The present disclosure relates to sensors for measuring bioanalytes and to methods for making such sensors.
Electrochemical bio-sensors have been developed for detecting analyte concentrations in a given fluid sample. For example, U.S. Pat. Nos. 5,264,105; 5,356,786; 5,262,035; 5,320,725; and 6,464,849, which are hereby incorporated by reference in their entireties, disclose wired enzyme sensors for detecting analytes such as lactate or glucose. Technology adapted for enhancing sensor miniaturization and durability is desirable.
One aspect of the present disclosure relates to an electrochemical sensor including a sensing layer provided on an at least partially conductive fiber having a non-circular transverse cross-sectional profile.
Another aspect of the present disclosure relates to a sensor including an elongated member including at least a portion that is electrically conductive. The elongated member including a sensing layer adapted to react with a material desired to be sensed. An insulating layer surrounds the elongated member. The insulating layer defines at least one access opening for allowing the material desired to be sensed to enter an interior region defined between the elongated member and the insulating layer. The insulating layer has an inner transverse cross-sectional profile that is different from an outer transverse cross-sectional profile of the elongated member. The difference in transverse cross-sectional profiles between the elongated member and the insulating layer provides channels at the interior region defined between the insulating layer and the elongated member. The channels extend generally along the length of the elongated member and are sized to allow the material desired to be sensed to move along the length of the sensor.
A variety of additional inventive aspects will be set forth in the description that follows. The inventive aspects can relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the embodiments disclosed herein are based.
Reference will now be made in detail to exemplary aspects of the present disclosure which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
The following definitions are provided for terms used herein:
A “working electrode” is an electrode at which the analyte (or a second compound whose level depends on the level of the analyte) is electrooxidized or electroreduced with or without the agency of an electron transfer agent.
A “reference electrode” is an electrode used in measuring the potential of the working electrode. The reference electrode should have a generally constant electrochemical potential as long as no current flows through it. As used herein, the term “reference electrode” includes pseudo-reference electrodes. In the context of the disclosure, the term “reference electrode” can include reference electrodes which also function as counter electrodes (i.e., a counter/reference electrode).
A “counter electrode” refers to an electrode paired with a working electrode to form an electrochemical cell. In use, electrical current passes through the working and counter electrodes. The electrical current passing through the counter electrode is equal in magnitude and opposite in sign to the current passing through the working electrode. In the context of the disclosure, the term “counter electrode” can include counter electrodes which also function as reference electrodes (i.e., a counter/reference electrode).
A “counter/reference electrode” is an electrode that functions as both a counter electrode and a reference electrode.
An “electrochemical sensing system” is a system configured to detect the presence and/or measure the level of an analyte in a sample via electrochemical oxidation and reduction reactions on the sensor. These reactions are transduced to an electrical signal that can be correlated to an amount, concentration, or level of an analyte in the sample. Further details about electrochemical sensing systems, working electrodes, counter electrodes and reference electrodes can be found at U.S. Pat. No. 6,560,471, that is hereby incorporated by reference in its entirety.
“Electrolysis” is the electrooxidation or electroreduction of a compound either directly at an electrode or via one or more electron transfer agents.
An “electron transfer agent” is a compound that carries electrons between the analyte and the working electrode, either directly, or in cooperation with other electron transfer agents. One example of an electron transfer agent is a redox mediator.
A “sensing layer” is a component of the sensor which includes constituents that facilitate the electrolysis of the analyte. The sensing layer may include constituents such as an electron transfer agent, a catalyst which catalyzes a reaction of the analyte to produce a response at the electrode, or both. In some embodiments, the sensing layer has a generally dry or non-hydrated state prior to use. In such embodiments, the sensing layer can be hydrated during use by water within the fluid sample being tested.
Referring to
In use of the sensing system 40, the sensing tip 28 of the sensor 20 is immersed within a test volume 50 of a liquid sample (e.g., a blood sample) containing an analyte desired to be sensed. The sample may be an ex vivo or in vivo sample. The test volume 50 is the volume from which the analyte desired to be sensed can diffuse into the sensor 20 during the sensing period. With the sensor 20 so positioned, the liquid sample enters the channels 34 through the sensing tip 28 and can move along the lengths of the channels 34 (e.g., by capillary action) in a direction from the sensing tip 28 toward the base end 29. Water within the test volume 50 can diffuse into the sensing layer 24 such that the sensing layer 24 is hydrated. The analyte within the test volume 50 also diffuses into the sensing layer 24. A voltage potential is then applied between the counter electrode 48 and the working electrode. When the potential is applied, an electrical current will flow through the test volume 50 between the counter electrode 48 and the working electrode. The current is a result of the oxidation or reduction of the analyte in the test volume 50. This electrochemical reaction occurs via the electron transfer agent in the sensing layer 24 and the optional electron transfer catalyst/enzyme in the sensing layer 24. By measuring the current flow generated at a given potential, the concentration of a given analyte in the test sample can be determined. Those skilled in the art will recognize that current measurements can be obtained by a variety of techniques including, among other things, coulometric, potentiometric, amperometric, voltammetric, and other electrochemical techniques.
When the voltage potential is applied between the working and counter electrodes, the analyte within the interior region 32 reacts with the sensing layer 24 and is consumed. Thereafter, additional analyte from the test volume 50 diffuses into the interior region 32 through the open sensing tip 28. As the analyte enters the interior region 32, the analyte reacts with the portion of the sensing layer 24 located closest to the sensing tip 28 and is consumed before the analyte can migrate further into the sensor along the channels 34. In this way, the open tip configuration of the insulating layer 26 extends sensor life by limiting the amount of the sensor layer 24 that is exposed to the analyte at a given moment in time. Over time, the portion of the sensing layer 24 that is closest to the sensing tip 28 is depleted. When this occurs, the analyte is able to move further along the channels 32 (i.e., deeper into the sensor) to reach an active portion of the sensor layer 24. This process continues until the analyte depletes the sensing layer 24 along the entire lengths of the channels 34 and the life of the sensor ends. In this progression, the portion of the sensing layer 24 located at the deepest portion of the sensor (i.e., the interior region 32 closest to the base end 29) is the last portion of the sensing layer 24 to be depleted.
To oxidize or reduce the analyte, a potential (versus a reference potential) is applied across the working and counter electrodes. The minimum magnitude of the applied potential is often dependent on the particular electron transfer agent, analyte (if the analyte is directly oxidized or reduced at the electrode), or second compound (if a second compound, such as oxygen or hydrogen peroxide, whose level is dependent on the analyte level, is directly oxidized or reduced at the electrode). The applied potential usually equals or is more oxidizing or reducing, depending on the desired electrochemical reaction, than the redox potential of the electron transfer agent, analyte, or second compound, whichever is directly oxidized or reduced at the electrode. The potential at the working electrode is typically large enough to drive the electrochemical reaction to or near completion. When a potential is applied between the working electrode and the counter electrode, an electrical current will flow. The current is a result of the reduction or oxidation of the analyte or a second compound whose level is affected by the analyte. In one embodiment, the electrochemical reaction occurs via an electron transfer agent and the optional catalyst.
In certain embodiments, the elongated member 22 of the sensor 20 can include an electrically conductive wire or fiber. For example, the elongated member 22 can include a metal wire or a glassy carbon fiber. In a preferred embodiment shown at
The sensing layer 24 preferably includes a sensing chemistry such as a redox compound or mediator. The term redox compound is used herein to mean a compound that can be oxidized or reduced. Exemplary redox compounds include transition metal complexes with organic ligands. Preferred redox compounds/mediators are osmium transition metal complexes with one or more ligands having a nitrogen containing heterocycle such as 2, 2′-bipyridine. The sensing material can also include a redox enzyme. A redox enzyme is an enzyme that catalyzes an oxidation or reduction of an analyte. For example, a glucose oxidase or glucose dehydrogenase can be used when the analyte is glucose. Also, a lactate oxidase or lactate dehydrogenase fills this role when the analyte is lactate. In systems such as the one being described, these enzymes catalyze the electrolysis of an analyte by transferring electrons between the analyte and the electrode via the redox compound. Further information regarding sensing chemistry can be found at U.S. Pat. Nos. 5,264,105; 5,356,786; 5,262,035; and 5,320,725, which were previously incorporated by reference in their entireties.
The insulating layer 26 of the sensor 20 preferably serves numerous functions to the sensor 20. For example, the insulating layer 26 preferably electrically insulates the elongated member 22. Additionally, the insulating layer 26 preferably provides mechanical strength for protecting the elongated member 22. Also, as described above, the insulating layer 26 preferably forms a barrier about the elongated member 22 that prevents the uncontrolled transport of a substance desired to be sensed (e.g., an analyte such as glucose or lactate) to the sensing layer 24. In one nonlimiting embodiment, the insulating layer 26 is made of a polymeric material such as polyimide, polyurethane or other materials. In certain embodiments, the insulating layer 26 can have a maximum outer dimension (e.g., an outer diameter) less than 0.02 inches. In other embodiments, the channels 34 defined between the elongated member 22 and the insulating layer 26 can each have a transverse cross-sectional area less than or equal to 26,000 square microns. In other embodiments, the ratio of perimeter arc section (defined by the inner diameter of the insulating layer 26) to chord length (defined by a side of the elongated member 22) is about 1.2:1.
It will be appreciated that the sensor 20 can be used for ex vivo or in vivo applications. In certain embodiments, the sensor 20 can be incorporated into a peripheral catheter to provide on-line monitoring of bioanalytes in the same manner described in U.S. Pat. No. 6,464,849, that was previously incorporated by reference herein.
To manufacture sensors in accordance with the principles of the present disclosure, a conductive fiber (e.g., a Resistat(r) conductive fiber) is extruded or post-formed to have a desired cross sectional profile (e.g., triangular). As used herein, the term fiber includes threads, filaments, monofilaments, and other like elongated structures. The surface of the fiber is then cleaned (e.g., with an ultrasonic cleaner or degreaser), rinsed and dried. The surface can then be treated to improve its hydrophilic properties and/or can be activated with a plasma. Thereafter, the shaped fiber is passed through sequential coating stations by means of a reel to reel continuous process. At each station successive layers of sensor chemistry are applied uniformly as thin films and cured prior to entering the next station. The processed fiber is collected on storage reels for use in the succeeding step. Estimated process time is ˜20 feet per minute yielding ˜24,000 sub-component fibers per hour.
The cured length of fiber is collected on reels then supplied as feed stock to an assembly process where the fiber is first caused to enter a small thermoplastic molded hub (e.g., connector hub 414 of
Suitable fixtures and “pick and place” robotics can be used to intermittently feed the fiber into the short (e.g., 10 millimeter) hub and tube component, perform the cutting operation and place the completed sensor into carrier pallets for final assembly and packaging.
The various aspects disclosed herein provide numerous advantages. For example, the use of a chemically coated fiber covered by a separate insulator tube that is not adhered to the fiber allows for both structural enhancement and additional design flexibility. Also, the use of composite fiber as compared to pure glassy carbon fibers improves sensor durability and flexibility. Further, by using channels defined between the elongated member and the insulating layer, rapid hydration is possible thereby reducing the time required to activate the sensor. Further, the use of a fiber with an inert/dielectric core assists in blocking potential signal interference that might otherwise occur at the end of the fiber. Moreover, the cross sectional shape of the fiber/insulator interface profile is preferably not concentric but is of differing geometry, typically having multiple sides separated by angles (e.g., triangular, square, rectangular, pentagonal, hexagonal, etc). This configuration provides distinct multiple ports or channels which allow for providing different working electrodes associated with each port or channel. Using angular shaped fibers also provides limited points of contact around the insulator tube interior that both locate the fiber centrally within the tube—thus defining the port openings, as well as create minimal frictional contact between tube and fiber for ease of making a telescoping assembly of the two components. Limited point contacts also act as to prevent damage to the fragile chemistry coating from sliding surfaces between the fiber and the inner tube wall when mated in this fashion. The limited contact points also protect the sensor chemistry after assembly. For example, when the sensor is bent causing relative axial movement between the insulating layer and the conductive fiber, only the corners are subject to friction between the insulating layer and the fiber.
From the foregoing detailed description, it will be evident that modifications and variations can be made without departing from the spirit or scope of the broad inventive aspects embodied in the embodiments disclosed herein. For example, any of the embodiments disclosed herein can use separate reference and counter electrodes instead of combined counter/reference electrodes.
This application is a continuation of U.S. patent application Ser. No. 14/257,727, filed Apr. 21, 2014, now U.S. Pat. No. 9,459,228, issued Oct. 4, 2016, which is a continuation of U.S. patent application Ser. No. 12/674,858, filed Apr. 18, 2011, now U.S. Pat. No. 8,702,932, issued Apr. 22, 2014, which is a 371 of PCT/US2008/074644, filed Aug. 28, 2008, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/969,034, filed Aug. 30, 2007, which applications are hereby incorporated by reference in their entireties.
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Number | Date | Country | |
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20170067845 A1 | Mar 2017 | US |
Number | Date | Country | |
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60969034 | Aug 2007 | US |
Number | Date | Country | |
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Parent | 14257727 | Apr 2014 | US |
Child | 15254423 | US | |
Parent | 12674858 | US | |
Child | 14257727 | US |