1743)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
Involving enzyme or micro-organism
C204S403060, C204S550000, C205S792000, C600S346000, C600S347000
Reexamination Certificate
active
06284126
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of electrodes for electrochemical measurements, specifically electrodes used in the biomedical fields to measure concentrations of biomedically significant compounds.
BACKGROUND OF THE INVENTION
The amount of a chemical in a given volume of solution can be measured with an electrode. An electrode is the component in an electrochemical cell in contact with the electrolyte medium through which current can flow by electronic movement. Electrodes, which are essential components of both galvanic (current producing) and electrolytic (current using) cells, can be composed of a number of electrically conductive materials, e.g., lead, zinc, aluminum, copper, iron, nickel, mercury, graphite, gold, or platinum. Examples of electrodes are found in electric cells, where they are dipped in the electrolyte; in medical devices, where the electrode is used to detect electrical impulses emitted by the heart or the brain; and in semiconductor devices, where they perform one or more of the functions of emitting, collecting, or controlling the movements of electrons and ions.
The electrolyte can be any substance that provides ionic conductivity, and through which electrochemically active species can diffuse. Electrolytes can be solid, liquid, or semisolid (e.g., in the form of a gel). Common electrolytes include sulfuric acid and sodium chloride, which ionize in solution. Electrolytes used in the medical field must have a pH that is sufficiently close to that of the tissue in contact with the electrode (e.g., skin) so as not to cause harm to the tissue over time.
Electrochemically active species that are present in the electrolyte can undergo electrochemical reactions (oxidation or reduction) at the surface of the electrode.
The rate at which the electrochemical reactions take place is related to the reactivity of the species, the electrode material, the electrical potential applied to the electrode, and the rate at which the electrochemically active species is transported to the electrode surface.
In unstirred electrolytes, such as quiescent liquid solutions and gel electrolytes, diffusion is the main process of transport of electrochemically active species to the electrode surface. The exact nature of the diffusion process is determined by the geometry of the electrode (e.g., planar disk, cylindrical, or spherical), and the geometry of the electrolyte (e.g., semiinfinite large volume, thin disk of gel, etc.) For example, diffusion of electrochemically active species to a spherical electrode in a semiinfinite volume of electrolyte differs from diffusion of electrochemically active species to a planar disk electrode. At the center of the disk electrode the diffusion of the electroactive species towards the electrode is in a substantially perpendicular direction, whereas at the edges of the disk electrode the diffusion comes from both perpendicular and radial directions. The combination of these two different diffusion patterns makes the total current collected at the disk electrode.
The present invention makes use of a unique geometry of the electrode surface such that the diffusion of the electrochemically active species in the radial and axial direction gives a total signal higher than if there was only diffusion in the axial direction, thus allowing the use of a decreased surface area of the electrode surface, particularly for the case of an electrolyte of finite volume.
SUMMARY OF THE INVENTION
An electrode assembly is disclosed that includes a multicomponent working electrode subassembly comprised of a plurality of substantially physically separated working electrode surfaces (e.g., a plurality of working electrode components). When surfaces of the working electrode subassembly are configured over an area that is equal to the area of a single piece working electrode, the multicomponent electrode will provide an improved signal to noise ratio due to reduced noise, and will provide an enhanced signal when measuring signal from a finite amount of medium over a finite amount of time. A working electrode of the invention provides a substantially discontinuous surface area in contact with a medium through which a compound will diffuse in response to a current. Noise created by the electrode material is reduced by reducing the surface area per individual working electrode surface, and the signal is enhanced by allowing diffusion to multiple working electrode surfaces via two and preferably three dimensions, e.g., (1) normal to the main surface plane, (2) normal to the length edge, and (3) normal to the width edge. By using a substantially discontinuous surface, a large number of edges are provided within the area being monitored. In the presence of edges, the flux for the species of interest is significantly higher (at the edge, due to radial diffusion) thus giving a higher overall flux over the area of interest that is greater than that if there was only diffusion directly perpendicular to the main surface plane of the electrode of interest.
The invention features an electrode subassembly comprised of interconnected electrode surfaces that form a working electrode, with each of the electrode components being separated from the others by an electrically insulating gap.
An object of the invention is to provide a working electrode comprised of substantially discontinuous working electrode surfaces or components and thereby obtain signal from three dimensions which provide an improved signal to noise ratio.
Another object is to provide a method for measuring an electrochemical signal by providing substantially discontinuous working electrode surfaces or components that detect the flux of the electrochemical signal in two or more preferably three directions relative to the working electrode surface.
Another object of the invention is to provide an electrode subassembly composed of a working electrode comprised of substantially discontinuous working electrode surfaces for use with an electrode assembly to measure accurately, consistently, and quickly a diffused electrochemical signal, and achieve an accurate measurement of the electrochemical signal within a matter of seconds to minutes.
Another object of the invention is to provide an electrode assembly with a bonding pad or a pad that contacts a pin connector that can be readily connected and disconnected from a power source and monitoring device, thus allowing for replacement of the electrode assembly, electrode subassembly, and/or an ionically conductive material (e.g., an electrolytic gel) used with the electrode assembly.
An advantage of the working electrode is that it provides an improved signal to noise ratio by reducing noise and allowing a signal to be produced equivalent to a solid electrode but only using one half or less of the surface area of a solid electrode.
Another advantage of the invention is that the electrode can be used to measure very low concentrations of S an electrochemical signal in an electrolyte (i.e., an ionically conductive material). For example, the electrode can be used in conjunction with a hydrogel system for monitoring glucose levels in a subject (e.g., a human). An electroosmotic electrode (e.g., iontophoresis or reverse iontophoresis electrodes) can be used electrically to draw glucose into the hydrogel. Glucose oxidase (GOD) contained in the hydrogel converts the glucose into gluconic acid and hydrogen peroxide. The electrode subassembly catalyzes the hydrogen peroxide into an electrical signal. This system allows for the continuous and accurate measurement of an inflow of a very small amount of glucose in an electrolyte (e.g., glucose concentrations 10,500, or 1,000 or more times less than the concentration of glucose in blood).
Another advantage is that the electrode assembly and electrode subassembly are easily and economically produced.
A feature of the electrode subassembly of the invention is that it is small and flat, having a total surface area in the range of about 0.1 cm
2
to 8.0 cm
2
. If desired, the electrode subassembly can also b
Kurnik Ronald T.
Tamada Janet
Tierney Michael
Cygnus Inc.
McClung Barbara G.
Noguerola Alex
Robins & Pasternak LLP
Warden Jill
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