Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS20050114062 A1
Publication typeApplication
Application numberUS 10/977,292
Publication dateMay 26, 2005
Filing dateOct 29, 2004
Priority dateOct 31, 2003
Also published asCA2543797A1, CA2543797C, CA2543802A1, CA2543957A1, CA2543957C, CA2543961A1, CA2544424A1, CA2551058A1, CA2551058C, DE602004004929D1, DE602004004929T2, DE602004006148D1, DE602004006148T2, DE602004021835D1, DE602004025960D1, EP1678489A1, EP1678489B1, EP1678490A1, EP1678490B1, EP1678491A1, EP1678491B1, EP1678492A1, EP1678493A1, EP1685393A1, EP1685393B1, US7618522, US7653492, US20050133368, US20050139469, US20050139489, US20050183965, US20070276621, US20100018878, WO2005045412A1, WO2005045413A1, WO2005045414A1, WO2005045415A1, WO2005045416A1, WO2005045417A1
Publication number10977292, 977292, US 2005/0114062 A1, US 2005/114062 A1, US 20050114062 A1, US 20050114062A1, US 2005114062 A1, US 2005114062A1, US-A1-20050114062, US-A1-2005114062, US2005/0114062A1, US2005/114062A1, US20050114062 A1, US20050114062A1, US2005114062 A1, US2005114062A1
InventorsOliver Davies, Robert Marshall, Damian Baskeyfield, Lynsey Whyte, Elaine Leiper
Original AssigneeDavies Oliver W.H., Robert Marshall, Baskeyfield Damian E.H., Lynsey Whyte, Elaine Leiper
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of reducing the effect of direct interference current in an electrochemical test strip
US 20050114062 A1
Abstract
This invention describes a method of reducing the effect of interfering compounds in a bodily fluid when measuring an analyte using an electrochemical sensor. In particular, the present method is applicable to electrochemical sensors where the sensor includes a substrate, first and second working electrodes, and a reference electrode and either the first and second or only the second working electrode include regions which are bare of reagent. In this invention, an algorithm is described with mathematically corrects for the interference effect using the test strip embodiments of the present invention.
Images(14)
Previous page
Next page
Claims(4)
1. A method of reducing interferences in an electrochemical sensor comprising:
measuring a first current at a first working electrode, said first working electrode being covered by a reagent layer;
measuring a second current at a second working electrode, wherein said reagent layer partially covers said second working electrode, said second working electrode having a covered area and an uncovered area; and
calculating a corrected current value representative of a glucose concentration using a ratio of said covered area to said uncovered area of said second working electrode.
2. The method of claim 1, wherein said corrected current value is calculated using the equation:
G = WE 1 - { ( A cov A unc ) × ( WE 2 - WE 1 ) }
where G is the corrected current value, WE1 is the uncorrected current density at said first working electrode, WE2 is the uncorrected current density at said second working electrode, Acov is the coated area of said second working electrode and Aunc is the uncoated area of said second working electrode.
3. A method of reducing interferences in an electrochemical sensor comprising:
measuring a second current at a first working electrode, wherein said reagent layer partially covers said first working electrode, said first working electrode having a first covered area and a first uncovered area; measuring a second current at a second working electrode, wherein said reagent layer partially covers said second working electrode, said second working electrode having a second covered area and a second uncovered area; and
calculating a corrected current value representative of a glucose concentration using a ratio of said covered area to said uncovered area of said first and said second working electrodes.
4. The method of claim 3, wherein said corrected current value is calculated using the equation:
G = WE 1 - { ( f 1 + f 2 f 2 - 1 ) × ( WE 2 - WE 1 ) } ( Eq 7 c )
where
f1 = A cov1 A unc1 ; f2 = A cov1 A unc2 ;
Aunc1 is an uncoated area of said first working electrode;
Aunc2 is an uncoated area of said second working electrode;
Acov1 is a coated area of said first working electrode;
Acov2 is a coated area of said second working electrode;
G is the corrected current value;
WE1 is the uncorrected current density at said first working electrode; and
WE2 is the uncorrected current density at said second working electrode.
Description
    PRIORITY
  • [0001]
    The present invention claims priority to the following US Provisional Applications: U.S. Provisional Application Ser. No. 60/516,252 filed on Oct. 31, 2003; U.S. Provisional Application Ser. No. 60/558,424 filed on Mar. 31, 2004; and U.S. Provisional Application Ser. No. 60/558,728 filed on Mar. 31, 2004. Which applications are hereby incorporated herein by reference.
  • RELATED APPLICATIONS
  • [0002]
    The present invention is related to the following co-pending US Applications: U.S. patent application Ser. No. ______ [Attorney Docket Number DDI-5027 USNP], filed on Oct. 29, 2004; U.S. patent application Ser. No. ______ [Attorney Docket Number DDI-5042 USNP], filed on Oct. 29, 2004; U.S. patent application Ser. No. ______ [Attorney Docket Number DDI-5064], filed on Oct. 29, 2004; U.S. patent application Ser. No. ______ [Attorney Docket Number DDI-5066], filed on Oct. 29, 2004; and U.S. patent application Ser. No. ______ [Attorney Docket Number DDI-5067], filed on Oct. 29, 2004.
  • FIELD OF THE INVENTION
  • [0003]
    The present invention is related, in general to methods of reducing the effect of interfering compounds on measurements taken by analyte measurement systems and, more particularly, to a method of reducing the effects of direct interference currents in a glucose monitoring system using an electrochemical strip having electrodes with uncoated regions.
  • BACKGROUND OF INVENTION
  • [0004]
    In many cases, an electrochemical glucose measuring system may have an elevated oxidation current due to the oxidation of interfering compounds commonly found in physiological fluids such as, for example, acetaminophen, ascorbic acid, bilirubin, dopamine, gentisic acid, glutathione, levodopa, methyldopa, tolazimide, tolbutamide, and uric acid. The accuracy of glucose meters may, therefore, be improved by reducing or eliminating the portion of the oxidation current generated by interfering compounds. Ideally, there should be no oxidation current generated from any of the interfering compounds so that the entire oxidation current would depend only on the glucose concentration.
  • [0005]
    It is, therefore, desirable to improve the accuracy of electrochemical sensors in the presence of potentially interfering compounds such as, for example, ascorbate, urate, and, acetaminophen, commonly found in physiological fluids. Examples of analytes for such electrochemical sensors may include glucose, lactate, and fructosamine. Although glucose will be the main analyte discussed, it will be obvious to one skilled in the art that the invention set forth herein may also be used with other analytes.
  • [0006]
    Oxidation current may be generated in several ways. In particular, desirable oxidation current results from the interaction of the mediator with the analyte of interest (e.g., glucose) while undesirable oxidation current is generally comprised of interfering compounds being oxidized at the electrode surface and by interaction with the mediator. For example, some interfering compounds (e.g., acetaminophen) are oxidized at the electrode surface. Other interfering compounds (e.g., ascorbic acid), are oxidized by chemical reaction with the mediator. This oxidation of the interfering compound in a glucose measuring system causes the measured oxidation current to be dependent on the concentration of both the glucose and any interfering compound. Therefore, in the situation where the concentration of interfering compound oxidizes as efficiently as glucose and the interferent concentration is high relative to the glucose concentration, the measurement of the glucose concentration would be improved by reducing or eliminating the contribution of the interfering compounds to the total oxidation current.
  • [0007]
    One known strategy that can be used to decrease the effects of interfering compounds is to use a negatively charged membrane to cover the working electrode. As an example, a sulfonated fluoropolymer such as NAFION™ may be used to repel all negatively charged chemicals. In general, most interfering compounds such as ascorbate and urate have a negative charge, thus, the negatively charged membrane prevents the negatively charged interfering compounds from reaching the electrode surface and being oxidized at that surface. However, this technique is not always successful since some interfering compounds such as acetaminophen do not have a net negative charge, and thus, can pass through a negatively charged membrane. Nor would this technique reduce the oxidation current resulting from the interaction of interfering compounds with some mediators. The use of a negatively charged membrane on the working electrode could also prevent some commonly used mediators, such as ferricyanide, from passing through the negatively charged membrane to exchange electrons with the electrode.
  • [0008]
    Another known strategy that can be used to decrease the effects of interfering compounds is to use a size selective membrane on top of the working electrode. As an example, a 100 Dalton exclusion membrane such as cellulose acetate may be used to cover the working electrode to exclude all chemicals with a molecular weight greater than 100 Daltons. In general, most interfering compounds have a molecular weight greater than 100 Daltons, and thus, are excluded from being oxidized at the electrode surface. However, such selective membranes typically make the test strip more complicated to manufacture and increase the test time because the oxidized glucose must diffuse through the selective membrane to get to the electrode.
  • [0009]
    Another strategy that can be used to decrease the effects of interfering compounds is to use a mediator with a low redox potential, for example, between about −300 mV and +100 mV (when measured with respect to a saturated calomel electrode). Because the mediator has a low redox potential, the voltage applied to the working electrode may also be relatively low which, in turn, decreases the rate at which interfering compounds are oxidized by the working electrode. Examples of mediators having a relatively low redox potential include osmium bipyridyl complexes, ferrocene derivatives, and quinone derivatives. A disadvantage of this strategy is that mediators having a relatively low potential are often difficult to synthesize, unstable and have a low water solubility.
  • [0010]
    Another known strategy that can be used to decrease the effects of interfering compounds is to use a dummy electrode which is coated with a mediator. In some instances the dummy electrode may also be coated with an inert protein or deactivated redox enzyme. The purpose of the dummy electrode is to oxidize the interfering compound at the electrode surface and/or to oxidize the mediator reduced by the interfering compound. In this strategy, the current measured at the dummy electrode is subtracted from the total oxidizing current measured at the working electrode to remove the interference effect. A disadvantage of this strategy is that it requires that the test strip include an additional electrode and electrical connection (i.e., the dummy electrode) which cannot be used to measure glucose. The inclusion of dummy electrode is an inefficient use of an electrode in a glucose measuring system.
  • SUMMARY OF INVENTION
  • [0011]
    The invention described herein is directed to a method of reducing the effects of interferences when using an electrochemical sensor to detect analytes. An electrochemical sensor which would be useable in a method according to the present invention includes a substrate, at least first and second working electrodes and a reference electrode. A reagent layer is disposed on the electrodes such that the reagent layer completely covers all of the first working electrode and only partially covers the second working electrode. In a method according to the present invention, the oxidation current generated at the portion of the second working electrode not covered by the reagent layer is used to correct for the effect of interfering substances on the glucose measurement.
  • [0012]
    The invention described herein further includes a method of reducing interferences in an electrochemical sensor, including the steps of measuring a first oxidation current at a first working electrode, where the first working electrode is covered by a reagent layer; measuring a second oxidation current at a second working electrode, where the reagent layer only partially covers the second working electrode; and calculating a corrected oxidation current value representative of a concentration of a pre-selected analyte (e.g., glucose). In this calculation, a ratio of the covered area to the uncovered area of the second working electrode is used to remove the effects of interferences on the oxidation current. More particularly, the corrected current value may be calculated using the following equation, G = WE 1 - { ( A cov A unc ) × ( WE 2 - WE 1 ) }
    where G is the corrected current density, WE1 is the uncorrected current density at the first working electrode, WE2 is the uncorrected current density at the second working electrode, Acov is the coated area of the second working electrode, and Aunc is the uncoated area of the second working electrode 2.
  • [0013]
    In one embodiment of an electrochemical strip useable in the present invention, the electrochemical glucose test strip includes a first and second working electrodes, where the first working electrode is completely covered with a reagent layer and the second working electrode is only partially covered with the reagent layer. Thus, the second working electrode has a reagent coated area and an uncoated area. The reagent layer may include, for example, a redox enzyme such as glucose oxidase and a mediator such as, for example, ferricyanide. The first working electrode will have a superposition of two oxidation current sources, one from glucose and a second from interferents. Similarly, the second working electrode will have a superposition of three oxidation current sources from glucose, interferents at the reagent coated portion, and interferents at the uncoated portion. The uncoated portion of the second working electrode will only oxidize interferents and not oxidize glucose because there is no reagent is in this area. The oxidation current measured at the uncoated portion of the second working electrode may then be used to estimate the total interferent oxidation current and calculate a corrected oxidation current which removes the effects of interferences.
  • [0014]
    In an alternative strip embodiment useable in the method according to the present invention, the electrochemical glucose test strip includes a first and second working electrodes, where the first and second working electrode are only partially covered with the reagent layer. Thus, in this embodiment both the first and second working electrode have a reagent coated portion and an uncoated portion. The first uncovered area of the first working electrode and the second uncovered area of the second working electrode are different. The oxidation current measured at the uncoated portion of the first and second working electrodes are used to estimate the interferent oxidation current for the uncoated portion and to calculate a corrected glucose current.
  • [0015]
    The invention described herein further includes a method of reducing interferences in an electrochemical sensor, including the steps of measuring a first oxidation current at a first working electrode, where the first working electrode is partially covered by a reagent layer; measuring a second oxidation current at a second working electrode, where the reagent layer only partially covers the second working electrode; and calculating a corrected oxidation current value representative of a concentration of a pre-selected analyte (e.g., glucose). In this calculation, a ratio of the covered area to the uncovered area of the first and second working electrodes is used to remove the effects of interferences on the oxidation current. More particularly, the corrected current value may be calculated using the following equation G = WE 1 - { ( f 1 + f 2 f 2 - 1 ) × ( WE 2 - WE 1 ) }
    where f1 is equal to A cov1 A unc1 ;
    f2 is equal to A cov1 A unc2 ;
    is an uncoated area of the first working electrode; Aunc2 is an uncoated area of the second working electrode; Acov1 is a coated area of said first working electrode; Acov2 is a coated area of the second working electrode; G is a corrected current value; WE1 is an uncorrected current density at the first working electrode; and WE2 is an uncorrected current density at the second working electrode.
  • BRIEF DESCRIPTION OF DRAWINGS
  • [0016]
    A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings, of which:
  • [0017]
    FIG. 1 is an exploded perspective view of a test strip according to an embodiment of the present invention;
  • [0018]
    FIG. 2 is a simplified plane view of a distal portion of a test strip according to the embodiment of the present invention illustrated in FIG. 1 including a conductive layer and an insulation layer;
  • [0019]
    FIG. 3 is a simplified plane view of a distal portion of a test strip according to the embodiment of the present invention illustrated in FIG. 1 wherein the position of a reagent layer is illustrated with the conductive layer and the insulation layer;
  • [0020]
    FIG. 4 is an exploded perspective view of a test strip according to a further embodiment of the present invention;
  • [0021]
    FIG. 5 is a simplified plane view of a distal portion of a test strip according to the embodiment of the present invention illustrated in FIG. 4 including of a conductive layer and an insulation layer; and
  • [0022]
    FIG. 6 is a simplified plane view of a distal portion of a test strip according to the embodiment of the present invention illustrated in FIG. 4 wherein a reagent layer is illustrated with the conductive layer and the insulation layer.
  • [0023]
    FIG. 7 is a simplified plane view of a distal portion of a test strip according to the embodiment of the present invention illustrated in FIG. 4 wherein a reagent layer is illustrated with the conductive layer.
  • [0024]
    FIG. 8 is a simplified plane view of a distal portion of a test strip according to another embodiment of the present invention wherein a reagent layer is illustrated with the conductive layer that helps reduce an IR drop effect.
  • [0025]
    FIG. 9 is a simplified plane view of a distal portion of a test strip according to yet another embodiment of the present invention wherein a reagent layer is illustrated with the conductive layer and the insulation layer such there are two working electrodes that have an uncoated portion.
  • [0026]
    FIG. 10 is a simplified plane view of a distal portion of a test strip according to still yet another embodiment of the present invention wherein a reagent layer is illustrated with the conductive layer and the insulation layer such there are two working electrodes that have an uncoated portion.
  • [0027]
    FIG. 11 is a graph showing the current at a first working electrode of a strip designed in accordance with the present invention tested with 70 mg/dL glucose samples in blood spiked with varying levels of uric acid.
  • [0028]
    FIG. 12 is a graph showing the current at a first working electrode at a strip designed in accordance with the present invention tested with 240 mg/dL glucose samples in blood spiked with varying levels of uric acid.
  • [0029]
    FIG. 13 is an exploded perspective view of a test strip that has an integrated lance.
  • [0030]
    FIG. 14 is a simplified schematic showing a meter interfacing with a test strip that has a first contact, second contact, and reference contact disposed on a substrate.
  • DETAILED DESCRIPTION OF THE INVENTION
  • [0031]
    This invention described herein includes a test strip and method for improving the selectivity of an electrochemical glucose measuring system.
  • [0032]
    FIG. 1 is an exploded perspective view of a test strip according to a first embodiment of the present invention. In the embodiment of the present invention illustrated in FIG. 1, an electrochemical test strip 62, which may be used for measuring glucose concentration in bodily fluids such as blood or interstitial fluid, includes a first working electrode 10 and a second working electrode 12, where first working electrode 10 is completely covered with a reagent layer 22 and second working electrode 12 is only partially covered with reagent layer 22. Thus, the second working electrode has a reagent coated portion and an uncoated portion. Reagent layer 22 may include, for example, a redox enzyme such as, for example, glucose oxidase and a mediator such as, for example, ferricyanide. Because ferricyanide has a redox potential of approximately 400 mV (when measured with respect to a saturated calomel electrode) at a carbon electrode, the introduction of a bodily fluid e.g., blood may generate a significant oxidation of interferents by the mediator and/or the working electrode. Therefore, the oxidation current measured at first working electrode 10 will be a superposition of oxidation current sources: a first, desirable, oxidation current generated by the oxidation of glucose and a second, undesirable, oxidation current generated by the interferents. The oxidation current measured at second working electrode 12 will also be a superposition of oxidation current sources: a first, desirable oxidation current generated by the oxidation of glucose, a second, undesirable oxidation current generated by interferents at the covered portion of working electrode 12 and a third oxidation current generated by interferents at the uncovered portion of working electrode 12. The uncoated portion of second working electrode 12 will only oxidize interferents and not oxidize glucose because there is no reagent on the uncoated portion of second working electrode 12. Because the oxidation current measured at the uncoated portion of second working electrode 12 does not depend on glucose and the uncoated area of second working electrode 12 is known, it is possible to calculate the interferent oxidation current for the uncoated portion of the second working electrode 12. In turn, using the interferent oxidation current calculated for the uncoated portion of second working electrode 12 and knowing the area of first working electrode 10 and the area of the coated portion of second working electrode 12, it is possible to calculate a corrected glucose current which accounts for the effects of interfering compounds oxidized at the electrode.
  • [0033]
    FIG. 1 is an exploded perspective view of a test strip 62 according to a first embodiment of the present invention. Test strip 62, as illustrated in FIG. 1, may be manufactured by a series of 6 consecutive printing steps which lay down six layers of material on substrate 50. The six layers may be deposited by, for example, screen printing on substrate 50. In an embodiment of this invention, the 6 layers may include a conductive layer 64, an insulation layer 16, a reagent layer 22, an adhesive layer 66, a hydrophilic layer 68, and a top layer 40. Conductive layer 64 may further includes first working electrode 10, second working electrode 12, reference electrode 14, first contact 11, second contact 13, reference contact 15, and strip detection bar 17. Insulation layer 16 may further include cutout 18. Adhesive layer 66 may further include first adhesive pad 24, second adhesive pad 26, and third adhesive pads 28. Hydrophilic layer 68 may further include first hydrophilic film 32, and second hydrophilic film 34. Top layer 40 may further includes a clear portion 36 and opaque portion 38. Test strip 62 has a first side 54 and second side 56, a distal electrode side 58, and a proximal electrode side 60 as illustrated in FIG. 1. The following sections will describe the respective layers of test strip 62 in more detail.
  • [0034]
    In one embodiment of the present invention, substrate 50 is an electrically insulating material such as plastic, glass, ceramic, and the like. In a preferred embodiment of this invention, substrate 50 may be a plastic such as, for example, nylon, polycarbonate, polyimide, polyvinylchloride, polyethylene, polypropylene, PETG, or polyester. More particularly the polyester may be, for example Melinex® ST328 which is manufactured by DuPont Teijin Films. Substrate 50 may also include an acrylic coating which is applied to one or both sides to improve ink adhesion.
  • [0035]
    The first layer deposited on substrate 50 is conductive layer 64 which includes first working electrode 10, second working electrode 12, reference electrode 14, and strip detection bar 17. In accordance with the present invention, a screen mesh with an emulsion pattern may be used to deposit a material such as, for example, a conductive carbon ink in a defined geometry as illustrated in FIG. 1. Reference electrode 14 may also be a counter electrode, a reference/counter electrode, or a quasi-reference electrode. Conductive layer 64 may be disposed on substrate 50 by using screen printing, rotogravure printing, sputtering, evaporation, electroless plating, ink jetting, sublimation, chemical vapor deposition, and the like. Suitable materials which may be used for conductive layer 64 are Au, Pd, Ir, Pt, Rh, stainless steel, doped tin oxide, carbon, and the like. In an embodiment of this invention, the carbon ink layer may have a height between 1 and 100 microns, more particularly between 5 and 25 microns, and yet even more particularly at approximately 13 microns. The height of the conductive layer can vary depending on the desired resistance of the conductive layer and the conductivity of the material used for printing the conductive layer.
  • [0036]
    First contact 11, second contact 13, and reference contact 15 may be used to electrically interface with a meter. This allows the meter to electrically communicate to first working electrode 10, second working electrode 12, and reference electrode 14 via, respective, first contact 11, second contact 13, and reference contact 15.
  • [0037]
    The second layer deposited on substrate 50 is insulation layer 16. Insulation layer 16 is disposed on at least a portion of conductive layer 64 as shown in FIG. 1. FIG. 2 is a simplified plane view of a distal portion of test strip 62 which highlights the position of first working electrode 10, second working electrode 12, and reference electrode 14 with respect to insulation layer 16. Insulation layer 16 further includes a cutout 18 which may have a T-shaped structure as shown in FIG. 1 and 2. Cutout 18 exposes a portions of first working electrode 10, second working electrode 12, and reference electrode 14 which can be wetted with liquid. Cutout 18 further includes a distal cutout width W1, proximal cutout width W2, a distal cutout length L4 and a proximal cutout length L5. Distal cutout width W1 corresponds to the width of first working electrode 10 and reference electrode 14 as illustrated in FIG. 2. Distal cutout length L4 corresponds to a length which is greater than both first working electrode 10 and reference electrode 14 together. Proximal cutout width W2 and proximal cutout length L5 form a rectangular section which exposes the width and length of second working electrode 12. In accordance with the present invention, distal cutout width W1, proximal cutout width W2, distal cutout length L4 and proximal cutout length L5 may have a respective dimension of approximately 0.7, 1.9, 3.2, and 0.43 mm. In one embodiment of the present invention, first working electrode 10, reference electrode 14, and second working electrode 12 have a respective length of L1, L2, and L3 which may be about 0.8, 1.6, and 0.4 mm. In accordance with the present invention, electrode spacing S1 is a distance between first working electrode 10 and reference electrode 14; and between reference electrode 14 and second working electrode 12 which may be about 0.4 mm.
  • [0038]
    The third layer deposited on substrate 50 is a reagent layer 22. Reagent layer 22 is disposed on at least a portion of conductive layer 64 and insulation layer 16 as shown in FIGS. 1. FIG. 3 is a simplified plane view of a distal portion of test strip 62 according to the first embodiment of the present invention which highlights the position of reagent layer 22 with respect to first working electrode 10, second working electrode 12, reference electrode 14, and insulation layer 16. Reagent layer 22 may be in the shape of a rectangle having a reagent width W3 and a reagent length L6 as illustrated in FIG. 1 and 3. In one embodiment of the invention, reagent width W3 may be about 1.3 mm and reagent length L6 may be about 4.7 mm. In a further embodiment of the present invention, reagent layer 22 has a sufficiently large width W3 and length L6 such that reagent layer 22 completely covers first working electrode 10 and reference electrode 14. However, reagent layer 22 has an appropriately sized width W3 and length L6 such that second working electrode is not completely covered with reagent layer 22. In such a scenario, second working electrode 12 has a coated portion 12 c and an uncoated portions 12 u as illustrated in FIG. 3. Uncoated portions 12u may be in the shape of two rectangles where uncoated portions 12 u has a wing width W4 and a length that corresponds to second working electrode length L3. As a non-limiting example, wing width W4 may be about 0.3 mm. In one embodiment of the present invention, reagent layer 22 may include a redox enzyme such as, for example, glucose oxidase or PQQ-glucose dehydrogenase (where PQQ is an acronym for pyrrolo-quinoline-quinone) and a mediator such as, for example, ferricyanide.
  • [0039]
    The fourth layer deposited on substrate 50 is an adhesive layer 66 which includes a first adhesive pad 24, a second adhesive pad 26, and a third adhesive pad 28. First adhesive pad 24 and second adhesive pad 26 form the walls of a sample receiving chamber. In one embodiment of the present invention, first adhesive pad 24 and second adhesive pad 26 may be disposed on substrate 50 such that neither of the adhesive pads touches reagent layer 22. In another embodiments of the present invention where the strip volume needs to be reduced, first adhesive pad 24 and/or second adhesive pad 26 may be disposed on substrate 50 such there is overlap with reagent layer 22. In an embodiment of the present invention, adhesive layer 66 has a height of about 70 to 110 microns. Adhesive layer 66 may include a double sided pressure sensitive adhesive, a UV cured adhesive, heat activated adhesive, thermosetting plastic, or other adhesive known to those skilled in the art. As a non-limiting example, adhesive layer 66 may be formed by screen printing a pressure sensitive adhesive such as, for example, a water based acrylic copolymer pressure sensitive adhesive which is commercially available from Tape Specialties LTD in Tring, Herts, United Kingdom (part#A6435).
  • [0040]
    The fifth layer deposited on substrate 50 is a hydrophilic layer 68 which includes a first hydrophilic film 32 and second hydrophilic film 34 as illustrated in FIG. 1. Hydrophilic layer 68 forms the “roof” of the sample receiving chamber. The “side walls” and “floor” of the sample receiving chamber are formed by a portion of adhesive layer 66 and substrate 50, respectively. As a non-limiting example, hydrophilic layer 68 may be an optically transparent polyester with a hydrophilic anti-fog coating such as those commercially obtained from 3M. The hydrophilic nature of the coating is used in the design of strip 62 because it facilitates filling of liquid into the sample receiving chamber.
  • [0041]
    The sixth and final layer deposited on substrate 50 is a top layer 40 which includes a clear portion 36 and opaque portion 38 as illustrated in FIG. 1. In accordance with the present invention, top layer 40 includes a polyester which is coated on one side with a pressure sensitive adhesive. Top layer 40 has an opaque portion 38 which helps the user observe a high degree of contrast when blood is underneath clear portion 36. This allows a user to visually confirm that the sample receiving chamber is sufficiently filled. After strip 62 is fully laminated, it is cut along incision line A-A′ and in the process creates sample inlet 52 as illustrated in FIG. 3.
  • [0042]
    The first test strip embodiment as illustrated in FIGS. 1-3 may have a possible drawback in that reagent layer 22 may dissolve in a liquid sample and move a portion of the dissolved reagent layer over the uncoated portions 12 u of second working electrode 12. If such a scenario were to occur, uncoated portions 12 u would also measure an oxidation current that is also proportional to the glucose concentration. This would degrade the ability to use mathematical algorithms for removing the effect of interferent oxidation. In an alternative embodiment of the present invention, reagent layer 22 should be designed to dissolve in such a way that it does not migrate to uncoated portions 12 u. For example, reagent layer 22 may be chemically bound to the first working electrode 10, second working electrode 12, and reference electrode 14 or may have a thickening agent that minimizes the migration of dissolved reagent layer 22.
  • [0043]
    A further embodiment of the present invention as illustrated in FIG. 4, the embodiment illustrated in FIG. 4 reduces, and in certain circumstances minimizes, the immigration of dissolved reagent to an uncoated portion of the second working electrode. In this embodiment, second working electrode 102 has a C-shaped geometry where 2 discrete portions of second working electrode 102 are exposed by cutout 108 as illustrated in FIG. 4. In accordance with the present invention, reagent layer 110 is disposed on only a portion of second working electrode 102 to form an uncoated portion 102 u and coated portion 102 c as illustrated in FIG. 6. Uncoated portion 102 u is adjacent to sample inlet 52. Coated portion 102 c is adjacent to first working electrode 100. When applying liquid to sample inlet 52 of an assembled test strip 162, the liquid will flow from sample inlet 52 to coated portion 102 c until all electrodes are covered with liquid. By positioning uncoated portion 102 u upstream of the liquid flow, this almost entirely prevents reagent layer 110 from dissolving and migrating to uncoated portion 102 u. This enables the mathematical algorithm to accurately remove the effects of interferents from the measured oxidation current.
  • [0044]
    FIG. 4 is an exploded perspective view of a test strip 162. Test strip 162 is manufactured in a manner similar to test strip 62 except that there are geometric or positional changes to a conductive layer 164, an insulation layer 106, and a reagent layer 110. For the second embodiment of this invention, substrate 50, adhesive layer 66, hydrophilic layer 68, and top layer 40 are the same as the first strip embodiment. Test strip 162 has a first side 54 and second side 56, a distal electrode side 58, and a proximal electrode side 60. It should also be noted that the first and second test strip embodiment of the present invention may have elements with similar structure which are denoted with the same element number and name. If analogous elements between the respective test strip embodiments are different in structure, the elements may have the same name, but be denoted with a different element number. The following sections will describe the respective layers of test strip 162 in more detail.
  • [0045]
    For the strip embodiment illustrated in FIG. 4, the first layer deposited on substrate 50 is conductive layer 164 which includes first working electrode 100, second working electrode 102, reference electrode 104, first contact 101, second contact 103, and reference contact 105, and strip detection bar 17. In accordance with the present invention, a screen mesh with an emulsion pattern may be used to deposit a material such as, for example, a conductive carbon ink in a defined geometry as illustrated in FIG. 4. First contact 101, second contact 103, and reference contact 105 may be used to electrically interface with a meter. This allows the meter to electrically communicate to first working electrode 100, second working electrode 102, and reference electrode 104 via, respective, first contact 101, second contact 103, and reference contact 105.
  • [0046]
    The second layer deposited on substrate 50 in FIG. 4 is insulation layer 106. Insulation layer 106 is disposed on at least a portion of conductive layer 164 as shown in FIGS. 4. FIG. 5 is a simplified plane view of a distal portion of test strip 162 which highlights the position of first working electrode 100, second working electrode 102, and reference electrode 104 with respect to insulation layer 106.
  • [0047]
    The third layer deposited on substrate 50 in FIG. 4 is a reagent layer 110 such that reagent layer 110 is disposed on at least a portion of conductive layer 164 and insulation layer 106 as shown in FIG. 6. FIG. 6 is a simplified plane view of a distal portion of test strip 162 according to the second embodiment of the present invention which highlights the position of reagent layer 110 with respect to first working electrode 100, second working electrode 102, reference electrode 104, and insulation layer 106. Reagent layer 110 may be in the shape of a rectangle having a reagent width W13 and a reagent length L16. In one embodiment of this invention, reagent width W13 may be about 1.3 mm and reagent length L16 may be about 3.2 mm. In a preferred embodiment of the present invention, reagent layer 110 has a sufficient width W13 and length L16 such that reagent layer 110 completely covers first working electrode 100, coated portion 102 c, and reference electrode 104, but does not cover uncoated portion 102 u.
  • [0048]
    FIG. 7 is a simplified plane view of a distal portion of a test strip according to the embodiment of the present invention illustrated in FIG. 4 wherein a reagent layer is illustrated with the conductive layer. In contrast to FIG. 6, FIG. 7 does not show insulation layer 106. This helps demonstrate the conductive relationship between uncoated portion 102 u and coated portion 102 c which was hidden underneath the opaque character of insulation layer 106.
  • [0049]
    For the strip embodiment illustrated in FIG. 4, insulation layer 106 is used to define the width of the first working electrode 100, second working electrode 102, and reference electrode 104. Insulation layer 106 further includes a cutout 108 which may have a T-shaped structure as shown in FIG. 4 to 6. Cutout 108 exposes a portion of first working electrode 100, second working electrode 102, and reference electrode 104 which can be wetted with liquid. Cutout 108 further includes a distal cutout width W11, proximal cutout width W12, a distal cutout length L14 and a proximal cutout length L15 as illustrated in FIG. 5 and 6. Distal cutout width W11 corresponds to the width of uncoated portion 102 u. Distal cutout length L14 is greater than the length uncoated portion 102 u. Proximal cutout width W12 and proximal cutout length L15 forms a rectangular section which approximately exposes the width and length of first working electrode 100, reference electrode 104, and coated portion 102 c.
  • [0050]
    In accordance with the present invention, distal cutout width W11, proximal cutout width W12, distal cutout length L14 and proximal cutout length L15 may have a respective dimension of approximately 1.1, 0.7, 2.5, and 2.6 mm.
  • [0051]
    In the embodiment of FIG. 4, uncoated portion 102 u, reference electrode 104, first working electrode 100, and coated portion 102 c have a respective length of L10, L12, L11, and L13 which may be about 0.7, 0.7, 0.4, and 0.4 mm. Electrode spacing S11 is a distance between uncoated portion 102 u and reference electrode 104 which may be between about 0.2 to 0.75 mm, and more preferably between 0.6 to 0.75 mm. Electrode spacing S10 is a distance between reference electrode 104 and first working electrode 100; and between coated portion 102 c and first working electrode 100 which may be about 0.2 mm. It should be noted that electrode spacing S11 is greater than S10 to decrease the possibility of reagent dissolving and migrating to uncoated portion 102 u. Additionally, electrode spacing S11 is greater than S10 to decrease the possibility of reagent layer 110 being disposed on uncoated portion 102 u because of variations in the printing process. The fourth through sixth layer which is successively disposed on strip 162 in the same manner as the first strip embodiment. The relative position and shape of the adhesive layer 66, hydrophilic layer 68, and top layer 40 are illustrated in FIG. 4.
  • [0052]
    In the embodiment of the invention illustrated in FIG. 8, the C-shape of second working electrode 102 may be partially altered so that the order in which liquid would wet the electrodes would be uncoated portion 102 u, first working electrode 100, reference electrode 104, and then coated portion 102 c. In the alternative format, first working electrode 100 and coated portion 102 c would be equidistant from reference electrode 104 which is desirable from an IR drop perspective. In the second strip embodiment (i.e. test strip 162) illustrated in FIG. 7, the electrodes are arranged so that the order in which liquid would wet the electrodes would be uncoated portion 102 u, reference electrode 104, first working electrode 100, and then coated portion 102 c. For test strip 162, coated portion 102 c is farther away from reference electrode 104 than the distance between first working electrode 100 and reference electrode 104.
  • [0053]
    An algorithm may, therefore be used to calculate a corrected glucose current that is independent of interferences. After dosing a sample onto a test strip, a constant potential is applied to the first and second working electrodes and a current is measured for both electrodes. At the first working electrode where reagent covers the entire electrode area, the following equation can be used to describe the components contributing to the oxidation current,
    WE 1 =G+I cov   (Eq 1)
    where WE1 is a current density at the first working electrode, G is a current density due to glucose which is independent of interferences, and Icov is a current density due to interferences at the portion of a working electrode covered with reagent.
  • [0054]
    At the second working electrode which is partially covered with reagent, the following equation can be used to describe the components contributing to the oxidation current,
    WE 2 =G+I cov +I unc   (Eq 2)
    where WE2 is a current density at the second working electrode and Iunc is a current density due to interferences at the portion of a working electrode not covered with reagent.
  • [0055]
    To reduce the effects of interferences, an equation is formulated which describes the relationship between the interferent current at the coated portion of the second working electrode and the uncoated portion of the second working electrode. It is approximated that the interferent oxidation current density measured at the coated portion is the same as the current density measured at the uncoated portion. This relationship is further described by the following equation, I cov = A cov A unc × I unc ( Eq 3 a )
    where Acov is the area of second working electrode covered with reagent and Aunc is the area of second working electrode not covered with reagent.
  • [0056]
    Uncoated portions 12 u can oxidize interferents, but not glucose because it is not coated with reagent layer 22. In contrast, coated portion 12 c can oxidize glucose and interferents. Because it was experimentally found that uncoated portions 12 u oxidizes interferents in a manner proportional to the area of coated portion 12 c, it is possible to predict the proportion of interferent current measured overall at second working electrode 12. This allows the overall current measured at second working electrode 12 to be corrected by subtracting the contribution of the interferent current. In an embodiment of the present invention the ratio of Aunc:Acov may be between about 0.5:1 to 5:1, and is preferably about 3:1. More details describing this mathematical algorithm for current correction will be described in a later section.
  • [0057]
    In an alternative embodiment of the present invention, the interferent oxidation current density measured at the coated portion may be different than the current density measured at the uncoated portion. This may be ascribed to a more efficient or less efficient oxidation of interferents at the coated portion. In one scenario, the presence of a mediators may enhance the oxidation of interferences relative to the uncoated portion. In another scenario, the presence of viscosity increasing substances such as hydroxyethyl cellulose may decrease the oxidation of interferences relative to the uncoated portion. Depending on the components included in the reagent layer which partially coats the second working electrode, it is possible that the interferent oxidation current density measured at the coated portion may be more or less than the uncoated portion. This behavior may be phenomenologically modeled by re-writing Equation 3 a to the following form,
    I cov =f×I unc   (Eq 3b)
    where f is a correction factor which incorporates the effects of the interferent oxidation efficiency of the coated to uncoated portion.
  • [0058]
    In an embodiment of the present invention, Equation 1, 2, and 3a may be manipulated to derive an equation that outputs a corrected glucose current density independent of interferences. It should be noted that the three equations (Equation 1, 2, and 3a) collectively have 3 unknowns which are G, Icov, and Iunc. Equation 1 can be rearranged to the following form.
    G=WE 1 −I cov   (Eq 4)
    Next, Icov from Equation 3a can be substituted into Equation 4 to yield Equation 5. G = WE 1 - [ A cov A unc × I unc ] ( Eq 5 )
    Next, Equation 1 and Equation 2 can be combined to yield Equation 6.
    I unc =WE 2 −WE 1   (Eq 6)
    Next, Iunc from Equation 6 can be substituted into Equation 5 to yield Equation 7a. G = WE 1 - { ( A cov A unc ) × ( WE 2 - WE 1 ) } ( Eq 7 a )
  • [0059]
    Equation 7a outputs a corrected glucose current density G which removes the effects of interferences requiring only the current density output of the first and second working electrode, and a proportion of the coated to uncoated area of the second working electrode. In one embodiment of the present invention the proportion A cov A unc
    may be programmed into a glucose meter, in, for example, a read only memory. In another embodiment of the present invention, the proportion A cov A unc
    may be transferred to the meter via a calibration code chip which would may account for manufacturing variations in Acov or Aunc.
  • [0060]
    In an alternative embodiment to the present invention Equation 1, 2, and 3b may be used when the interferent oxidation current density for the coated portion is different from the interferent oxidation current density of the uncoated portion. In such a case, an alternative correction Equation 7b is derived as shown below.
    G=WE 1 −{f×(WE 2 −WE 1)}  (Eq 7b)
  • [0061]
    In another embodiment of the present invention, the corrected glucose current Equation 7a or 7b may be used by the meter only when a certain threshold is exceeded. For example, if WE2 is about 10% or greater than WE1, then the meter would use Equation 7a or 7b to correct for the current output. However, if WE2 is about 10% or less than WE1, the meter would simple take an average current value between WE1 and WE2 to improve the accuracy and precision of the measurement. The strategy of using Equation 7a or 7b only under certain situations where it is likely that a significant level of interferences are in the sample mitigates the risk of overcorrecting the measured glucose current. It should be noted that when WE2 is sufficiently greater than WE1 (e.g. about 20% or more), this is an indicator of having a sufficiently high concentration of interferents. In such a case, it may be desirable to output an error message instead of a glucose value because a very high level of interferents may cause a breakdown in the accuracy of Equation 7a or 7b.
  • [0062]
    In a the embodiment of the present invention illustrated in FIG. 9 and 10, the first and second working electrodes are partially covered with the reagent layer in such a way that that the uncoated portions of the first and second working electrodes are different. This contrasts the previously described first and second test strip embodiments where the first working electrode is completely covered with the reagent layer.
  • [0063]
    FIG. 9 is a simplified plane view of a distal portion of a test strip 2000 according to yet another embodiment of the present invention wherein a reagent layer 22 is illustrated with the conductive layer and insulation layer 2002 such there are two working electrodes which have an uncoated portion. Test strip 2002 is manufactured in a manner similar to test strip 62 except that there is a geometric change to cutout 18 as shown in FIG. 1. Test strip 2002 has the same substrate 50, conductive layer 64, reagent layer 22, adhesive layer 66, hydrophilic layer 68, and top layer 40 as test strip 62. Test strip 2002 was modified to have a cutout 2004 which has a dumbbell like shape as illustrated in FIG. 9. The modified shape for cutout 2004 allows first working electrode 2008 to include a first coated portion 2008 c and an first uncoated portion 2008 u; and second working electrode 2006 to include a second coated portion 2006 c and second uncoated portion 2006 u. In order for test strip 2000 to effectively reduce the effects of interferents, the two first uncoated portions 2008 u must have a different total area than the two second uncoated portions 2006 u.
  • [0064]
    FIG. 10 is a simplified plane view of a distal portion of a test strip 5000 according to still yet another embodiment of the present invention wherein a reagent layer 820 is illustrated with the conductive layer such there are two working electrodes which have an uncoated portion. Test strip 5000 is manufactured in a manner similar to test strip 162 except that there is a geometric change to conductive layer 164 such that both a first working electrode 4002 and a second working electrode 4004 have a C-shape. Test strip 5000 has the same substrate 50, insulation layer 106, reagent layer 110, adhesive layer 66, hydrophilic layer 68, and top layer 40 as test strip 162. The modified geometry allows first working electrode 4002 to include a first coated portion 4002 c and an first uncoated portion 4002 u; and second working electrode 4004 to include a second coated portion 4004 c and second uncoated portion 4004 u. In order for test strip 2000 to effectively reduce the effects of interferents, first uncoated portion 4002 u must have a different area than second uncoated portion 4004 u.
  • [0065]
    Test strips 2000 and 5000 have an advantage in that they may be easier to manufacture in regards to depositing the reagent layer with the required registration and also any subsequently deposited layers. Furthermore, both the first and second working electrodes will have to some extent the same chemical and electrochemical interactions with any interfering substances thus ensuring greater accuracy in the correction process. With both working electrodes having some level of uncoated area the same reactions will occur on both electrodes but to a different extent. Using a simple modification to Equation 7a, the following Equation 7c can be used as the correction equation for glucose, G = WE 1 - { ( f 1 + f 2 f 2 - 1 ) × ( WE 2 - WE 1 ) } ( Eq 7 c )
    where f 1 = A cov1 A unc1 , f 2 = A cov1 A unc2 ,
    Aunc1=is an uncoated area of the first working electrode, Aunc2=is an uncoated area of the second working electrode, Acov1=is a coated area of the first working electrode, and Acov2=is a coated area of the second working electrode.
  • [0066]
    One advantage of the present invention is the ability to use the first and second working electrode to determine that the sample receiving chamber has been sufficiently filled with liquid. It is an advantage of this invention in that the second working electrode not only corrects the interferent effect, but can also measure glucose. This allows for a more accurate results because 2 glucose measurements can be averaged together while using only one test strip.
  • EXAMPLE 1
  • [0067]
    Test strips were prepared according to the first embodiment of the present invention as illustrated in FIG. 1 to 3. These test strips were tested in blood having various concentrations of interferents. To test these strips, they were electrically connected to a potentiostat which has the means to apply a constant potential of 0.4 volts between the first working electrode and the reference electrode; and the second working electrode and the reference electrode. A sample of blood is applied to the sample inlet allowing the blood to wick into the sample receiving chamber and to wet first working electrode, second working electrode, and reference electrode. The reagent layer becomes hydrated with blood and then generates ferrocyanide which may be proportional to the amount of glucose and/or interferent concentration present in the sample. After about 5 seconds from the sample application to the test strip, an oxidation of ferrocyanide is measured as a current for both the first and second working electrode.
  • [0068]
    FIG. 11 shows the current responses of the first working electrode tested with 70 mg/dL glucose samples in blood spiked with varying levels of uric acid. The uncorrected current at the first working electrode (depicted by squares) shows an increase in current that is proportional to the uric acid concentration. However, the corrected current (depicted by triangles) which is processed by Equation 7a shows no effect from the increasing uric acid concentration.
  • [0069]
    FIG. 12 shows the current responses of the first working electrode tested with 240 mg/dL glucose samples in blood spiked with varying levels of uric acid. The purpose of testing strips at 240 mg/dL glucose is to show that the correction algorithm of Equation 7a is also valid over a range of glucose concentrations. Similar to FIG. 11, the uncorrected current at the first working electrode (depicted by squares) shows an increase in current that is proportional to the uric acid concentration. However, the corrected current (depicted by triangles) shows no effect from the increasing uric acid concentration.
  • EXAMPLE 2
  • [0070]
    To show that the method of correcting the current for interferents applies to a wide variety of interferents, strips built according to the embodiment of FIG. 1 were also tested with acetaminophen and gentisic acid at various concentration levels, in addition to uric acid. For purposes of quantitating the magnitude of this effect, a change in glucose output of greater than 10% (for glucose level>70 mg/dL) or 7 mg/dL (for glucose level<=70 mg/dL) was defined as a significant interference. Table 1 shows that the uncorrected current at the first working electrode shows a significant interferent effect at a lower interferent concentration than strips tested with a corrected current response using Equation 7a. This shows that the method of correcting the current output of the first working electrode using Equation 7a is effective in correcting for interferences. Table 1 shows that the current correction in Equation 7a is effective for interferences with respect to acetaminophen, gentisic acid, and uric acid. Table 1 also shows the concentration range of the interferent which is normally found in blood. In addition, Table 1 also shows that the current correction in Equation 7a is effective at 240 mg/dL glucose concentration level.
  • [0071]
    FIG. 13 shows an exploded perspective view of a test strip 800 that is designed to lance a user's skin layer so as cause physiological fluid to be expressed and collected into test strip 800 in a seamless manner. Test strip 800 includes a substrate 50, a conductive layer 802, an insulation layer 804, a reagent layer 820, an adhesive layer 830, and a top layer 824. Test strip 800 further includes a distal end 58 and a proximal end 60.
  • [0072]
    In test strip 800, conductive layer 802 is the first layer disposed on substrate 50. Conductive layer 802 includes a second working electrode 806, a first working electrode 808, a reference electrode 810, a second contact 812, a first contact 814, a reference contact 816, a strip detection bar 17, as shown in FIG. 13. The material used for conductive layer 802 and the process for printing conductive layer 802 is the same for both test strip 62 and test strip 800.
  • [0073]
    Insulation layer 804 is the second layer disposed on substrate 50. Insulation layer 16 includes a cutout 18 which may have a rectangular shaped structure. Cutout 18 exposes a portion of second working electrode 806, first working electrode 808, and reference electrode 810 which can be wetted with a liquid. The material used for insulation layer 804 and the process for printing insulation layer 804 is the same for both test strip 62 and test strip 800.
  • [0074]
    Reagent layer 820 is the third layer disposed on substrate 50, first working electrode 808 and reference electrode 810. The material used for reagent layer 820 and the process for printing reagent layer 820 is the same for both test strip 62 and test strip 800.
  • [0075]
    Adhesive layer 830 is the fourth layer disposed on substrate 50. The material used for adhesive layer 830 and the process for printing adhesive layer 830 is the same for both test strip 62 and test strip 800. The purpose of adhesive layer 830 is to secure top layer 824 to test strip 800. In an embodiment of this invention, top layer 824 may be in the form of an integrated lance as shown in FIG. 13. In such an embodiment, top layer 824 may include a lance 826 which is located at distal end 58.
  • [0076]
    Lance 826, which may also be referred to as a penetration member, may be adapted to pierce a user's skin and draw blood into test strip 800 such that second working electrode 806, first working electrode 808, and reference electrode 810 are wetted. Lance 826 includes a lancet base 832 that terminates at distal end 58 of the assembled test strip.. Lance 826 may be made with either an insulating material such as plastic, glass, and silicon, or a conducting material such as stainless steel and gold. Further descriptions of integrated medical devices that use an integrated lance can be found in International Application No. PCT/GB01/05634 and U.S. patent application Ser. No. 10/143,399. In addition, lance 826 can be fabricated, for example, by a progressive die-stamping technique, as disclosed in the aforementioned International Application No. PCT/GB01/05634 and U.S. patent application Ser. No. 10/143,399.
  • [0077]
    FIG. 14 is a simplified schematic showing a meter 900 interfacing with a test strip. In an embodiment of this invention the following test strips may be suitable for use with meter 900 which are test strip 62, test strip 162, test strip 800, test strip 2000, test strip 3000, or test strip 5000. Meter 900 has at least three electrical contacts that form an electrical connection to the second working electrode, the first working electrode, and the reference electrode. In particular second contact (13, 103, or 812) and reference contact (15, 105, or 816) connect to a first voltage source 910; first contact (11, 101, or 814) and the reference contact (15, 105, or 816) connect to a second voltage source 920.
  • [0078]
    When performing a test, first voltage source 910 applies a first potential E1 between the second working electrode and the reference electrode; and second voltage source 920 applies a second potential E2 between the first working electrode and the reference electrode. In one embodiment of this invention, first potential El and second potential E2 may be the same such as for example about +0.4 V. In another embodiment of this invention, first potential E1 and second potential E2 may be different. A sample of blood is applied such that the second working electrode, the first working electrode, and the reference electrode are covered with blood. This allows the second working electrode and the first working electrode to measure a current which is proportional to glucose and/or non-enzyme specific sources. After about 5 seconds from the sample application, meter 900 measures an oxidation current for both the second working electrode and the first working electrode.
    TABLE 1
    Summary of Interference Performance Using
    Uncorrected and Corrected Current Output
    Glucose Inteferent Normal
    Concen- Concentration Concentration
    tration where effect is range
    Mode Interferent (mg/dL) signficant of interferent
    Uncorrected Acetaminophen 70 11 1-2
    Uncorrected Gentisic Acid 70 10 0.05-0.5 
    Uncorrected Uric Acid 70 5 2.6-7.2
    Uncorrected Acetaminophen 240 16 1-2
    Uncorrected Gentisic Acid 240 12 0.05-0.5 
    Uncorrected Uric Acid 240 8 2.6-7.2
    Corrected Acetaminophen 70 120 1-2
    Corrected Gentisic Acid 70 47 0.05-0.5 
    Corrected Uric Acid 70 33 2.6-7.2
    Corrected Acetaminophen 240 59 1-2
    Corrected Gentisic Acid 240 178 0.05-0.5 
    Corrected Uric Acid 240 29 2.6-7.2
  • [0079]
    It will be recognized that equivalent structures may be substituted for the structures illustrated and described herein and that the described embodiment of the invention is not the only structure which may be employed to implement the claimed invention. In addition, it should be understood that every structure described above has a function and such structure can be referred to as a means for performing that function. While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to hose skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.
Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US4431004 *Oct 27, 1981Feb 14, 1984Bessman Samuel PImplantable glucose sensor
US4655880 *Aug 1, 1983Apr 7, 1987Case Western Reserve UniversityApparatus and method for sensing species, substances and substrates using oxidase
US5298146 *Oct 26, 1992Mar 29, 1994Bayer AktiengesellschaftDevice for the simultaneous detection of dissimilar gas components
US5354447 *Dec 11, 1992Oct 11, 1994Kyoto Daiichi Kagaku Co., Ltd.Biosensor and method of quantitative analysis using the same
US5582697 *Apr 20, 1995Dec 10, 1996Matsushita Electric Industrial Co., Ltd.Biosensor, and a method and a device for quantifying a substrate in a sample liquid using the same
US5628890 *Sep 27, 1995May 13, 1997Medisense, Inc.Electrochemical sensor
US5650062 *Sep 12, 1995Jul 22, 1997Matsushita Electric Industrial Co., Ltd.Biosensor, and a method and a device for quantifying a substrate in a sample liquid using the same
US5653918 *Jan 11, 1996Aug 5, 1997E. I. Du Pont De Nemours And CompanyFlexible thick film conductor composition
US5708247 *Feb 14, 1996Jan 13, 1998Selfcare, Inc.Disposable glucose test strips, and methods and compositions for making same
US5830343 *Mar 11, 1996Nov 3, 1998Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V.Electrochemical analysis process
US5985116 *Dec 12, 1997Nov 16, 1999Matsushita Electric Industrial Co., Ltd.Biosensor
US6046051 *Jun 27, 1997Apr 4, 2000Hemosense, Inc.Method and device for measuring blood coagulation or lysis by viscosity changes
US6212417 *Aug 20, 1999Apr 3, 2001Matsushita Electric Industrial Co., Ltd.Biosensor
US6258229 *Jun 2, 1999Jul 10, 2001Handani WinartaDisposable sub-microliter volume sensor and method of making
US6287451 *Jun 2, 1999Sep 11, 2001Handani WinartaDisposable sensor and method of making
US6340428 *Mar 31, 1999Jan 22, 2002Matsushita Electric Industrial Co., Inc.Device and method for determining the concentration of a substrate
US6540891 *May 6, 1999Apr 1, 2003Abbott LaboratoriesTest strip
US6599406 *Jul 15, 1998Jul 29, 2003Kyoto Daiichi Kagaku Co., Ltd.Concentration measuring apparatus, test strip for the concentration measuring apparatus, biosensor system and method for forming terminal on the test strip
US6730200 *Apr 28, 2000May 4, 2004Abbott LaboratoriesElectrochemical sensor for analysis of liquid samples
US6790327 *Dec 21, 2001Sep 14, 2004Matsushita Electric Industrial Co., Ltd.Device and method for determining the concentration of a substrate
US6881322 *Jan 25, 2001Apr 19, 2005Matsushita Electric Industrial Co., Ltd.Measuring device using biosensor and biosenor used for it, and dedicated standard liquid
US20020092612 *Feb 22, 2002Jul 18, 2002Davies Oliver William HardwickeRapid response glucose sensor
US20020157947 *Dec 7, 2001Oct 31, 2002Craig RappinElectrochemical sensor and method thereof
US20020168290 *May 9, 2002Nov 14, 2002Yuzhakov Vadim V.Physiological sample collection devices and methods of using the same
US20030143113 *May 9, 2002Jul 31, 2003Lifescan, Inc.Physiological sample collection devices and methods of using the same
US20040120848 *Dec 20, 2002Jun 24, 2004Maria TeodorczykMethod for manufacturing a sterilized and calibrated biosensor-based medical device
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7618522Oct 29, 2004Nov 17, 2009Lifescan Scotland LimitedMethod of reducing interferences in an electrochemical sensor using two different applied potentials
US7648468Dec 31, 2002Jan 19, 2010Pelikon Technologies, Inc.Method and apparatus for penetrating tissue
US7653492 *Oct 29, 2004Jan 26, 2010Lifescan Scotland LimitedMethod of reducing the effect of direct interference current in an electrochemical test strip
US7655119Oct 29, 2004Feb 2, 2010Lifescan Scotland LimitedMeter for use in an improved method of reducing interferences in an electrochemical sensor using two different applied potentials
US7666149Oct 28, 2002Feb 23, 2010Peliken Technologies, Inc.Cassette of lancet cartridges for sampling blood
US7674232Mar 9, 2010Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7682318Jun 12, 2002Mar 23, 2010Pelikan Technologies, Inc.Blood sampling apparatus and method
US7699791Jun 12, 2002Apr 20, 2010Pelikan Technologies, Inc.Method and apparatus for improving success rate of blood yield from a fingerstick
US7713214Dec 18, 2002May 11, 2010Pelikan Technologies, Inc.Method and apparatus for a multi-use body fluid sampling device with optical analyte sensing
US7717863Dec 31, 2002May 18, 2010Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7731729Feb 13, 2007Jun 8, 2010Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7766831Aug 3, 2010Roche Diagnostics International AgSystem, tools, devices and a program for diabetes care
US7822454Oct 26, 2010Pelikan Technologies, Inc.Fluid sampling device with improved analyte detecting member configuration
US7833171Nov 16, 2010Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7841992Dec 22, 2005Nov 30, 2010Pelikan Technologies, Inc.Tissue penetration device
US7850621Jun 7, 2004Dec 14, 2010Pelikan Technologies, Inc.Method and apparatus for body fluid sampling and analyte sensing
US7850622Dec 22, 2005Dec 14, 2010Pelikan Technologies, Inc.Tissue penetration device
US7862520Jun 20, 2008Jan 4, 2011Pelikan Technologies, Inc.Body fluid sampling module with a continuous compression tissue interface surface
US7874994Oct 16, 2006Jan 25, 2011Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7892183Feb 22, 2011Pelikan Technologies, Inc.Method and apparatus for body fluid sampling and analyte sensing
US7901362Dec 31, 2002Mar 8, 2011Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7909774Mar 22, 2011Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7909775Mar 22, 2011Pelikan Technologies, Inc.Method and apparatus for lancet launching device integrated onto a blood-sampling cartridge
US7909777Sep 29, 2006Mar 22, 2011Pelikan Technologies, IncMethod and apparatus for penetrating tissue
US7909778Apr 20, 2007Mar 22, 2011Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7914465Feb 8, 2007Mar 29, 2011Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7938787May 10, 2011Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7959582Mar 21, 2007Jun 14, 2011Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US7976476Jul 12, 2011Pelikan Technologies, Inc.Device and method for variable speed lancet
US7981055 *Dec 22, 2005Jul 19, 2011Pelikan Technologies, Inc.Tissue penetration device
US7981056Jun 18, 2007Jul 19, 2011Pelikan Technologies, Inc.Methods and apparatus for lancet actuation
US7988644Aug 2, 2011Pelikan Technologies, Inc.Method and apparatus for a multi-use body fluid sampling device with sterility barrier release
US7988645Aug 2, 2011Pelikan Technologies, Inc.Self optimizing lancing device with adaptation means to temporal variations in cutaneous properties
US8007446Aug 30, 2011Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US8016774Dec 22, 2005Sep 13, 2011Pelikan Technologies, Inc.Tissue penetration device
US8062231Nov 22, 2011Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US8079960Oct 10, 2006Dec 20, 2011Pelikan Technologies, Inc.Methods and apparatus for lancet actuation
US8123700Jun 26, 2007Feb 28, 2012Pelikan Technologies, Inc.Method and apparatus for lancet launching device integrated onto a blood-sampling cartridge
US8162853Apr 24, 2012Pelikan Technologies, Inc.Tissue penetration device
US8197421Jul 16, 2007Jun 12, 2012Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US8197423Dec 14, 2010Jun 12, 2012Pelikan Technologies, Inc.Method and apparatus for penetrating tissue
US8202231Apr 23, 2007Jun 19, 2012Sanofi-Aventis Deutschland GmbhMethod and apparatus for penetrating tissue
US8206317Dec 22, 2005Jun 26, 2012Sanofi-Aventis Deutschland GmbhTissue penetration device
US8206319Jun 26, 2012Sanofi-Aventis Deutschland GmbhTissue penetration device
US8211037Jul 3, 2012Pelikan Technologies, Inc.Tissue penetration device
US8216154Jul 10, 2012Sanofi-Aventis Deutschland GmbhTissue penetration device
US8221334Jul 17, 2012Sanofi-Aventis Deutschland GmbhMethod and apparatus for penetrating tissue
US8251921Jun 10, 2010Aug 28, 2012Sanofi-Aventis Deutschland GmbhMethod and apparatus for body fluid sampling and analyte sensing
US8267870May 30, 2003Sep 18, 2012Sanofi-Aventis Deutschland GmbhMethod and apparatus for body fluid sampling with hybrid actuation
US8282576Sep 29, 2004Oct 9, 2012Sanofi-Aventis Deutschland GmbhMethod and apparatus for an improved sample capture device
US8282577Oct 9, 2012Sanofi-Aventis Deutschland GmbhMethod and apparatus for lancet launching device integrated onto a blood-sampling cartridge
US8296918Aug 23, 2010Oct 30, 2012Sanofi-Aventis Deutschland GmbhMethod of manufacturing a fluid sampling device with improved analyte detecting member configuration
US8333710Dec 18, 2012Sanofi-Aventis Deutschland GmbhTissue penetration device
US8337419Oct 4, 2005Dec 25, 2012Sanofi-Aventis Deutschland GmbhTissue penetration device
US8337420Mar 24, 2006Dec 25, 2012Sanofi-Aventis Deutschland GmbhTissue penetration device
US8343075Dec 23, 2005Jan 1, 2013Sanofi-Aventis Deutschland GmbhTissue penetration device
US8360991Dec 23, 2005Jan 29, 2013Sanofi-Aventis Deutschland GmbhTissue penetration device
US8382682Feb 26, 2013Sanofi-Aventis Deutschland GmbhMethod and apparatus for penetrating tissue
US8382683Feb 26, 2013Sanofi-Aventis Deutschland GmbhTissue penetration device
US8388551May 27, 2008Mar 5, 2013Sanofi-Aventis Deutschland GmbhMethod and apparatus for multi-use body fluid sampling device with sterility barrier release
US8403864May 1, 2006Mar 26, 2013Sanofi-Aventis Deutschland GmbhMethod and apparatus for penetrating tissue
US8414503Apr 9, 2013Sanofi-Aventis Deutschland GmbhMethods and apparatus for lancet actuation
US8430828Jan 26, 2007Apr 30, 2013Sanofi-Aventis Deutschland GmbhMethod and apparatus for a multi-use body fluid sampling device with sterility barrier release
US8435190Jan 19, 2007May 7, 2013Sanofi-Aventis Deutschland GmbhMethod and apparatus for penetrating tissue
US8439872Apr 26, 2010May 14, 2013Sanofi-Aventis Deutschland GmbhApparatus and method for penetration with shaft having a sensor for sensing penetration depth
US8579831Oct 6, 2006Nov 12, 2013Sanofi-Aventis Deutschland GmbhMethod and apparatus for penetrating tissue
US8622930Jul 18, 2011Jan 7, 2014Sanofi-Aventis Deutschland GmbhTissue penetration device
US8641643Apr 27, 2006Feb 4, 2014Sanofi-Aventis Deutschland GmbhSampling module device and method
US8652831Mar 26, 2008Feb 18, 2014Sanofi-Aventis Deutschland GmbhMethod and apparatus for analyte measurement test time
US8668656Dec 31, 2004Mar 11, 2014Sanofi-Aventis Deutschland GmbhMethod and apparatus for improving fluidic flow and sample capture
US8679033Jun 16, 2011Mar 25, 2014Sanofi-Aventis Deutschland GmbhTissue penetration device
US8690796Sep 29, 2006Apr 8, 2014Sanofi-Aventis Deutschland GmbhMethod and apparatus for penetrating tissue
US8702624Jan 29, 2010Apr 22, 2014Sanofi-Aventis Deutschland GmbhAnalyte measurement device with a single shot actuator
US8702960 *Oct 4, 2011Apr 22, 2014Bionime CorporationMethod for operating a measurement for a sample on an electrochemical test strip
US8721671Jul 6, 2005May 13, 2014Sanofi-Aventis Deutschland GmbhElectric lancet actuator
US8828203May 20, 2005Sep 9, 2014Sanofi-Aventis Deutschland GmbhPrintable hydrogels for biosensors
US8845550Dec 3, 2012Sep 30, 2014Sanofi-Aventis Deutschland GmbhTissue penetration device
US8877023 *Jun 21, 2012Nov 4, 2014Lifescan Scotland LimitedElectrochemical-based analytical test strip with intersecting sample-receiving chambers
US8894832Mar 30, 2011Nov 25, 2014Jabil Circuit (Singapore) Pte, Ltd.Sampling plate
US8905945Mar 29, 2012Dec 9, 2014Dominique M. FreemanMethod and apparatus for penetrating tissue
US8945910Jun 19, 2012Feb 3, 2015Sanofi-Aventis Deutschland GmbhMethod and apparatus for an improved sample capture device
US8965476Apr 18, 2011Feb 24, 2015Sanofi-Aventis Deutschland GmbhTissue penetration device
US9011658Mar 30, 2011Apr 21, 2015Jabil Circuit (Singapore) Pte, Ltd.Sampling plate
US9034639Jun 26, 2012May 19, 2015Sanofi-Aventis Deutschland GmbhMethod and apparatus using optical techniques to measure analyte levels
US9072842Jul 31, 2013Jul 7, 2015Sanofi-Aventis Deutschland GmbhMethod and apparatus for penetrating tissue
US9089294Jan 16, 2014Jul 28, 2015Sanofi-Aventis Deutschland GmbhAnalyte measurement device with a single shot actuator
US9089678May 21, 2012Jul 28, 2015Sanofi-Aventis Deutschland GmbhMethod and apparatus for penetrating tissue
US9144401Dec 12, 2005Sep 29, 2015Sanofi-Aventis Deutschland GmbhLow pain penetrating member
US9186468Jan 14, 2014Nov 17, 2015Sanofi-Aventis Deutschland GmbhMethod and apparatus for penetrating tissue
US9226699Nov 9, 2010Jan 5, 2016Sanofi-Aventis Deutschland GmbhBody fluid sampling module with a continuous compression tissue interface surface
US9248267Jul 18, 2013Feb 2, 2016Sanofi-Aventis Deustchland GmbhTissue penetration device
US9261476Apr 1, 2014Feb 16, 2016Sanofi SaPrintable hydrogel for biosensors
US9314194Jan 11, 2007Apr 19, 2016Sanofi-Aventis Deutschland GmbhTissue penetration device
US9351680Oct 14, 2004May 31, 2016Sanofi-Aventis Deutschland GmbhMethod and apparatus for a variable user interface
US20050109618 *Oct 29, 2004May 26, 2005Davies Oliver W.H.Meter for use in an improved method of reducing interferences in an electrochemical sensor using two different applied potentials
US20050183965 *Oct 29, 2004Aug 25, 2005Davies Oliver William H.Method of reducing interferences in an electrochemical sensor using two different applied potentials
US20070276621 *Oct 29, 2004Nov 29, 2007Davies Oliver William HMethod of Reducing the Effect of Direct Interference Current in an Electrochemical Test Strip
US20080242963 *Mar 7, 2008Oct 2, 2008Disetronic Licensing AgSystem, tools, devices and a program for diabetes care
US20090277565 *Dec 21, 2006Nov 12, 2009Edelbrock Andrew JProcess for Making Electrodes for Test Sensors
US20100018878 *Jan 28, 2010Lifescan Scotland Ltd.Method of reducing interferences in an electrochemical sensor using two different applied potentials
US20100235316 *Sep 16, 2010Matthias EssenpreisSystem, tools, devices and a program for diabetes care
US20100327886 *Mar 27, 2009Dec 30, 2010Toshifumi NakamuraMeasurement device, measurement system, and concentration measurement method
US20130008802 *Jan 10, 2013Bionime CorporationMethod for operating a measurement for a sample on an electrochemical test strip
US20130341208 *Jun 21, 2012Dec 26, 2013Lifescan Scotland LimitedElectrochemical-based analytical test strip with intersecting sample-receiving chambers
US20150176049 *Dec 23, 2013Jun 25, 2015Cilag Gmbh InternationalDetermining usability of analytical test strip
EP2260757A1 *Sep 8, 2006Dec 15, 2010F.Hoffmann-La Roche AgA system, tools, devices and a program for diabetes care
WO2007028271A3 *Sep 8, 2006Jun 7, 2007Hoffmann La RocheA system, tools, devices and a program for diabetes care
WO2007075936A2 *Dec 21, 2006Jul 5, 2007Bayer Healthcare LlcProcess of making electrodes for test sensors
WO2007075936A3 *Dec 21, 2006Aug 23, 2007Bayer Healthcare LlcProcess of making electrodes for test sensors
Classifications
U.S. Classification702/104
International ClassificationG01N27/26, G01N27/403, G01N27/49, A61B5/145, C12Q1/00, G06F19/00, G01N33/487, A61B5/00, G01N27/416
Cooperative ClassificationA61B5/150503, A61B5/150282, A61B5/150435, A61B5/150358, A61B5/150022, G01N27/3274, C12Q1/006, C12Q1/001, A61B5/1486, A61B5/1411, A61B5/14532
European ClassificationA61B5/1486, G01N27/327B, A61B5/145G, C12Q1/00B6B, C12Q1/00B
Legal Events
DateCodeEventDescription
Jan 21, 2005ASAssignment
Owner name: LIFESCAN, SCOTLAND, LTD., UNITED KINGDOM
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:DAVIES, OLIVER WILLIAM HARDWICKE;MARSHALL, ROBERT;BASKEYFIELD, DAMIAN EDWARD HAYDON;AND OTHERS;REEL/FRAME:015615/0231;SIGNING DATES FROM 20041112 TO 20041117