KR20130098381A - Systems and methods for improved stability of electrochemical sensors - Google Patents

Abstract

Provided herein are methods for determining the concentration of an analyte in a sample, and devices and systems used in this regard. In one exemplary embodiment of a method for determining the concentration of an analyte in a sample, a sample comprising the analyte is provided to a sample analysis device having a working electrode and a counter electrode. A potential is applied between the electrodes and a measurement of the parameter correlating to a change in the physical properties of the sample analysis device is calculated. The concentration of the analyte can then be determined in terms of parameters that correlate with changes in physical properties. Systems and devices are also provided that take advantage of parameters that correlate changes in physical properties to make analyte concentration determinations.

Description

SYSTEM AND METHOD FOR IMPROVED STABILITY OF ELECTROCHEMICAL SENSORS

The systems and methods provided herein relate to the field of medical testing, in particular the detection of the presence and / or concentration of an analyte (s) in a sample (eg, a physiological fluid comprising blood).

Determination of analyte concentrations in physiological fluids (e.g., blood-inducing agents such as blood or plasma) is of increasing importance in the present society. This analysis finds use in a variety of applications and settings, including clinical laboratory testing, home testing, and the like, where the results of these tests play a significant role in the diagnosis and management of various disease conditions. The analyte of interest includes glucose for diabetes management, cholesterol for monitoring cardiovascular conditions, and the like.

Conventional methods for analyzing analyte concentration determinations are based on electrochemistry. In this method, an aqueous liquid sample is placed in a sensor, for example a sample reaction chamber in an electrochemical cell consisting of at least two electrodes, ie a working electrode and a counter electrode, wherein the electrodes are subjected to amperometric or total amount of these electrodes. It has an impedance that makes it suitable for coulometric measurements. The component to be analyzed is allowed to react with the reactant to form an oxidizable (or reducible) substance in an amount proportional to the analyte concentration. The amount of oxidizable (or reducible) material present is then electrochemically estimated and related to the analyte concentration in the sample.

A desirable property of all sensor elements is that they have a long shelf life, that is, the sensing characteristics of the sensor elements do not change significantly between manufacture and use (ie, during storage). However, when stored for long periods of time and / or under non-optimal storage conditions, such as high temperatures, high humidity, etc., the sensor's performance may deteriorate. For example, the accuracy of analyte concentration determinations using such sensors can be reduced. It is an object of the present invention to overcome or ameliorate these and other disadvantages of the prior art.

Provided herein are various aspects of systems and methods for determining the concentration of an analyte in a sample. In one such aspect, the systems and methods include using an electrochemical cell to which a potential is applied and the current is measured. Parameters that correlate to the physical properties of the electrochemical cell may also be specified. Based on the parameters correlated to current measurements and physical properties, the methods and systems allow analyte concentrations to be found in a rapid manner while minimizing the effect of the physical properties of the electrochemical cell.

In various embodiments described below, electrochemical cells can be used in various sample analysis devices, such as glucose sensors or immune sensors. The sample analyzed may comprise blood. In one embodiment, the blood may comprise whole blood. The analyte to be analyzed for concentration may include glucose. Analysis of glucose concentration may include oxidation of glucose to glucose acid. In an embodiment, the enzyme GDH with the flavin adenine dinucleotide (FAD) cofactor can be used to catalyze the conversion of glucose to glucose acid. In embodiments where the sample analysis device is an immune sensor, the analyte to be analyzed for concentration may comprise a C-reactive protein.

In one aspect, a method for determining the concentration of an analyte in a sample is disclosed. The method includes introducing a sample into an electrochemical cell of the sample analysis device to cause conversion of the analyte. For example, various electrochemical cells can be used, including cells with spaced apart first and second electrodes and reagents. Once the sample is introduced, the method includes determining a measurement of a parameter that correlates to a physical characteristic of the electrochemical cell, and calculating a correction factor, wherein the correction factor is at least a parameter that correlates to the physical characteristic of the electrochemical cell. It is a point of view. The method then includes determining the concentration of the analyte in terms of correction factors.

In another aspect, an electrochemical system is disclosed. The electrochemical system can include an electrochemical cell having a first electrode and a second electrode, and an instrument connected to the electrochemical cell. The instrument may include a control unit connected to the electrochemical cell to apply a potential between the first electrode and the second electrode of the electrochemical cell, the control unit determining a measurement of a parameter that correlates to the physical characteristics of the electrochemical cell. And use the measurement to calculate the corrected concentration of the analyte in the sample.

In some embodiments, the physical properties with which the correction factors are correlated may be related to at least one of the lifetime of the electrochemical cell and the storage conditions of the electrochemical cell. For example, the storage conditions may include storage temperature and storage time. In one aspect, the parameter that correlates to the physical properties of the electrochemical cell can include the measured capacitance of the electrochemical cell.

In another aspect, a method for measuring the concentration of a calibrated analyte is provided. The method includes applying a sample to a test strip. Once the sample is applied, the method includes applying a first test voltage to the sample for a first time interval between the first and second electrodes sufficient to oxidize the reduced medium at the second electrode. After application of the first test voltage, the method includes applying a second test voltage to the sample for a second time interval between the first electrode and the second electrode sufficient to oxidize the reduced medium at the first electrode. The first glucose concentration may be calculated based on the test current value during the first time interval and the second time interval.

The method can also include determining a capacitance of the test strip and calculating a capacitance corrected glucose concentration based on the first glucose concentration and the capacitance. For example, calculating the capacitance corrected glucose concentration may include calculating a correction factor based on the capacitance and the first glucose concentration, wherein the capacitance corrected glucose concentration is based on the first glucose concentration and the correction factor. Is calculated. For example, the correction factor may be about zero when the capacitance is equal to a predetermined anomalous capacitance of the test strip. In some embodiments, calculating the capacitance corrected glucose concentration comprises dividing the correction factor by 100 and adding 1 to provide an intermediate term and multiplying the intermediate term by the first glucose concentration to provide a capacitance corrected glucose concentration. It may further include.

In some embodiments, the capacitance corrected glucose concentration may be calculated when the capacitance is less than the first capacitance threshold and the first glucose concentration is greater than the first glucose concentration threshold. In some embodiments, the method may also include determining if the correction factor is greater than the correction factor threshold, and then setting the correction factor to the correction factor threshold.

In another aspect, an electrochemical system is disclosed. The electrochemical system can include test strips and test instruments. The test strip may include an electrical contact for mating with the electrochemical cell and the test instrument. The electrochemical cell may comprise a first electrode and a second electrode and a reagent in a spaced apart relationship. The test instrument may include a processor adapted to receive current data from the test strip and further adapted to determine capacitance corrected glucose concentration based on the calculated glucose concentration and the measured capacitance. For example, the measured capacitance can be correlated with the physical properties of the test strip regarding at least one of the life of the test strip and the storage conditions of the test strip. Storage conditions may include, for example, storage temperature and storage time.

In one exemplary embodiment, the test instrument can include a data storage device that includes a glucose concentration threshold and a capacitance threshold. In some embodiments, for example, the processor may determine the capacitance corrected glucose concentration when the measured capacitance is less than the capacitance threshold and the calculated glucose concentration is greater than the glucose concentration threshold.

In the various systems and methods described above, an exemplary method of determining the capacitance of an electrochemical cell can include applying a first test voltage between a first electrode and a second electrode. The first test voltage has an AC voltage component and a DC voltage component, and the AC voltage component may be applied at a predetermined time after application of the first test voltage. The test voltage may also have a DC voltage component with a magnitude sufficient to generate a limiting test current at the second electrode, the second electrode having no reagent layer coating. The method may also include processing a portion of the test current resulting from the AC voltage component into a capacitance value of the electrochemical cell.

These and other embodiments, features, and advantages will become apparent to those skilled in the art when taken with reference to the following more detailed description of various exemplary embodiments of the present invention, together with the accompanying drawings briefly described first.

Various features of the invention are described in detail in the appended claims. A better understanding of this feature can be obtained with reference to the following detailed description and accompanying drawings that illustrate exemplary non-limiting embodiments.

1A is a perspective view of an exemplary test strip.
1B is an exploded perspective view of the test strip of FIG. 1A.
1C is a perspective view of the distal portion of the test strip of FIG. 1A.
FIG. 2 is a bottom plan view of the test strip of FIG. 1A; FIG.
3 is a side plan view of the test strip of FIG. 1A;
4A is a top plan view of the test strip of FIG. 1A.
4B is a partial side view of the distal portion of the test strip according to arrows 4B-4B in FIG. 4A.
5 is a schematic diagram illustrating a test instrument in electrical interface with a test strip contact pad.
6 is an exploded view of an exemplary embodiment of an immune sensor in accordance with the present invention.
FIG. 7A shows a test voltage waveform at which the test instrument applies a plurality of test voltages during a specified time interval. FIG.
FIG. 7B illustrates the transient test current generated with the test voltage waveform of FIG. 6.
8A shows a test voltage waveform when the test instrument applies a plurality of test voltages at opposite polarities for a specified time interval when compared to FIG. 7A.
FIG. 8B shows the transient test current generated with the test voltage of FIG. 8A.
9 is a chart showing the relationship between capacitance and bias percentage for multiple tests.

The following detailed description should be read with reference to the drawings, wherein like elements in different drawings are designated by the same reference numerals. The drawings, which are not necessarily drawn to scale, illustrate selected embodiments and are not intended to limit the scope of the invention. The detailed description illustrates the principles of the invention by way of example, and not limitation.

As used herein, for any numerical value or range, the term "about" or "approximately" refers to suitable dimensional tolerances that enable a portion or set of components to function for their intended purpose as described herein. To indicate. In addition, as used herein, the terms “patient”, “host”, “user” and “subject” refer to any human or animal subject and are not intended to limit the system or method to human use, but a human patient. The use of the invention in represents a preferred embodiment.

Particular example embodiments will now be described to provide a thorough understanding of the principles of the structure, function, manufacture, and use and methods of the systems disclosed herein. One or more examples of these embodiments are shown in the accompanying drawings. Those skilled in the art will understand that the systems and methods specifically described herein and shown in the accompanying drawings are non-limiting exemplary embodiments, and the scope of the present invention is defined only by the claims. Features shown or described in connection with one exemplary embodiment can be combined with features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.

The systems and methods disclosed herein are suitable for use in the determination of a wide range of analytes in a wide range of samples, and particularly for use in the determination of analytes in whole blood, plasma, serum, interstitial fluids or derivatives thereof. In an exemplary embodiment, a glucose test system based on thin cell design with opposing electrodes and fast (e.g., about 5 seconds analysis time) tri-pulse electrochemical detection is a small sample (e.g., about 0.4 μL). ), And can provide improved reliability and accuracy of blood glucose measurement. In the reaction cell for analyzing the analyte, the glucose in the sample can be oxidized to gluconolactone using glucose dehydrogenase and an electrochemically active medium can be used to transport electrons from the enzyme to the palladium working electrode. More specifically, the reagent layer coating at least one of the electrodes in the reaction cell may comprise glucose dehydrogenase (GDH) based on pyroquinoline quinone (PQQ) cofactor and ferricyanide. In another embodiment, the enzyme GDH based on the PQQ cofactor may be replaced with the enzyme GDH based on the flavin adenine dinucleotide (FAD) cofactor. When blood or control solution is administered into the reaction chamber, glucose is oxidized by GDH (ox) and GDH (ox) to GDH (red) in the process, as shown below in chemical conversion T.1. To convert. GDH (ox) refers to the oxidation state of GDH, and GDH (red) refers to the reduced state of GDH.

T.1 D-glucose + GDH (ox) → Glucose + GDH (red)

Potentiostats can be used to apply tri-pulse potential waveforms to the working and counter electrodes, creating a transient test current used to calculate glucose concentration. In addition, additional information obtained from transient test currents can be used to distinguish between sample matrices, correct variability in blood samples based on erythrocyte volume fraction, temperature variations, electrochemically active components, and identify possible system errors.

The method of the invention can in principle be used with any type of electrochemical cell having spaced apart first and second electrodes and reagent layers. For example, the electrochemical cell can be in the form of a test strip. In one aspect, the test strip may include two opposing electrodes separated by thin spacers to define the sample receiving chamber or zone in which the reagent layer is located. Applicants note that other types of test strips, including, for example, test streams with coplanar electrodes, may also be used with the methods described herein.

Electrochemical cell

1A-4B show various views of an exemplary test strip 62 suitable for use with the methods described herein. As shown, the test strip 62 may include an elongated body that extends from the proximal end 80 to the distal end 82 and has lateral edges 56, 58. The proximal portion of the body 59 may include a sample reaction chamber 61 and reagents 72 having multiple electrodes 164, 166, and the distal portion of the test strip body 59 is in electrical communication with the test instrument. It may include configured features. In use, the physiological fluid or control solution may be delivered to the sample reaction chamber 61 for electrochemical analysis.

In an exemplary embodiment, the test strip 62 may include a first electrode layer 66 and a second electrode layer 64 with a spacer layer 60 positioned therebetween. The first electrode layer 66 can provide a first electrode 166 and a first connection track 76 for electrically connecting the first electrode 166 to the first electrical contact 67. Similarly, the second electrode layer 64 can provide a second connecting track 78 for electrically connecting the second electrode 164 and the second electrode 164 with the second electrical contact 63. .

In one embodiment, the sample reaction chamber 61 is formed by the first electrode 166, the second electrode 164, and the spacer 60, as shown in FIGS. 1A-4B. In detail, the first electrode 166 and the second electrode 164 form the bottom and the top of the sample reaction chamber 61, respectively. The cutout region 68 of the spacer 60 may form a sidewall of the sample reaction chamber 61. In one aspect, the sample reaction chamber 61 may further include a plurality of ports 70 providing sample inlets and / or vents. For example, one of the ports can provide fluid sample entry and the other port can act as a vent.

The sample reaction chamber 61 may have a small volume. For example, the volume may range from about 0.1 microliters to about 5 microliters, preferably about 0.2 microliters to about 3 microliters, more preferably about 0.3 microliters to about 1 microliter. As will be appreciated by those skilled in the art, the sample reaction chamber 61 may have a variety of other such volumes. To provide a small sample volume, the cutout 68 is about 0.01 cm ² to about 0.2 cm ² , preferably about 0.02 cm ² to about 0.15 cm ² , more preferably about 0.03 cm ² to about 0.08 cm ² It may have an area in the range of. Similarly, those skilled in the art will understand that volume cutout 68 may have a variety of other such areas. In addition, the first and second electrodes 166, 164 range from about 1 micron to about 500 microns, preferably from about 10 microns to about 400 microns, more preferably from about 40 microns to about 200 microns Can be spaced apart. In other embodiments, this range may vary between various other values. The close spacing of the electrodes also allows for redox cycling to occur, where the oxidized media produced at the first electrode 166 can diffuse to the second electrode 164 and be reduced, after which the first electrode ( 166) to be oxidized again.

At the distal end of the test strip body 59, a first electrical contact 67 can be used to establish an electrical connection to the test instrument. The second electrical contact 63 can be accessed by the test instrument via the U-shaped notch 65 as shown in FIG. 2. Applicants note that test strip 62 may include various alternative electrical contacts configured for electrically connecting to a test instrument. For example, US Pat. No. 6,379,513, which is incorporated by reference in its entirety, discloses electrochemical cell connection means.

In one embodiment, first electrode layer 66 and / or second electrode layer 64 may comprise gold, palladium, carbon, silver, platinum, tin oxide, iridium, indium, and combinations thereof (eg, indium doped oxide). Conductive material formed from a material such as tin). In addition, the electrode can be formed by depositing a conductive material on an insulating sheet (not shown) by various processes such as, for example, sputtering, electroless plating or screen printing processes. In one exemplary embodiment, the second electrode layer 64 may be a sputtered gold electrode and the first electrode layer 66 may be a sputtered palladium electrode. Suitable materials that can be used as the spacer layer 60 are, for example, various such as plastics (eg, PET, PETG, polyimide, polycarbonate, polystyrene), silicone, ceramics, glass, adhesives, and combinations thereof. Insulation material.

Reagent layer 72 may be disposed within sample reagent chamber 61 using processes such as slot coating, dispensing from the end of the tube, inkjetting, and screen printing. Such a process is described, for example, in US Pat. Nos. 6,749,887, 6,869,411, 6,676,995 and 6,830,934, each of which is incorporated herein by reference in its entirety. In one embodiment, reagent layer 72 may include at least a mediator and an enzyme and may be deposited on first electrode 166. Various mediators and / or enzymes are within the spirit and scope of the present invention. For example, suitable mediators include ferricyanide, ferrocene, ferrocene derivatives, osmium bipyridyl complexes and quinone derivatives. Examples of suitable enzymes are Glucose Dehydrogenase (GDH) based on Glucose Oxidase, Pyroquinoline Quinone (PQQ) Cofactor, GDH based on Nicotinamide Adinedine Dinucleotide Cofactor, and GDH based on FAD [EC1.1.99.10] It includes. One exemplary reagent formulation that may be suitable for preparing the reagent layer 72 is disclosed herein as US Patent Application Publication No. 2004/0120848, the entirety of which is incorporated herein by reference. And in pending US patent application Ser. No. 10 / 242,951, entitled "Method of Manufacturing a Sterilized and Calibrated Biosensor-Based Medical Device."

The first electrode 166 or the second electrode 164 can function as a working electrode that oxidizes or reduces a limited amount of media depending on the polarity of the applied test potential of the test instrument. For example, if the current limiting species is a reduced medium, it can be oxidized at the first electrode 166 as long as sufficient positive potential is applied to the second electrode 164. In this situation, the first electrode 166 performs the function of the working electrode, and the second electrode 164 performs the function of the counter / reference electrode. It should be noted that unless otherwise noted for the test strip 62, all potentials applied by the test instrument 100 will be referred to below for the second electrode 164.

Similarly, if a sufficient negative potential is applied to the second electrode 164, the reduced medium can be oxidized at the second electrode 164. In this situation, the second electrode 164 may perform the function of the working electrode, and the first electrode 166 may perform the function of the counter / reference electrode.

Initially, the method disclosed herein may include introducing a predetermined amount of fluid sample of interest into a test strip 62 comprising a first electrode 166, a second electrode 164, and a reagent layer 72. Can be. The fluid sample may be whole blood or derivatives or fractions or control solutions thereof. Fluid samples, such as blood, may be administered into the sample reaction chamber 61 via the port 70. In one aspect, the port 70 and / or sample reaction chamber 61 may be configured such that capillary action enables the fluid sample to fill the sample reaction chamber 61.

5 illustrates a test instrument 100 that interfaces with a first electrical contact 67 and a second electrical contact 63 in electrical communication with a first electrode 166 and a second electrode 164 of a test strip 62, respectively. Provides a simplified schematic. The test instrument 100 may be configured to electrically connect to the first electrode 166 and the second electrode 164 via each of the first electrical contact 67 and the second electrical contact 63 (FIG. 2). And as shown in FIG. 5). As will be appreciated by those skilled in the art, various test instruments can be used with the methods described herein. However, in one embodiment, the test instrument includes at least one processor that performs calculations that are capable of calculating correction factors in terms of at least one measured parameter that correlates to the physical properties of the electrochemical cell. And one or more control units configured for data classification and / or storage as well. The microprocessor may be in the form of a mixed signal microprocessor (MSP), such as, for example, Texas Instruments MSP 430. The TI-MSP 430 can also be configured to perform some of the potentiometer and current measurement functions. In addition, the MSP 430 may also include volatile and nonvolatile memory. In other embodiments, multiple electronic components may be integrated with microcontrollers in the form of application specific integrated circuits.

As shown in FIG. 5, electrical contact 67 may include two prongs 67a, 67b. In one exemplary embodiment, the test instrument 100 is individually connected to the rakes 67a and 67b to complete the circuit when the test instrument 100 interfaces with the test strip 62. The test instrument 100 can measure the resistance or electrical continuity between the rakes 67a and 67b to determine whether the test strip 62 is electrically connected to the test instrument 100. Applicants note that the test instrument 100 can use various sensors and circuits to determine when the test strip 62 is properly positioned relative to the test instrument 100.

In one embodiment, a circuit disposed within the test instrument 100 may apply a test potential and / or a current between the first electrical contact 67 and the second electrical contact 63. Once the test instrument 100 recognizes that the strip 62 is inserted, the test instrument 100 is turned on and enters the fluid detection mode. In one embodiment, the fluid detection mode enables the test instrument 100 to apply a constant microcurrent of one microampere between the first electrode 166 and the second electrode 164. Since the test strip 62 is initially dry, the test meter 100 measures the maximum voltage that is limited by the hardware in the test meter 100. However, once the user dispenses a fluid sample on the inlet 70, this causes the sample reaction chamber 61 to fill. When the fluid sample bridges into the gap between the first electrode 166 and the second electrode 164, the test instrument 100 measures a measurement voltage that is below a predetermined threshold that causes the test instrument 100 to automatically initiate a glucose test. Will be measured (eg, as described in US Pat. No. 6,193,873, which is incorporated herein by reference in its entirety).

It should be noted that the measured voltage can be reduced below a predetermined threshold when only a portion of the sample reaction chamber 61 is charged. The method of automatically recognizing that the fluid is applied does not necessarily indicate that the sample reaction chamber 61 is fully filled, but can only confirm the presence of a predetermined amount of fluid in the sample reaction chamber 61. Once the test instrument 100 determines that fluid is applied to the test strip 62, a short but nonzero time may still be required to fully fill the sample reaction chamber 61 with the fluid.

Another exemplary embodiment of a sample analysis device for use with at least some of the methods disclosed herein, namely the immune sensor 110, is shown in FIG. 6, the content of which is incorporated herein by reference as such. US patent application Ser. No. 12 / 570,268 to Chatelier et al., Entitled "Adhesive Compositions for Use in an Immunosensor," filed September 30, have. A plurality of chambers may be formed in the immune sensor, including a fill chamber that allows the sample to react with one or more desired materials and a detection chamber that allows the concentration of a particular component of the sample to be determined. These chambers may be formed in at least a portion of the separator of the first electrode, the second electrode and the immune sensor. The immune sensor may also include a vent to allow air to enter and exit the immune sensor as desired, and first and second sealing components for selectively sealing the first and second sides of the vent. The first sealing part can also form a wall of the filling chamber.

As shown, the immune sensor 110 includes a first electrode 112 having two liquid reagents 130, 132 stripped thereon. The first electrode 112 can be formed using any number of techniques used to form the electrode, but in one embodiment a polyethylene terephthalate (PET) sheet filled with barium sulfate is sputter coated with gold. PET sheets can also be filled with titanium dioxide. Other non-limiting examples of forming electrodes include Hodges et al., Filed November 10, 2000, the contents of which are incorporated herein by reference in their entirety, as "Electrochemical Cells." US Pat. No. 6,521,110.

블록 공중합체와 같은 폴록사머에 공액결합된 항체, 시트라코네이트와 같은 항응고제 및 칼슘 이온을 포함한다. 일 실시예에서, 제 2 액체 시약(132)은 희석 시트라콘산 용액과 같은 산성 완충제 내의 페리시아나이드, 포도당 및 페나진 에토설페이트와 같은 제 2 매개체의 혼합물을 포함한다. 제 1 및 제 2 액체 시약(130, 132)은 제 1 전극(112) 상에 건조될 수 있다. 다수의 기술이 시약(130, 132)을 건조하는데 사용될 수 있지만, 일 실시예에서 제 1 전극(112) 상의 시약(130, 132)의 스트립핑 후에, 하나 이상의 적외선 건조기가 시약(130, 132)에 적용될 수 있다. 하나 이상의 공기 건조기는 또한 예를 들어 적외선 건조기 이후에 사용될 수 있다. 본 명세서에서 제 1 시약 및 제 1 액체 시약과 제 2 시약 및 제 2 액체 시약의 언급은 상호 교환 가능하게 사용되고, 특정 실시예에 대해 시약이 소정 시간에 이들의 액체 또는 건조 형태에 있는 것을 반드시 지시하는 것은 아니다. 또한, 제 1 및 제 2 액체 시약과 연관된 성분의 일부는 상호 교환 가능하게 사용될 수 있고 그리고/또는 원하는 바와 같이 제 1 및 제 2 액체 시약의 모두에 사용될 수 있다. 비한정적인 예로서, 항응고제는 제 1 액체 시약(130) 및 제 2 액체 시약(132) 중 하나 또는 모두와 연관될 수 있다.Likewise, liquid reagents 130 and 132 may have a number of different compositions. In one embodiment, the first liquid reagent 130 is an enzyme such as GDH-PQQ in a buffer containing sucrose, as well as Pluronics.

Antibodies conjugated to poloxamers such as block copolymers, anticoagulants such as citraconate and calcium ions. In one embodiment, the second liquid reagent 132 comprises a mixture of second mediators such as ferricyanide, glucose and phenazine ethosulfate in an acidic buffer such as dilute citraconic acid solution. The first and second liquid reagents 130 and 132 may be dried on the first electrode 112. Although a number of techniques may be used to dry the reagents 130, 132, in one embodiment after stripping the reagents 130, 132 on the first electrode 112, one or more infrared dryers may be used. Can be applied to One or more air dryers may also be used after the infrared dryer, for example. References herein to the first reagent and the first liquid reagent and the second reagent and the second liquid reagent are used interchangeably and, for certain embodiments, necessarily indicate that the reagents are in their liquid or dry form at a given time. It is not. In addition, some of the components associated with the first and second liquid reagents may be used interchangeably and / or may be used with both the first and second liquid reagents as desired. As a non-limiting example, the anticoagulant may be associated with one or both of the first liquid reagent 130 and the second liquid reagent 132.

Lines may be formed in the sputter coated gold between reagents 130 and 132 such that the edge of reagent 132 is very close to or in contact with the line. The line can be applied using laser ablation or with sharp metal edges. In one exemplary embodiment, the line may be applied before reagents 130 and 132 are stripped onto the electrode. The line may be designed to electrically insulate the section of the first electrode 112 below the detection chamber from the section that may be below the reaction chamber. This may provide better definition of the area of the working electrode during the electrochemical analysis.

The immune sensor 110 may also include a second electrode 114 having one or more magnetic beads 134 containing a surface binding antigen thereon. The antigen may be configured to react with an antibody disposed on the first electrode 112 and a sample in the reaction chamber 118, as described in more detail below. Those skilled in the art will appreciate that components disposed on the first electrode 112 and on the second electrode 114 may be interchangeable. Accordingly, the first electrode 112 can include one or more magnetic beads 134, and the second electrode 114 can include two liquid reagents 130, 132 stripped thereon. Further, while in the illustrated embodiment the length of the electrode 112 forms the length of the entire body of the immune sensor 110, in other embodiments the electrode is merely a layer of a layer of the immune sensor functioning as a first or second electrode. It may be part or multiple electrodes can be disposed on a single layer of the immune sensor. In addition, since the voltage applied to the immune sensor can be flipped and / or alternating, each of the first and second electrodes can function as a working electrode and a counter electrode or counter / reference electrode at different stages. For ease of explanation, in the present application, the first electrode is considered as the working electrode and the second electrode is considered as the counter or counter / reference electrode.

The separator 116 disposed between the first and second electrodes 112 and 114 may have various shapes and sizes, but in general, the first and second electrodes 112 and 114 are preferably combined to provide an immune sensor ( And to form 110). In one exemplary embodiment, separator 116 includes adhesive on both sides. Separator 116 may further include a release liner on each side of the two sides of separator 116. Separator 116 may be cut in a manner to form at least two cavities. The first cavity may be formed to function as the reaction chamber 118, and the second cavity may be formed to function as the detection chamber 120. In one embodiment, the separator 116 allows the reaction chamber 118 to align with the electrodes 112 and 114 to allow antigen-antibody reactions therein, while the detection chamber 120 includes electrodes 112 and 114. And can be kiss-cut to permit electrochemical determination of ferrocyanide therein.

In one embodiment, the separator 116 allows the magnetic beads 134 of the second electrode 114 and the first reagent 130 of the first electrode 112 to be at least partially disposed in the reaction chamber 118. The ferricyanide-glucose combination of the second reagent 132 of the first electrode 112 may be disposed on the first electrode 112 in a manner such that it at least partially is disposed within the detection chamber 120. It may be advantageous to include an anticoagulant in each of the first and second liquid reagents 130, 132 such that the anticoagulant is associated with each reaction chamber 118 and the detection chamber 120. In some embodiments, a combination of one of the first and second electrodes 112, 114 and separator 116 may be stacked together to form a bi-laminate, while in other embodiments each The combination of the first electrode 112, the second electrode 114, and the separator 16 can be stacked together to form a tri-laminate. Alternatively, additional layers may also be added.

The filling chamber 122 may be formed by drilling holes in one of the first and second electrodes 112, 114 and in the separator 116. In the illustrated embodiment, the charging chamber is formed by drilling holes in the first electrode 112 and separator 116 such that the holes in the first electrode 112 overlap the reaction chamber 118. As shown, the charging chamber 122 may be spaced a predetermined distance from the detection chamber 120. This configuration allows the sample to enter the immune sensor 110 through the filling chamber 122, does not enter the detection chamber 120, and flow into the reaction chamber 118 is for example the first electrode 112. And react with first liquid reagent 130 comprising an enzyme conjugated to magnetic beads 134 stripped onto second electrode 114 and an enzyme in a buffer in the bed. Once the sample has been reacted, the sample will flow into the detection chamber 120 to experience chemical or physical conversion in an acidic buffer with a mixture of a second liquid reagent 132, eg, ferricyanide, glucose and a second mediator. Can be.

Ventilation openings 124 may be formed by drilling holes through the two electrodes 112, 114 and separator 116, respectively, to extend through the entirety of the immune sensor 110. The holes may be formed in a suitable manner such as, for example, drilling or drilling at a number of different locations, but in one exemplary embodiment the holes may overlap an area of the detection chamber 120 spaced from the reaction chamber 118. have.

The vent 124 can be sealed in a number of different ways. In the illustrated embodiment, a first sealing component 140 is positioned on the first electrode 112 to seal the first side of the vent 124, and a second sealing component 142 of the vent opening 124. Positioned on the second electrode 114 to seal the second side. The sealing parts can be made and / or comprise any number of materials. As a non-limiting example, one or both of the sealing parts may be hydrophilic adhesive tape or Scotch. It may be a tape. Adhesive surfaces of the sealing components may face the immune sensor 110. As shown, the first sealing component 140 can not only form a seal for the vent 124, but can also form a wall for the filling chamber 122 so that the sample can be included therein. Properties incorporated on the adhesive side of the first sealing component 140 may be associated with the filling chamber 122. For example, if the first sealing component 140 includes a property that makes it hydrophilic and / or water soluble, the filling chamber can be kept well wet when the sample is placed therein. In addition, the sealing components 140, 142 may be selectively coupled to and separated from the immune sensor 110 to provide ventilation and / or sealing of the immune sensor 110 and the components disposed therein as desired.

Adhesives can generally be used in the construction of immune sensors. A non-limiting example where an adhesive can be incorporated into the immune sensor and other sample analysis devices of the present invention is used in the immunological sensor filed September 30, 2009, the content of which is already incorporated herein in its entirety. Adhesive composition for the invention, "US Patent Application No. 12 / 570,268 to Shatlie et al.

Although the present invention describes various different embodiments related to the immune sensor, other embodiments of the immune sensor may also be used with the methods of the present invention. Non-limiting examples of such embodiments are described in US Patent Application Publication No. 2003/0180814, Hossie et al., April 2004, entitled “Direct Immunosensor Assay,” filed March 21, 2002. US Patent Application Publication No. 2004/0203137 by Hodges et al., Entitled “Immunosensor,” and entitled “Biosensor Apparatus”, filed November 21, 2005. and US Patent Application Publication No. 12/0134713 and US Patent Application Publication Nos. 2003/0180814 and 2004/0203137 to Rylatt et al. Including those described in US Pat. No. 563,091, each of which is incorporated herein by reference in its entirety.

In one embodiment, the immune sensor 110 may be configured to be placed in an instrument configured to apply a potential to the electrodes 112, 114 and measure the current resulting from the application of the potential, for example, via a suitable circuit. have. In one embodiment, the immune sensor includes one or more tabs 117 for coupling to the instrument. Other features may also be used to couple the instrument with the immune sensor 110. The instrument may include a number of different features. For example, the meter may include a magnet configured to retain certain components of the immune sensor 110 within one chamber while other components flow into the other chamber. In one exemplary embodiment, the magnet of the meter is positioned such that when placing the immune sensor 110 in the meter, the magnet is placed below the reaction chamber 118. This can help the magnet to prevent any magnetic beads 134 and more specifically any antibody-enzyme conjugates bound to the beads 134 to flow into the detection chamber 120.

An alternative feature of the instrument includes a heating element. The heating element can help accelerate the reaction rate and reduce sample viscosity to aid sample flow through the immune sensor 110 in a desired manner. The heating element allows one or more chambers and / or samples disposed therein to be heated to a predetermined temperature. Heating to a predetermined temperature may help to provide accuracy by, for example, reducing or eliminating the effect of the temperature change when the reaction occurs.

In addition, a penetrating mechanism can also be combined with the instrument. The through mechanism can be configured to penetrate at least one of the first and second sealing components at a desired time such that air can flow out of the vent and liquid can flow from the reaction chamber into the detection chamber.

Immune sensor 110 and test strip 62 may also be configured to be coupled with a control unit. The control unit can be configured to perform various functions. In one exemplary embodiment, the control unit is capable of measuring the charging time of the sample when introduced into the device. In another embodiment, the control unit may be configured to determine the erythrocyte volume fraction value of the blood sample. In another embodiment, the control unit may be configured to calculate the concentration of the analyte in the sample in terms of filling time. Indeed, the control unit may comprise at least in part a number of different features depending on how the system is designed to measure the charging time and the desired functionality.

The control unit may also specify other aspects of the system. As a non-limiting example, the control unit may be configured to measure the temperature of one or more chambers of an immune sensor or test strip. The control unit may also be configured to measure the temperature of the sample, the color of the sample, the capacitance of the immune sensor or test strip, or various other features and / or the properties of the sample and / or system. As another non-limiting example, the control unit may be configured to communicate the result of the charge time determination, the result of the capacitance measurement, the result of the analyte concentration determination, and / or the red blood cell volume ratio measurement to external equipment. This can be accomplished in any number of methods. In one embodiment, the control unit can be wired connected to the microprocessor and / or display device. In another embodiment, the control unit may be configured to wirelessly transmit data from the control unit to the microcontroller and / or display device.

Other parts of the system can also be configured to make these measurements. For example, an immune sensor or instrument measures the temperature of one or more chambers of the immune sensor or test strip, measures or represents the temperature of the sample, measures various other features and / or characteristics of the sample and / or system, and determines Or can be configured to represent. Furthermore, those skilled in the art will recognize that these features of the control unit can be interchanged and optionally combined within a single control unit. For example, the control unit can determine the charging time, capacitance, and measure the temperature of the chamber. In other embodiments, multiple control units may be used together to perform various functions, based at least in part on the desired functions to be performed and the configuration of the various control units.

Analyte  Concentration test

In one embodiment, once the test instrument 100 determines that fluid is introduced (eg, administered) on the test strip 62, the test instrument 100 is configured for a specified interval as shown in FIG. 7A. The glucose test can be performed by applying a plurality of test potentials to the test strip 62. The glucose test time interval (T _G) is a glucose test time interval (T _G) is the first test potential time interval (T ₁₎ a first test potential (E ₁₎ for the second test potential time interval (T ₂₎ The amount of time to perform the glucose test, which may include the third test potential E ₃ for the second test potential E ₂ and the third test potential time interval T ₃ , for Not all calculations are involved in glucose testing). In addition, as shown in FIG. 7A, the second test potential time interval T ₂ may include a constant (DC) test voltage component and an overlapping alternating current (AC) or oscillation test voltage component. Overlapping alternating test voltage components may be applied for the time interval indicated by the T _cap . The glucose test time interval T _G can be in a range from about 1 second to about 5 seconds, for example.

As described above, the first electrode 166 or the second electrode 164 can function as a working electrode that oxidizes or reduces the limiting amount of the medium depending on the polarity of the applied test potential of the test instrument. It should be noted that unless otherwise noted, all potentials applied by the test instrument 100 will be referred to the second electrode 1640 below. However, Applicants note that the test potential applied by the test instrument 100 may also be referenced to the first electrode 166, in which case the polarity and measurement current of the test potential described below may be reversed. Please note.

The plurality of test current values measured during the first, second and third test potential time intervals may be performed at a frequency ranging from about 1 measurement per nanosecond to about 1 measurement per approximately 100 milliseconds. Applicants note that the terms "first," "second," and "third" are selected for convenience and do not necessarily reflect the order in which the test potentials are applied. For example, an embodiment can have a potential waveform to which a third test voltage can be applied before application of the first and second test voltages. While an embodiment using three test voltages in a tandem manner is described, Applicants note that the glucose test may include different numbers of open circuits and test voltages. Applicants note that the glucose test time interval may comprise any number of open circuit potential time intervals. For example, the glucose test time interval may comprise only two test potential time intervals and / or open circuit time intervals before and / or after one or more test potential time intervals. In another exemplary embodiment, the glucose test may include an open circuit for a first time interval, a second test voltage for a second time interval, and a third test voltage for a third time interval.

As shown in FIG. 7A, the test instrument 100 includes a first test potential E ₁ (eg, a first test potential time interval T ₁ ) (eg, in a range from about 0 seconds to about 1 second). For example, as shown in FIG. 7A, about −20 mV) may be applied. The first test potential time interval T ₁ may range from about 0.1 seconds to about 3 seconds from the start of zero seconds in FIG. 7A, preferably from about 0.2 seconds to about 2 seconds, most Preferably from about 0.3 seconds to about 1 second. The first test potential time interval T ₁ may be long enough to allow the sample reaction chamber 61 to be fully filled with the sample and also to allow the reagent layer 72 to be at least partially dissolved or solvated. In other embodiments, the first test potential time interval T ₁ may include any other desired time range.

In one embodiment, the test instrument 100 has a first test potential between the electrodes for a period between when the meter can detect that the strip is filled with a sample and before the second test potential E ₂ is applied. (E ₁ ) may be applied. In one aspect, the test potential E ₁ is small. For example, the potential can range from about −1 to about −100 mV, preferably from about −5 mV to about −50 mV, most preferably from about −10 mV to about −30 mV. . The smaller potential disturbs the reduced mediator concentration gradient to a lesser extent compared to applying a larger potential difference, but is still sufficient to obtain a measure of the oxidizable material in the sample. The test potential E ₁ may be applied for a portion of the time between the detection of the charge and the second test potential E ₂ or for the entirety of this time period. If the test potential E ₁ is used for part of the time, an open circuit can be applied for the remainder of the time. As long as the total duration of application of the small potential E ₁ is sufficient to obtain a current measurement indicating the presence and / or amount of the oxidizable material present in the sample, the order and time of their application is important in this example. Alternatively, any number of combinations of open circuit and small voltage potential application can be applied. In a preferred embodiment, a small potential E ₁ is applied for substantially the entire period when the charge is detected and when the second test potential E ₂ is applied.

During the first time interval T ₁ , the test instrument 100 measures the final first transient current, which may be referred to as i _a (t). The transient current represents a plurality of current values measured by the test instrument during a particular test potential time interval. The first transient current may be an average or multiplied by the single current value measured during the first test potential time interval or the time interval of the first test potential time interval or the integration of the current value over the first test potential time interval. In some embodiments, the first transient current may comprise a current value measured over various time intervals during the first test potential time interval. In one embodiment, the first transient current [i _a (t)] ranges from about 0.05 seconds to about 1.0 seconds, preferably from about 0.1 seconds to about 0.5 seconds, most preferably from about 0.1 seconds to about 0.2 seconds Can be measured for a time. In another embodiment, the first transient current i _a (t) can be measured for another desired time range. As described below, some or all of the first transient can be used in the methods described herein to determine whether a control solution or blood sample has been applied to the test strip 62. The magnitude of the first transient current is affected by the presence of an easily oxidizable material in the sample. Blood generally contains endogenous and exogenous compounds that are readily oxidized at the second electrode 164. Conversely, the control solution can be formulated to contain no oxidizable compounds. However, the blood sample composition can vary, and the magnitude of the first transient current for the high viscosity blood sample can typically be smaller than the low viscosity sample because the sample reaction chamber 61 may not be fully charged after about 0.2 seconds. (In some cases even smaller than the control solution sample). Incomplete charging can cause the effective area of the first electrode 166 and the second electrode 164 to be reduced, which in turn can reduce the first transient current. Thus, the presence of the oxidizable substance in the sample itself is not always a sufficient distinguishing factor due to the variation in the blood sample.

Once the first time interval T ₁ time has elapsed, the test instrument 100 may wait for a second test potential time interval T ₂ (eg, about 3 seconds, as shown in FIG. 7A). A second test potential E ₂ (eg, about −300 mV, as shown in FIG. 7A) may be applied between the first electrode 166 and the second electrode 164. The second test potential E ₂ may be a sufficiently negative value of the mediator redox potential such that a limiting oxidation current occurs at the second electrode 164. For example, when using ferricyanide and / or ferrocyanide as mediators, the second test potential E ₂ may range from about −600 mV to about 0 mV, preferably from about −600 mV to It may range from about -100 mV, more preferably about -300 mV. Likewise, the time interval indicated as t _{cap in} FIG. 6 can also last over a predetermined time range, but in one exemplary embodiment it has a duration of about 20 milliseconds. In one exemplary embodiment, the superimposed alternating test voltage component is applied after about 0.3 seconds to about 0.32 seconds after application of the second test voltage (V ₂ ), with an amplitude of about +/- 50 mV and about 109 Hz. Induce two cycles of a sine wave with frequency. During the second test potential time interval T ₂ , the test instrument 100 can measure the second transient current i _b (t).

The second test potential time interval T ₂ may be long enough to monitor the rate of production of reduced mediator (eg, ferrocyanide) in the sample reaction chamber 61 based on the magnitude of the limiting oxidation current. The reduced mediator may be generated by a series of chemical reactions in the reagent layer (& 2). During the second test potential time interval T ₂ , the limiting amount of the reduced mediator is oxidized at the second electrode 164, and the non-limiting amount of the oxidized mediator is reduced at the first electrode 166 and thus the first electrode 166. ) And a concentration gradient between the second electrode 164. As described, the second test potential time interval T ₂ should be long enough so that a sufficient amount of ferricyanide can be generated at the second electrode 164. A sufficient amount of ferricyanide may be required at the second electrode 164 so that the limiting current can be measured to oxidize the ferrocyanide at the first electrode 166 during the third test potential E ₃ . The second test potential time interval T ₂ may range from about 0 seconds to about 60 seconds, preferably from about 1 second to about 10 seconds, most preferably from about 2 seconds to about 5 seconds Can be.

FIG. 7B shows the oxidation current during the relatively small peak i _pb at the start of the second test potential time interval T ₂ and then during the second test potential time interval (eg, in the range of about 1 second to about 4 seconds). The gradual increase in absolute value is shown. Small peaks occur due to the initial depletion of the reduced medium in about 1 second. The gradual increase in oxidation current is due to the generation of ferrocyanide by the reagent layer 72 and then its diffusion to the second electrode 164.

After the second potential time interval T ₂ has elapsed, the test instrument 100 ranges from a third test potential time interval T ₃ (eg, from about 4 seconds to about 5 seconds, as shown in FIG. 6). ), A third test potential E ₃ (eg, about +300 mV, as shown in FIG. 7A) may be applied between the first electrode 166 and the second electrode 164. During the third test potential time interval T ₃ , the test instrument 100 may measure a third transient current, which may be referred to as i _c (t). The third test potential E ₃ may be a sufficiently positive value of the mediator redox potential such that the limiting oxidation current is measured at the first electrode 166. For example, when ferricyanide and / or ferrocyanide are used as mediators, the size of the third test potential E ₃ may range from about 0 mV to about 600 mV, preferably from about 100 mV to It may range from about 600 mV, more preferably about 300 mV.

The second test potential time interval T ₂ and the third test potential time interval T ₃ may each range from about 0.1 second to about 4 seconds. In the example shown in FIG. 7A, the second test potential time interval T ₂ was about 3 seconds and the third test potential time interval T ₃ was about 1 second. As described above, the open circuit potential time period may be allowed to pass between the second test potential E ₂ and the third test potential E ₃ . Alternatively, the third test potential E ₃ may be applied after the application of the second test potential E ₂ . Note that the first, second or third transient current can generally be referred to as cell current or current value.

The third test potential time interval T ₃ may be long enough to monitor the diffusion of the reduced mediator (eg, ferrocyanide) near the first electrode 166 based on the magnitude of the oxidation current. During the third test potential time interval T ₃ , the limiting amount of the reduced medium is oxidized at the first electrode 166, and the non-limiting amount of the oxidized medium is reduced at the second electrode 164. The third test potential time interval T ₃ may range from about 0.1 seconds to about 5 seconds, preferably from about 0.3 seconds to about 3 seconds, most preferably from about 0.5 seconds to about 2 seconds Can be.

FIG. 7B shows the relatively large peak i _pc at the beginning of the third test potential time interval T ₃ and then decrease to steady state current. In one embodiment, both the first test potential E ₁ and the second test potential E ₂ have a first polarity, and the third test potential E ₃ has a second polarity opposite to the first polarity. Have However, the Applicant noted that the polarity of the first, second and third test potentials may be selected depending on how the analyte concentration is determined and / or on how the test sample and control solution are distinguished.

Capacitance  Measure

In some embodiments, capacitance can be measured. Capacitance measurement can essentially measure the ionic bilayer capacitance resulting from the formation of an ion layer at the electrode-liquid interface. The magnitude of the capacitance can be used to determine whether the sample is a control solution or a blood sample. For example, when the control solution is in the reaction chamber, the magnitude of the measured capacitance may be greater than the magnitude of the capacitance measured when the blood sample is in the reaction chamber. As described in more detail below, measured capacitances can be used in various methods to correct the effect of changes in the physical properties of electrochemical cells on measurements made using electrochemical cells. For example, the measured change in capacitance can be related to at least one of the lifetime of the electrochemical cell and the storage conditions of the electrochemical cell.

By way of non-limiting example, methods and mechanisms for performing capacitance measurements on test strips can be found in US Pat. Nos. 7,195,704 and 7,199,594, each of which is incorporated herein by reference in its entirety. In one exemplary method for measuring capacitance, a test voltage having a constant component and an oscillation component is applied to a test strip. In such a case, the final test current may be mathematically processed as described in more detail below to determine the capacitance value.

In general, when the limit test current occurs at a working electrode with a well defined area (ie, area that does not change during capacitance measurement), the most accurate and precise capacitance measurement in the electrochemical test stream can be performed. A well defined electrode area that does not change over time can occur when there is an airtight seal between the electrode and the spacer. The test current is relatively constant when the current does not change rapidly due to glucose oxidation or electrochemical breakdown. Alternatively, any time function when the increase in signal that can be seen to be due to glucose oxidation is effectively balanced by a decrease in signal accompanied by electrochemical breakdown can also be a suitable time interval for measuring capacitance. have.

The area of the first electrode 166 may potentially change over time after administration with the sample as the sample seeps between the spacer 60 and the first electrode 166. In an embodiment of the test strip, the reagent layer 72 may have an area larger than the cutout area 68 that allows a portion of the reagent layer 72 to be between the spacer 60 and the first electrode layer 66. Under certain circumstances, interposing a portion of the reagent layer 72 between the spacer 60 and the first electrode layer 66 may cause the wet electrode area to increase during the test. As a result, leakage may occur during the test that causes the area of the first electrode to increase with time, which may then distort the capacitance measurement.

In contrast, the area of the second electrode 164 may be more stable with time compared to the first electrode 166 because no reagent layer exists between the second electrode 164 and the spacer 60. . Thus, the sample is less likely to seep out between the spacer 60 and the second electrode 164. Capacitance measurements using the limiting test current at the second electrode 164 can thus be more precise since the area does not change during the test.

As described above and as shown in FIG. 7A, once liquid is detected in the test strip, the first test potential E ₁ (eg, about −20 mV, as shown in FIG. 7A) is obtained. It can be applied between the electrodes for about 1 second to monitor the filling behavior of the liquid and to distinguish between the control solution and the blood. In equation 1, the test current is used from about 0.05 to about 1 second. This first test current E ₁ may be relatively low such that the distribution of ferrocyanide in the cell is distributed as little as possible by the electrochemical reactions occurring at the first and second electrodes.

A second test potential E ₂ with a larger absolute magnitude (eg, about −300 mV, as shown in FIG. 7A) may be used to test the limit current at the second electrode 164. It can be applied after the potential E ₁ . The second test potential E ₂ may comprise an AC voltage component and a DC voltage component. The AC voltage component can be applied at a predetermined time after application of the second test potential E ₂ , and can also be sine pile with a frequency of about 109 hertz and an amplitude of about +/- 50 millivolts. In a preferred embodiment, the preferred time may range from about 0.3 seconds to about 0.4 seconds after application of the second test potential E ₂ . Alternatively, the predetermined time may be a time at which the transient test current has a slope of about zero as a function of time. In another embodiment, the predetermined time may be the time required for the peak current value (eg, i _pb ) to collapse by about 50%. For the DC voltage component, this can be applied at the start of the first test potential. The DC voltage component can be of sufficient magnitude to generate a limiting test current at the second electrode, for example about -300 mV relative to the second electrode.

According to FIG. 4B, the reagent layer 72 is not coated on the second electrode 164, which causes the magnitude of the absolute peak current i _pb to be relatively low compared to the magnitude of the absolute peak current i _pc . . Reagent layer 72 may be configured to produce a reduced mediator in the presence of the analyte, and the amount of reduced media proximate to the first electrode may contribute to a relatively high absolute peak current i _pc . In one embodiment, at least the enzymatic portion of the reagent layer 72 may be configured to not substantially diffuse from the first electrode to the second electrode when the sample is introduced into the test strip.

The test current after i _pb tends to settle into a flat region in approximately 1.3 seconds, and then the reduced medium produced at the first electrode 166, which can be coated with the reagent layer 72, is then reacted with the reagent layer 72. ) Is increased again as it diffuses into the second electrode 164 which is not coated. In one embodiment, capacitance measurement may be performed in a relatively flat region of the test current value, which may be performed from about 1.3 seconds to about 1.4 seconds. In general, if the capacitance is measured one second ago, the capacitance measurement may interfere with the relatively low first test potential E ₁ , which may be used to measure the first transient current i _a (t). For example, an oscillating voltage component of order ± 50 mV superimposed on a −20 mV constant voltage component may cause significant disturbance of the measured test current. The anti-vibration voltage component not only interferes with the first test potential E ₁ , but can also significantly disturb the test current measured in about 1.1 seconds, which in turn can interfere with the calibration for the antioxidant. After a number of tests and experiments, surprisingly measuring the capacitance from about 1.3 seconds to about 1.4 seconds results in accurate and precise measurements that do not interfere with the control solution / blood discrimination test or blood glucose algorithm.

After the second test potential E ₂ , a third test potential E ₃ (eg, about +300 mV, as shown in FIG. 7A) is applied so that the test current is coated with the reagent layer 72. Which may be measured at the first electrode 166. The presence of the reagent layer on the first electrode can allow the passage of liquid between the spacer layer and the electrode layer, which can cause the electrode area to be increased.

As shown in FIG. 7A, in an exemplary embodiment, a 109 Hz AC test voltage (± 50 mV between peaks) may be applied for two cycles during a time interval t _cap . The first cycle can be used as an adjustment pulse and the second cycle can be used to determine capacitance. Capacitance estimates can be obtained by summing test currents over portions of alternating current (AC) waves, subtracting direct current (DC) offsets, and normalizing the results using the AC test voltage amplitude and AC frequency. This calculation provides a measure of the capacitance of the strip governed by the strip sample chamber when filled with the sample.

In one embodiment, the capacitance is the test current over one quarter of the AC wave on each side of the time point at which the input AC voltage crosses the DC offset, i.e., the time point at which the AC component of the input voltage is zero (zero crossing point). Can be measured by summing. The origin of the way in which this translates to the measurement of capacitance is explained in more detail below. Equation 1 can show the test current magnitude as a function of time for a time interval t _cap .

Where i _o + st represents the test current induced by a constant test voltage component. In general, the DC current component is considered to change linearly with time (due to the ongoing glucose response to produce ferrocyanide) and is therefore represented by a constant i ₀ , which is time zero (zero crossings). Point), and the gradient of s, ie the DC current, changes with time. The AC current component is represented by Isin (ωt + φ), where I is the amplitude of the current wave, ω is its frequency, and φ is its phase shift relative to the input voltage wave. The term ω can also be expressed as 2πf, where f is the frequency of the AC wave in Herz. Further, term I can be expressed as shown in equation (2).

는 복소 임피던스의 크기이다. 항

는 또한 수학식 22에 나타난 바와 같이 표현될 수도 있다.Where V is the amplitude of the applied voltage signal,

Is the magnitude of the complex impedance. term

May also be expressed as shown in equation (22).

Where R is the real part of the impedance and C is the capacitance.

Equation 1 may be integrated from a quarter wavelength before the zero crossing point to a quarter wavelength after the zero crossing point to calculate Equation 4.

This can be simplified to equation (5).

Substituting Equation 2 into Equation 1, then substituting Equation 4 and rearranging, Equation 6 is obtained as follows.

The integral term of Equation 6 can be approximated using the sum of the currents shown in Equation 7.

Here, the test current i _k is summed from the quarter wavelength before the zero crossing point to the quarter wavelength past the zero crossing point. When Equation 7 is substituted for Equation 6, Equation 8 is obtained.

Here, the DC offset current i _o can be obtained by averaging the test current over one full sine cycle around the zero crossing point.

In another embodiment, capacitance measurements can be obtained by summing currents around the maximum AC component of the current, not around the voltage zero crossing point. Thus, in equation (7), rather than the sum of quarter wavelengths on each side of the voltage zero crossing point, the test current can be summed at quarter wavelengths around the current maximum. This is equivalent to assuming that the circuit element responding to AC excitation is a pure capacitor and so φ is π / 2. Therefore, Equation 5 may be reduced to Equation 9.

This is believed to be a valid assumption in this case, since the uncoated electrode is polarized so that the DC or real component of the current flow is independent of the voltage applied over the range of voltages used for AC excitation. Thus, the real part of the impedance corresponding to AC excitation is infinite, meaning a pure capacitive element. In this case, Equation 9 may be used together with Equation 6 to calculate a simplified capacitance equation that does not require integration approximation. The real result is that the capacitance measurement is more accurate when summing currents around the maximum AC component of the current and not around the voltage crossing point.

CS / Blood differentiation test

In some examples, control solution (CS) / blood differentiation tests can be performed. If the CS / blood discrimination test determines that the sample is blood, then a series of steps may be performed, including application of the blood glucose algorithm, red blood cell volume correction, blood temperature correction and error check, and CS / blood discrimination test. If it is determined that the sample is CS (ie, non-blood), then a series of steps may be performed, which may include application of the CS glucose algorithm, CS temperature correction, and error check. If no error exists, then the test instrument outputs glucose concentration, but if an error exists, the test may output an error message.

In one embodiment, the properties of the control solution (CS) are used to distinguish the control solution from the blood. By way of example, the presence and / or concentration of redox species in the sample, reaction kinetics and / or capacitance can be used to distinguish the control solution from the blood. The methods disclosed herein can include calculating a first reference value indicative of redox concentration in the sample and a second reference value indicative of the reaction rate of the reagent with the sample. In one embodiment, the first reference value is the interference oxidation current and the second reference value is the reaction completion index.

In one embodiment, the CS / blood discrimination test may include a first reference value and a second reference value. The first value can be calculated based on the current value within the first time interval T ₁ , and the second reference value is the current during both the second time interval T ₂ and the third time interval T ₃ . Can be based on a value. In one embodiment, the first reference value can be obtained by performing a summation of the current values obtained during the first time transient current when using the test voltage waveform of FIG. 7A. As a non-limiting example, the first reference value i _sum may be represented by Equation 10.

Where i _sum is the _sum of the current values and t is the time. The second reference value, sometimes referred to as the residual response index, can be obtained by the ratio Y of the current values during the second time interval and the third time interval as shown in equation (11).

Where abs represents an absolute value function and 3.8 and 4.15 represent the time in seconds of the second and third time intervals, respectively, for this particular example.

The discrimination criterion may be used to determine whether the sample is a control solution or blood based on the second reference value of Equation 11 and the first reference value of Equation 10. For example, the first reference value of Equation 10 may be compared to a predetermined threshold, and the second reference value of Equation 11 may be compared to a predetermined threshold function. The predetermined threshold may be about 12 microamps as an example. The predetermined threshold function may be based on a function using the first reference value of equation (10). More specifically, as illustrated in Equation 12 where the calculated value of each i _sum in Equation 10 is represented by X, the predetermined threshold function F _pdt may be as follows.

Z may be, for example, a constant such as about 0.2. Thus, the CS / blood discrimination test is performed when i _sum is equal to or greater than a predetermined threshold, eg, about 12 microamps, as shown in FIG. 10, and a second time interval as shown in equation (11) and Samples can be distinguished as blood if the ratio Y of the current value during the third time interval is less than the value of the predetermined threshold function F _pdt , otherwise the sample is a control solution.

Blood sugar algorithm

If the sample is distinguished as a blood sample, the blood glucose algorithm may be performed on the test current value. Assuming that the test strip has an opposing face or face arrangement as shown in FIGS. 1A-4B and the potential waveform is applied to the test strip as shown in FIG. 7A or 8A, the glucose concentration [G] It can be calculated using a glucose algorithm as shown in equation (13).

In Equation 13, [G] is the glucose concentration, i ₁ is the first current value, i ₂ is the second current value, i ₃ is the third current value, and terms p, Z and a are empirically derived. Calibration constants. The origin of Equation 13 was filed on September 30, 2005, entitled "Method and Apparatus for Rapid Electrochemical Analysis," which is hereby incorporated by reference in its entirety. And pending US patent application publication no. 2007/0074977 (US application Ser. No. 11 / 240,797). All test current values (eg, i ₁ , i ₂ and i ₃ ) in Equation 13 use the absolute value of the current. The first current value i ₁ and the second current value i ₂ are calculated from the third transient current, and the third current value i ₃ is calculated from the second transient current. It is noted that the names "first", "second" and "third" are selected for convenience and do not necessarily reflect the order in which the current values are calculated. In addition, all current values (eg, i ₁ , i ₂ and i ₃ ) declared in equation (13) use the absolute value of the current. In one embodiment, i ₂ may be based on one or more current values collected during the third transient, and i ₃ may be based on one or more current values collected during the second transient. In another embodiment, i ₂ may be based on one or more current values collected around the endpoint of the third transient and i ₃ may be based on one or more current values collected around the time of the second transient. . Both i ₂ and i ₃ can be calculated using summation, integration or average for a portion of each time interval.

In another embodiment, term i ₁ may be defined to include peak current values from the second and third transients to enable more accurate glucose concentrations as shown in equation (14).

The term i _pb represents the peak current value for the second test potential time interval T ₂ , and the term i _pc represents the peak current value for the third test potential time interval T ₃ . The term i _ss is an estimate of the steady state current, which is expected to occur long time after application of the third test potential E _{3 in} the absence of an ongoing chemical reaction. Some examples of methods for calculating i _ss can be found in US Pat. Nos. 5,942,102 and 6,413,410, each of which is incorporated herein by reference in its entirety. The use of peak current values to take into account interferences in physiological samples is referred to herein as a method and apparatus for analyzing samples in the presence of interferences. Analyzing a Sample in the Presence of Interferents. "US Patent Application Publication No. 2007/0227912, filed March 31, 2006 (US Patent Application No. 11 / 278,341).

In one embodiment, equations (13) and (14) can be used together to calculate the glucose concentration for each blood or control solution. In another embodiment, the algorithms of Equations 13 and 14 can be used for blood having a first set of calibration factors (ie, a, p, and Z), and the second set of calibration factors for the control solution. Can be used. When using two different sets of calibration factors, the methods described herein for differentiation between test fluids and control solutions can improve the effectiveness of analyte concentration calculations.

The examples illustrated in FIGS. 7A and 7B show the polarity of the first and second applied voltages as negatives and the polarity of the third applied voltages as positives when the electrode not coated with a reagent acts as a reference electrode for voltage measurement. . However, the applied voltage may be of a polarity opposite to the sequence illustrated in FIG. 7A when the electrode coated with the reagent serves as a reference electrode for voltage measurement. For example, in the preferred embodiment of FIGS. 8A and 8B, the polarity of the first and second applied voltages is positive and the polarity of the third applied voltage is negative. In both cases, the calculation of glucose is the same, because an electrode not coated with the reagent acts as an anode during the first and second applied voltages, and the electrode coated with the reagent acts as an anode during the third applied voltage. Because it works.

In addition, if the test instrument determines that the sample is a control solution (as opposed to blood), the test instrument may store the resulting glucose concentration of the control sample so that the user can consider separate test sample concentration data from the control solution data. have. As an example, the glucose concentration for the control solution may be stored in a separate database, flagged, and / or discarded (ie, not stored or stored for a short time).

Another advantage of recognizing the control solution is that the test instrument can be programmed to automatically compare the results of the test of the control solution (eg, glucose concentration) to the expected glucose concentration of the control solution. As an example, the test instrument may be preprogrammed with the expected glucose level (s) for the control solution (s). Alternatively, the user can enter the expected glucose concentration for the control solution. When the test instrument recognizes the control solution, the test instrument can compare the expected glucose concentration with the measured control solution glucose concentration to determine if the instrument is functioning properly. If the measured glucose concentration is outside the expected range, the test instrument may output an alarm message to alert the user.

Charge time calibration

In some embodiments, the analyte concentration may be corrected based on the fill time of the sample. One example of such a method is Ronald, filed December 30, 2009, which is hereby incorporated by reference in its entirety. Ronald C. Chatelier and Alastair M. Co-Mooring, titled Alastair M. Hodges, is "Systems, Devices and Methods for Improving Accuracy of Biosensors Using Fill Time". Is disclosed in the pending patent application (Application No. 12 / 649,594). In this exemplary method, the sample is introduced into an electromagnetic cell of a sample analysis device having a working electrode and a counter electrode. An electropotential is applied between the working electrode and the counter electrode of the electrochemical cell, for example the charge time of the sample into the capillary space of the electrochemical cell can be determined. The prepulse time can be calculated at least in terms of the charging time of the sample, and the electrical potential can be applied between the working electrode and the counter electrode for the same length of time as the prepulse time. Thereafter, the concentration of the analyte in the sample is determined. By calculating the prepulse time in terms of filling time, more accurate results for the analyte concentration can be achieved. By way of example, errors such as varying red blood cell volume levels across the sample can be considered, thereby leading to a more accurate determination of the concentration of the analyte in the sample. In alternative embodiments for detecting the concentration of an analyte in a sample, the error may be corrected based on the determined initial fill rate, not the determined fill time. An example of such a method is Mr. Ronald, filed December 30, 2009, the entirety of which is incorporated herein by reference. Ronald C. Chatelier, Dennis Rylatt, Linda Raineri and Alastair M. The invention of Alastair M. Hodges is entitled "Systems, Devices and Methods for Measuring Whole Blood Haematocrit Based on Initial Fill Velocity". A co-pending patent application (Application No. 12 / 649,509) is disclosed.

Temperature compensation

In some embodiments of the systems and methods of the present invention, blood temperature correction may be applied to test current values to provide improved accuracy in analyte concentrations due to reduced effects from temperature. The method for calculating the temperature corrected analyte concentration may include measuring a temperature value and calculating a temperature correction value (C _T ). The temperature correction value C _T may be based on the temperature value and the analyte concentration, eg, glucose concentration. Thus, the temperature correction value C _T can then be used to correct the analyte concentration for the temperature.

Initially, analyte concentrations that are not corrected for temperature such as glucose concentration [G] from Equation 13 above can be obtained. In addition, temperature values can be measured. The temperature may be measured using a thermistor or other temperature reading device integrated into the test instrument, or by any number of other mechanisms or means. Subsequently, a determination may be performed to determine whether the temperature value T is greater than the first temperature threshold T ₁ . As an example, the temperature threshold T ₁ may be about 15 ° C. If the temperature value T is greater than 15 ° C., then a first temperature function may be applied to determine the temperature correction value C _T. If the temperature value T is 15 ° C. or less, then a second temperature function may be applied to determine the temperature correction value C _T.

The first temperature function for calculating the temperature correction value C _T may be in the form of Equation 15.

Where C _T is a correction value, K ₉ is a ninth constant (eg, 0.59), T is a temperature value, T _RT is a room temperature value (eg, 22 ° C.), and K ₁₀ is a tenth Constant (eg, 0.00004) and [G] is the glucose concentration. When T is approximately equal to T _RT , C _T is approximately zero. In some examples, the first temperature function may be configured to have substantially no correction at room temperature such that variation under ordinary ambient conditions is reduced. The second temperature function for calculating the second correction value C _T may be in the form of Equation 16.

Where C _T is a correction value, K ₁₁ is an eleventh constant (eg, 0.59), T is a temperature value, T _RT is a room temperature value, and K ₁₂ is a twelfth constant (eg, 0.00004) , [G] is the glucose concentration, K ₁₃ is the thirteenth constant (eg, 1.2), T ₁ is the first temperature threshold, and K ₁₄ is the fourteenth constant (eg, 0.005).

After C _T is calculated using Equation 15, a pair of truncation functions can be performed to ensure that C _T is constrained to a predetermined range to mitigate the risk of outliers. In one embodiment, C _T may be limited to have a range of −10 to +10. As an example, a determination may be performed to determine if C _T is greater than ten. If C _T is greater than 10, then C _T is set to 10. If C _T is 10 or less, then a determination is made to determine whether C _T is less than -10. If C _T is less than -10, C _T may be set to -10. If C _T is already between -10 and +10, then truncation is generally not necessary.

After C _T is determined, the temperature corrected glucose concentration can be calculated. As an example, a determination may be performed to determine whether the glucose concentration (eg, [G]) not corrected for temperature is less than 100 mg / L. When [G] is less than 100 mg / dL, Equation 17 may be used to calculate the temperature-corrected glucose concentration G _T by adding the correction value C _T to the glucose concentration [G].

If [G] is less than 100 mg / dL, then mathematics to calculate the temperature corrected glucose concentration (G _T ) by dividing C _T by 100, adding 1, and then multiplying by glucose concentration [G] Equation 18 can be used.

Once the corrected glucose concentration has been determined for the effect of temperature, the glucose concentration can be output to the display, for example.

Aging / storage calibration

In some embodiments of the methods and systems of the present invention, other correction factors may be applied to the calculated glucose concentration. This correction factor can be used to provide improved accuracy by correcting for the effect of storage conditions and / or aging on sensor performance. As an example, a parameter correlated to the physical properties of the sensor can be measured, which can be used to calculate the corrected analyte concentration. In some embodiments, the parameter correlated to the physical characteristics of the sensor may be the measured capacitance of the sensor.

The measured capacitance of a sensor, for example an electrochemical cell of the type described above in more detail, can be related in terms of aging and / or storage conditions of the sensor. As a non-limiting example, the capacitance of the electrochemical cell can be affected by the slow flow of adhesive used to make the electrochemical cell from the spacer layer into the sample reaction chamber. With the same sensor aging, especially during storage at elevated temperatures, the adhesive can flow into the reaction chamber and cover the sensor's reference and / or counter electrodes. By way of example, the adhesive can cause a reduction in the area of the electrode that can affect the accuracy of the measurements made by the sensor. In addition, the reduction of the electrode area can be correlated with the reduction of the capacitance of the sensor. Thus, the measured capacitance of the sensor can be used to calculate a correction factor that can be used to improve the accuracy of readings made using the sensor.

In one exemplary embodiment, the method for calculating the calibrated analyte concentration may include measuring the physical properties of the electrochemical cell, eg, capacitance, and calculating the calibration factor C _c . . The correction factor C _c can be based on the measured physical properties. Thus, a correction factor C _c can be used to calculate the corrected analyte concentration.

Initially, an uncorrected analyte concentration such as glucose concentration [G] can be obtained from Equation 13 above. Alternatively, analyte concentrations used in the algorithms described below may be precalibrated using any other calibration method, e.g., temperature and / or fill time corrected analyte concentrations detailed above. Have an analyte concentration. In addition, the measured capacitance of the sensor can be obtained using, for example, the capacitance measuring method described above. Subsequently, a determination may be performed to determine whether the measured capacitance value C is less than the capacitance threshold C ₁ . In some embodiments, the capacitance threshold C ₁ may be the average or ideal capacitance of sensors of the same type. If the capacitance value C is below the capacitance threshold C ₁ , and if the uncorrected (or previously calibrated) analyte concentration [G] is greater than the analyte concentration threshold [G ₁ ], When the capacitance correction function can be used to determine the correction factor (C _c ). When the capacitance value C is greater than or equal to the capacitance threshold C ₁ and / or the analyte concentration [G] that has not been calibrated (or previously calibrated) is less than or equal to the analyte concentration threshold [G ₁ ] , The correction factor C _c may be set to zero. As an example, in one embodiment, the capacitance threshold C ₁ may be about 559 nanoFarad and the analyte concentration threshold [G ₁ ], for example, the glucose concentration may be about 100 mg / dL. Thus, if the capacitance value C and / or the analyte concentration [G] has a predetermined range (s), the correction factor C _c can be determined using the capacitance correction function, otherwise The correction factor C _c can be set to zero.

Capacitance correction factor when the measured capacitance value (C) is below the capacitance threshold (C ₁ ) and the uncorrected (or previously calibrated) analyte concentration [G] is greater than the analyte concentration threshold [G ₁ ]. The capacitance correction function for calculating (C _c ) may be in the form of Equation 19.

Where C _c is the correction factor, K _c is the empirically derived constant (eg 0.152), C ₁ is the capacitance threshold (eg 559 nanoFarad) and C is the measured capacitance value.

For example, after C _c is calculated using Equation 19, a pair of truncation functions are performed to ensure that C _c is constrained to a predetermined range, thereby limiting the maximum correction applied to the data. It can reduce the risk. In one embodiment, when C _c is greater than the cutoff value, C _c may be set to the cutoff value. As an example, a determination may be performed to determine whether C _c is greater than a cutoff value, eg, five. If C _c is greater than the cutoff value, for example 5, then C _c is set to the cutoff value, for example 5. If C _c is less than or equal to the cutoff value, then cutting is generally not necessary.

After C _c is determined, the capacitance corrected glucose concentration can be calculated. For example, if the analyte is glucose, whether the uncorrected (or previously calibrated) analyte concentration [G] is less than the analyte concentration threshold [G ₁ ], eg, 100 mg / dL. Judgment may be performed to determine. If [G] is less than the analyte concentration threshold [G ₁ ], then no other correction is applied. If [G] is greater than the analyte concentration threshold [G ₁ ], then the capacitance corrected glucose concentration by dividing C _c by 100, adding 1, and then multiplying by the analyte concentration [G] Equation 20 may be used to calculate (G _c ).

The analyte concentration corrected for the effects of aging and / or storage can be determined and then the glucose concentration can be output to the display, for example.

Example 1

The development of an algorithm for calibration of the aging of a sensor used in an electrochemical system is illustrated by the following example. In the examples below, the system includes a sensor with two opposed electrodes, and the reagent is designed to react with the dried sample on one electrode. A plurality of samples is provided for analysis to test the performance of the systems, devices, and methods disclosed herein. The sample is a blood sample comprising three different levels of red blood cell volume and two different levels of glucose, each of which is known, so that a comparison of test results is a real result to determine the accuracy of the system, apparatus and method. Can be compared to. The three levels of erythrocyte volume fraction are approximately 20%, 37-45% and 60%. The two levels of glucose are approximately 250 mg / dL and 500 mg / dL. Testing three levels of red blood cell volume and two levels of glucose can confirm the accuracy of the disclosed systems, devices, and methods over a broad spectrum of concentration levels.

In this example, the first group of sensors were stored at 5 ° C. for 4 to 21 weeks. The second group of sensors was stored for 4 to 21 weeks at 30 ° C. and 65% relative humidity. The sensor was tested with the blood sample described above. During glucose measurement, the capacitance of the sensor was also calculated. In addition, sensor-based measurements were tested using the YSI 2700 clinical instrument to provide baseline measurements of glucose against which to provide NGL bias data. Figure 9 showing the NGL bias versus capacitance illustrates the data obtained in these tests. As illustrated in FIG. 9, the bias percentage is correlated with capacitance. In particular, the lower measured capacitance, as shown by the regression line in the chart, correlates with the increased negative bias.

Example 2

The result of the capacitance correction algorithm is illustrated by the following example. In this example, the data obtained from the experiment described in Example 1 was corrected based on the correction algorithm described in more detail above. Table 1 shows the improvement of glucose measurements obtained by applying the calibration algorithm, the data being within a given percentage of measurements made by the YSI 2700 clinical instrument when G≥80 mg / dL or given a number of G <80 mg / dL. Shows the percentage of bias that is within. Table 1 also shows the mean bias and mean square root bias.

Uncorrected Data Calibration data % Bias or 10 mg / dL within 10% 93.48 94.84 % Bias within 12% or 12 mg / dL 97.29 97.73 % Bias within 15% or 15 mg / dL 99.21 99.29 Average bias -1.67 -0.25 RMS bias 5.45 5.15

The capacitance corrected data in the right column of the table represents an improvement of each parameter when the glucose value is corrected using the measured capacitance.

Example 3

The results of testing the use of capacitance correction algorithms with more severely aged sensors are illustrated by the following examples. In this example, the algorithm was tried with a much larger data set of 60,864 sensors, and the sensors were stored at 5-40 ° C. The results in Table 2 show a consistent improvement in accuracy and precision when using the disclosed capacitance correction algorithm.

Uncorrected Data Calibration data % Bias or 10 mg / dL within 10% 91.09 93.14 % Bias within 12% or 12 mg / dL 95.54 96.77 % Bias within 15% or 15 mg / dL 98.47 98.94 Average bias -0.26 0.41 Global SD Bias 5.83 5.40 RMS bias 5.83 5.42 Pooled Precision 2.15 2.18 Number of tests 60,864 60,864

Example 4

The result of using the capacitance correction algorithm using a non-aging (newly manufactured) sensor at high temperature is illustrated by the following example. In this example, a new manufactured sensor was tested over the range of 5-45 ° C. The results in Table 3 show that the capacitance correction algorithm does not degrade significantly when applied over various simulated high temperature climatic conditions.

Uncorrected Data Calibration data % Bias or 10 mg / dL within 10% 96.39 96.37 % Bias within 12% or 12 mg / dL 98.73 98.71 % Bias within 15% or 15 mg / dL 99.73 99.71 Average bias -0.51 -0.49 Global SD Bias 4.68 4.68 RMS bias 4.71 4.70 Pooled Precision 2.44 2.43 Number of tests 5,178 5,178

Example 5

The results of the use of a capacitance correction algorithm using blood samples and multiple sensor manufacturing lots over an extended red blood cell volume and glucose range at room temperature are illustrated by the following examples. In this example, the sensor was tested at room temperature. The results in Table 4 also show that the capacitance correction algorithm provides accurate results over extended red blood cell volume and glucose range at room temperature.

Uncorrected Data Calibration data % Bias or 10 mg / dL within 10% 98.46 98.43 % Bias within 12% or 12 mg / dL 99.39 99.38 % Bias within 15% or 15 mg / dL 99.83 99.83 Average bias -0.02 0.12 Global SD Bias 3.81 3.84 RMS bias 3.81 3.84 Pooled Precision 1.86 1.88 Number of tests 50,997 50,997

While the invention has been described in connection with specific variations and exemplary drawings, those skilled in the art will recognize that the invention is not limited to the variations or drawings described. In addition, although the methods and steps described above represent particular events occurring in a particular order, those skilled in the art will recognize that the order of specific steps may be modified, and that such variations are in accordance with the variations of the present invention. Additionally, if possible, certain steps may be performed simultaneously in parallel processing, and may be performed sequentially as described above. Thus, to the extent that variations of the invention which correspond to the invention as defined in the claims or are within the concept of the disclosure exist, this patent is intended to cover such variations as well. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

Claims (28)

A method for determining the concentration of an analyte in a sample,
Introducing a sample comprising an analyte into an electrochemical cell of a sample analysis device to cause transformation of the analyte, wherein the electrochemical cell has a first electrode and a second electrode;
Determining a measurement of a parameter that correlates to a physical property of the electrochemical cell;
Calculating a correction factor, the correction factor being at least in terms of the parameter; And
Determining the concentration of the analyte in view of the correction factor. The method of claim 1, wherein the parameter comprises a measured capacitance of the electrochemical cell. The method of claim 2, wherein determining the measured capacitance of the electrochemical cell is:
Applying a first test voltage between the first electrode and the second electrode, wherein the first test voltage has an AC voltage component and a DC voltage component, the AC voltage component after application of the first test voltage Applying the first test voltage at a predetermined time, the DC voltage component having a magnitude sufficient to generate a limiting test current at the second electrode, the second electrode having no reagent layer coating; And
Processing the portion of the test current resulting from the AC voltage component into a capacitance value. The method of claim 1, wherein the physical property is related to at least one of the lifetime of the electrochemical cell and the storage conditions of the electrochemical cell. 5. The method of claim 4 wherein the storage condition comprises a storage temperature and a storage time. The method of claim 1, wherein the sample analysis device comprises a glucose sensor. The method of claim 1, wherein the sample analysis device comprises an immune sensor. The method of claim 1, wherein the sample comprises blood. The method of claim 8, wherein the blood is whole blood. As an electrochemical system,
An electrochemical cell having a first electrode and a second electrode;
An instrument comprising said control unit connected to said electrochemical cell such that a control unit applies a potential between said first electrode and said second electrode of said electrochemical cell,
The control unit uses the measurement to determine a measurement of a parameter that correlates to a physical property of the electrochemical cell and to calculate a calibrated concentration of the analyte in the sample. 12. The electrochemical system of claim 10, wherein said parameter comprises a measured capacitance of said electrochemical cell. 11. The electrochemical system of claim 10, wherein said physical property is related to at least one of the lifetime of said electrochemical cell and the storage conditions of said electrochemical cell. 13. The electrochemical system of claim 12, wherein said storage conditions comprise a storage temperature and a storage time. The electrochemical system of claim 10, wherein the sample comprises blood. 15. The electrochemical system of claim 14, wherein said blood comprises whole blood. A method for measuring the concentration of a calibrated analyte,
Applying a sample comprising the analyte to the test strip;
Applying a first test voltage to the sample for a first time interval between the first electrode and the second electrode sufficient to oxidize the reduced medium at the second electrode;
After application of the first test voltage, applying a second test voltage to the sample for a second time interval between the first electrode and the second electrode sufficient to oxidize the reduced medium at the first electrode; ;
Calculating a first analyte concentration in the sample based on a test current value during the first time interval and the second time interval;
Determining a capacitance of the test strip; And
Calculating a capacitance corrected analyte concentration based on the first glucose concentration and the capacitance. The method of claim 16, wherein calculating the capacitance corrected analyte concentration is:
Calculating a correction factor based on the capacitance and the first analyte concentration, wherein the capacitance corrected analyte concentration is calculated based on the first analyte concentration and the correction factor. 17. The method of claim 16, wherein determining the capacitance of the test strip is:
Applying a first test voltage between the first electrode and the second electrode, wherein the first test voltage has an AC voltage component and a DC voltage component, the AC voltage component after application of the first test voltage Applying the first test voltage at a predetermined time, the DC voltage component having a magnitude sufficient to generate a limiting test current at the second electrode, the second electrode having no reagent layer coating; And
Processing the portion of the test current resulting from the AC voltage component into a capacitance value. 17. The method of claim 16, wherein the capacitance corrected analyte concentration is calculated when the capacitance is less than a first capacitance threshold and the first analyte concentration is greater than a first analyte concentration threshold. The method of claim 16, wherein calculating the capacitance corrected analyte concentration is:
Dividing the correction factor by 100 and adding 1 to provide an intermediate term; And
And multiplying the intermediate term by the first analyte concentration to provide a capacitance corrected analyte concentration. 17. The method of claim 16,
Determining if the correction factor is greater than a correction factor threshold, and then setting the correction factor to the correction factor threshold. 17. The method of claim 16, wherein the correction factor is about zero when the capacitance is equal to a predetermined abnormal capacitance of the test strip. The method of claim 16, wherein the analyte comprises glucose. As an electrochemical system,
(a) a test strip comprising an electrical contact and an electrochemical cell configured to mate with a test instrument, wherein the electrochemical cell is:
(i) a first electrode and a second electrode in a spaced apart relationship; And
(ii) said test strip comprising an electrochemical cell comprising a reagent; And
(b) a processor adapted to receive current data from the test strip upon application of a voltage to the test strip, and further adapted to determine capacitance corrected glucose concentration based on the calculated glucose concentration and the measured capacitance. An electrochemical system comprising a test instrument comprising. 25. The electrochemical system of claim 24, wherein said test instrument comprises a data storage device comprising a glucose concentration threshold and a capacitance threshold. 25. The electrochemical system of claim 24, wherein the processor determines the capacitance corrected glucose concentration value when the measured capacitance is less than the capacitance threshold and the calculated glucose concentration is greater than the glucose concentration threshold. 25. The electrochemical system of claim 24, wherein said measured capacitance correlates to a physical property of said test strip with respect to at least one of the life of said test strip and the storage conditions of said test strip. 28. The electrochemical system of claim 27, wherein said storage conditions comprise a storage temperature and a storage time.

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