HK40013090B

HK40013090B - Analyte detection meter and associated method of use

Info

Publication number: HK40013090B
Application number: HK42020003021.1A
Authority: HK
Inventors: Iyengar Sridhar; Harding Ian; Williams Richard; Hua, (Kevin) Cai
Original assignee: Agamatrix, Inc.
Priority date: 2013-03-15
Filing date: 2020-02-20
Publication date: 2022-02-04

Description

Analyte detection instrument and related methods of use

The present application is a divisional application of an invention patent application having an application date of 2014, month 2 and day 14, application number 201480015282.0 (PCT/US2014/016452), entitled "analyte detection instrument and associated method of use".

Background

The present application relates to methods for encoding information on electrochemical test strips and methods for obtaining information encoded on test strips and meters capable of obtaining such information.

Small disposable electrochemical test strips are often used to monitor blood glucose in diabetic patients. These test strips can also be used to detect other physiological chemicals of interest and substances of abuse. In general, the test strip comprises at least two electrodes and appropriate reagents for the test to be performed, and is manufactured as a single-use disposable element. The test strip is combined with a sample, such as blood, saliva or urine, before and after insertion into a reusable meter containing a mechanism for monitoring the electrochemical signal from the test strip and processing it as an indicator of the presence/absence of the analyte or the amount of analyte determined by the test strip.

Electrochemical test meters are known in the art (e.g., for determining blood glucose levels). See, e.g., U.S. patent nos. 7771583, 7645374, 7601249, 7547382, 7517439, 7501052, 7344626, 7090764, 6662439, 6284125, 6071391, 5942102, 53522351, and 5243516, all of which are incorporated herein by reference.

Test strips often have information associated with them, such as, inter alia, calibration information, a region or country code, a product identification, a user identification, a test type (e.g., a glucose test strip or a ketone test strip), and a date of manufacture. PCT patent application serial numbers PCT/US11/51983 and U.S. patent numbers 7713392, 7695608, 7645421, 7625473, 7601299 and 4714874, all of which are incorporated herein by reference, provide strips with this and other types of information encoded on test strips and associated meters and methods for decoding information from the strips. The challenge for the manufacturer is how to encode the information on the test strip and how to obtain the encoded information in a cost-effective, reliable, secure and robust manner. The present invention provides systems and methods that address these difficulties.

Summary of The Invention

The present invention provides methods for encoding information on a test strip and methods for obtaining information encoded on an electrochemical test strip and meters capable of obtaining such information. The method of obtaining information employs the step of determining a value indicative of the double layer capacitance or equivalent capacitance of the test strip after sample introduction. This value can then be converted into information about the characteristics of the test strip that was encoded on the test strip prior to sample introduction.

The inventors have found that the double layer and/or equivalent capacitance of the strip is a variable that can be controlled/varied to encode information onto the test strip. Furthermore, the inventors have found that determining a value indicative of the double layer capacitance or equivalent capacitance of the strip allows information to be obtained when a sample is present in the sample space and this value is then converted to information reflecting the characteristics of the test strip prior to introduction of the sample. The encoded information can then be used in subsequent analysis or correction steps to adjust a calculated value (e.g., a value obtained in the determination or detection of an analyte) or it can be used to generate and/or display an erroneous result or information to a user.

In a first aspect of the invention, a method is provided for obtaining information encoded on an electrochemical test strip having at least two electrodes in a sample space. Information was encoded on the strip prior to introduction of the sample. The method comprises the following steps:

(a) the sample is introduced into the sample space such that the sample is in contact with both electrodes within the sample space.

(b) Determining a value representative of the double layer capacitance or equivalent capacitance of the test strip, and

(c) converting the value determined in step (b) into information reflecting characteristics of the test strip prior to introduction of the sample,

thereby obtaining information encoded on the electrochemical test strip.

In a second aspect of the invention, a method is provided for detecting an analyte in a sample in contact with two electrodes within a sample space of an electrochemical test strip. The test strip has characteristic information encoded thereon prior to introduction of the sample. The method comprises the following steps:

(a) introducing the sample into the sample space such that the sample is in contact with the two electrodes within the sample space,

(d) detecting an analyte in a sample disposed in the sample space, and

(e) modifying the result of step (d) using the characteristic information converted in step (c).

The present invention also provides a meter for receiving an electrochemical test strip having electrodes and providing a determination of an analyte in a sample applied to the electrochemical test strip when received in the meter. The meter includes:

(a) a housing having an opening for receiving an electrochemical test strip, the test strip having characteristic information encoded thereon,

(b) a communication device for receiving user input and communicating the result to a user, an

(c) A circuit for determining double layer capacitance or equivalent capacitance on a test strip having two electrodes in a sample space containing a sample received in a meter; circuitry for converting the measured double layer capacitance or equivalent capacitance to information reflecting characteristics of the test strip prior to introduction of the sample; and a circuit for determining an analyte in the sample space of the test strip.

In another aspect of the invention, a measurement system is provided. The system comprises a meter as described above and a test strip having two electrodes in the sample space, wherein the test strip is arranged in a groove in the housing of the meter.

Brief Description of Drawings

FIG. 1 is a flow chart showing the steps of an embodiment of the present invention.

Fig. 2-6 show different lookup tables containing capacitance values and associated characteristic information.

Fig. 7 shows an external view of a meter according to the invention.

Detailed Description

When the sample space of the test strip is filled with sample, or alternatively when the electrodes (or dominant electrodes) within the sample space are entirely covered by the sample, then the determination of the value representing the double layer capacitance or equivalent capacitance of the test strip can be converted into characteristic information encoded on the test strip prior to sample introduction. Information can be encoded on the test strip by varying variables within the sample space that affect the equivalent and/or double layer capacitance of the strip as the sample covers the electrodes in the sample space. These variables include: controlling or changing the effective area of the electrodes within the spatial sample of the test strip, controlling or changing the structural material of the electrodes, electrode surface modification, controlling or changing the type or concentration of ions (e.g., type and amount of ions, such as those present in the reagent as salts), controlling or changing the type or concentration of the medium.

Definition of

As used in the specification and claims of this application, the following definitions shall apply:

(a) "analyte" refers to a material of interest that may be present in a sample. In the present application, the examples use glucose as the analyte, but the invention is independent of both the type and amount of analyte. Thus, the application of the glucose detection system should be seen as a specific and non-limiting embodiment only.

(b) "determination of an analyte" refers to qualitative, semi-quantitative, and quantitative processes for evaluating a sample. In a qualitative assessment, the results indicate whether an analyte is detected in the sample. In a semi-quantitative evaluation, the results indicate whether the analyte is present above some predefined threshold. In quantitative evaluation, the result is a numerical indication of the amount of analyte present.

(c) "bilayer" refers to a charged layer formed at the conductor/electrolyte interface, resulting in the formation of a localized layer near the solid surface that neutralizes the mirror charge in the conductor due to ion adsorption on the conductor surface. When a liquid sample is present in contact with the electrodes, a bilayer forms at each electrode in the electrochemical test strip, whether or not an electrical potential is applied. However, the amount of charge in the bilayer is a function of the electrode potential. The double layer structure behaves essentially as a capacitor.

(d) "double layer capacitance" is the capacitance of a double layer. It may be an integrating capacitor (in which case it may be used in equation C_int= I Δ t/Δ V) or differential capacitance (in this case, it can be expressed by the formula C_dif= I/(dV/dt) where I is the flow current, t is the time and V is the voltage). As described in Harding (U.S. patent No. 7547382), in some cases the measured double layer capacitance may be dominated by one electrode, for example if one electrode has a substantially larger area, or if ions of one charge are adsorbed in the sample than ions of another chargeIn the case of stronger ions. The double layer capacitance measured in these cases is within the scope of the present invention, but it should be noted that where one of the electrodes dominates, the geometry of the fill is such that the double layer capacitance of the dominant electrode represents the fill state of the electrochemical strip. In the case of measuring the double layer capacitance of a test strip, it is preferably determined in accordance with the teachings of U.S. patent No. 7547382, Harding et al, which is incorporated herein by reference for all purposes.

(e) "double layer charging" is the process of increasing the charge stored in the double layer due to the applied potential. The phrase "double layer charging at an electrode" refers to charging at both electrodes or charging at the dominant electrode.

(f) "double layer discharge" is the process of reducing the charge stored in the double layer by disconnecting the applied potential. The phrase "double layer discharge at an electrode" refers to a discharge at both electrodes or at the dominant electrode.

(g) "equivalent capacitance" is understood herein to mean the total equivalent capacitance between electrodes (e.g., across a sample space electrochemical test strip when the electrodes are in contact with a sample in the sample space) when an electrical potential is applied between the electrodes. The "equivalent capacitance" of the test strip is the combination of the double layer capacitance of the strip and the faraday capacitance of the strip. In the case of equivalent capacitance measurements, it is preferably determined in accordance with the teachings of either or both of U.S. patent No. 6872298 and/or U.S. patent application serial No. 09/974597 (as published in US 2003/0098233).

(h) As used herein, "faraday capacitance" refers to the pseudocapacitive component of the equivalent capacitance of the test strip and represents the electrochemical reaction process that occurs on the electrode surface.

(i) An "electrochemical test strip" or simply "test strip" refers to a strip having at least two electrodes in a sample space and any necessary reagents for determining an analyte in a sample disposed between the electrodes. In a preferred embodiment, the electrochemical test strip is disposable after a single use and has electrical connections for connection to a separate and reusable meter containing electronics for applying an electrical potential, analyzing a signal, and displaying a result. In another embodiment, the electrochemical test strip includes a plurality of sample spaces and electrodes disposed within those sample spaces. In this latter embodiment, the "test strip" may be used multiple times with the sample introduced into one or more of the sample spaces at different times.

(j) "opposing electrodes" is a pair of electrodes that are parallel to each other but arranged in a single plane. It is preferred that some or all of the opposing surfaces of a pair of opposing electrodes overlap such that the potential gradient and current flow between the electrodes is in a direction substantially perpendicular to the opposing surfaces. The opposite electrode differs from a side-by-side electrode in which both electrode surfaces lie in the same plane and in which the potential gradient and the current flow are substantially parallel to the surfaces of the electrodes. The invention may be used with opposing or side-by-side electrodes as well as other geometric arrangements.

(k) "information encoded on a test strip" is any type of information detailing the characteristics of the test strip that is intentionally, unintentionally, or inherently encoded on the test strip during manufacture or prior to introduction of a sample to be analyzed. Information is encoded on the test strip prior to introducing the sample into the sample space. Information can be encoded on the test strip by varying variables within the sample space that affect the equivalent and/or double layer capacitance of the strip as the sample covers the electrodes in the sample space. These variables include: controlling or changing the effective area of the electrodes within the spatial sample of the test strip, controlling or changing the structural materials of the electrodes, electrode surface modification, controlling or changing the type or concentration of ions (e.g., type and amount of ions, such as those present in the reagent as salts), controlling or changing the type or concentration of the medium. Encoding information into the test strip may be accomplished, for example, by forming electrodes in a sample space having a specified effective area during manufacture, or may be accomplished as a post-production step by altering the effective area of the electrodes in the sample space by etching, stamping, ablating, scoring or otherwise removing conductive material from the electrodes in the sample space. A non-limiting exemplary list of types of characteristic information that may be encoded on a test strip includes: calibration information, region or country code, product identification, user identification, test type (e.g., glucose test strip or ketone test strip), and date of manufacture.

(l) Obtaining information is herein understood to mean decoding, reading, converting, retrieving or otherwise obtaining or determining the information encoded on the test strip.

(m) conversion herein is understood to mean the use of the values determined in a set of steps to provide information about the test strip that is representative of the characteristics of the test strip prior to introduction of the sample into the test strip. For example, a measurement representing the double layer capacitance or equivalent capacitance of the test strip may be reconciled with a lookup table stored in or obtained by the meter. The lookup table may have one or more ranges of values that indicate various characteristic information of the test strip.

(n) herein "a value representing a double layer capacitance or an equivalent capacitance" is understood to mean the actual measured capacitance or a separate value (e.g. an electrical signal or some other value) containing information about the capacitance of the strip.

(o) herein "active area of the electrode" is understood to mean the conductive part of the electrode or the dominant electrode which is in contact with the sample in the sample space and which can be electrically connected to the meter. The "active area" includes the conductive portion of the electrode that is exposed to the sample when present in the sample space. An "active area" includes a conductive portion exposed to a sample located within a two-dimensional planar footprint (e.g., length, width, radius, etc.) and an electrode conductive portion exposed to a sample located in a third dimension (e.g., depth or thickness), such as a pit, slit, and/or well of an electrode.

Reference throughout the specification to "one embodiment," "another embodiment," "an embodiment," "some embodiments," and so forth, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.

Method of obtaining encoded information from a test strip:

in a first aspect, the present invention provides a method for obtaining information encoded on an electrochemical test strip. The test strip has at least two electrodes disposed within the sample space and information is encoded on the test strip prior to introduction of the liquid sample. As shown in fig. 1, the method comprises the following steps:

(b) determining a value representative of the Double Layer Capacitance (DLC) or Equivalent Capacitance (EC) of the test strip, and

thereby obtaining information encoded on the electrochemical test strip.

Step (b) of determining a value representative of the double layer capacitance or equivalent capacitance of the test strip is known in the art and is not particularly limited herein. The measured value may be the actual value of the double layer capacitance of the test strip or its equivalent capacitance, or it may be a value or signal representative of either or both of these capacitance values.

The prior art references discussed herein use the double layer capacitance or equivalent capacitance of the test strip to determine whether a sufficient amount of sample has been applied to the sample space and configure the sample space to perform an electrochemical determination of the analyte. It is disclosed in these references that the sample volume can be determined as a function of the electrode area wetted by the sample and the spacer layer thickness and/or electrode spacing. These references each describe and employ different capacitance measurements for determining the area of an electrode wetted by a sample in a sample space and thus provide different methods of determining the sufficiency of a sample in a sample space. Any of these methods for determining double layer capacitance or equivalent capacitance may be employed to achieve step (b) of the present invention.

For example, U.S. patent No. 7547382, Harding et al, which is incorporated herein by reference, discloses a number of different methods for measuring the double layer capacitance of a test strip. Harding uses the double layer capacitance of the strip to determine whether sufficient sample is present in the sample space to perform an electrochemical determination of the analyte in the sample.

Harding describes that the double layer capacitance of a test strip with a sample in the sample space can be determined using the following steps:

(i) a potential difference is applied between the electrodes of the test strip,

(ii) the applied potential is disconnected and optionally a second potential is reapplied,

(iii) observing the current generated and determining from the observed current the double layer charge or discharge at the electrode, and

(iv) observing the voltage change after the applied potential is cut off, and

(v) the double layer capacitance of the test strip is determined from the measured double layer charge or discharge and the observed voltage change.

Harding uses these steps to determine the double layer capacitance of the test strip, which is the integral or differential capacitance of the test strip.

In the case of determining a value representative of the equivalent capacitance of a test strip, it may be determined in accordance with the teachings of either or both of U.S. patent No. 6872298 and/or U.S. patent application serial No. 09/974597 (as published in US 2003/0098233), both of which list Kermani as the inventor and are incorporated herein by reference. In these references, Kermani uses the equivalent capacitance of the test strip when a sample is present in the sample space to determine whether sufficient sample is present in the sample space to perform an electrochemical determination of an analyte in the sample. In US2003/0098233, Kermani describes a method of determining the equivalent capacitance of a test strip comprising the steps of:

(i) an alternating voltage of a selected amplitude and a selected frequency is applied between the electrodes of the test strip,

(ii) measuring the current resulting from the application of the potential in step (I), and

(iii) (iii) determining the equivalent capacitance of the test strip from the current measured in step (ii), wherein said equivalent capacitance comprises both the double layer capacitance and the faraday capacitance of the test strip.

In U.S. patent No. 6872298 to Kermani, he describes another method of determining the equivalent capacitance of a test strip which includes the steps of:

(i) applying a potential difference between the electrodes of the test strip, thereby charging the test strip, wherein a double layer capacitance is created within the test strip and a voltage is generated by charging the test strip,

(ii) the voltage caused by charging the test strip is converted into an oscillating voltage with a period proportional to the resulting double layer capacitance,

(iii) observing the oscillating voltage, an

(iv) The equivalent capacitance of the test strip was determined from the observed oscillating voltage.

As discussed above, step (b) may be suitably implemented using the teachings of the prior art and is not particularly limited herein.

In order to obtain the most accurate (b) determination of the value representing the double layer capacitance or equivalent capacitance of the strip for the purpose of obtaining the information encoded on the test strip prior to introduction of the sample, the sample space is preferably completely filled with the sample. For example, the sample is preferably disposed between the electrodes (or the dominant electrode) and completely covered. This may indicate that the sample space is completely filled with sample or this may indicate that the sample space is not completely filled with sample, but that the sample covers the electrodes. In preferred embodiments, the methods, strips, meters and meter/strip combinations of the invention further comprise structure or function to determine whether the sample completely covers the electrode (or dominates the electrode) within the sample space. This step may occur at any time after the sample is introduced, however, as shown in FIG. 1, this preferably occurs before the capacitance value of the strip is determined. Methods and apparatus useful for fill detection are well known in the art and are not particularly limited herein. For example, US4929426 discloses the use of impedance electrodes through which the sample flows when the sample chamber is filled, while US5582697, US6212417 and US6299757 disclose the use of a third electrode that can be used for fill detection, all of which are incorporated herein by reference. US6743635, incorporated by reference, discloses a four-electrode process comprising separate filled detection anodes and cathodes. US5997817, incorporated by reference, discloses a test strip with a window through which the sample is viewable and a line "filled to this" to assess the sufficiency of the sample.

Once a value representing the double layer capacitance or equivalent capacitance of the test strip is determined, this value (c) can be converted into information reflecting the characteristics of the test strip prior to introduction of the sample. As shown in fig. 2 and 3, the conversion step preferably reconciles (e.g., references) the measured double layer capacitance or equivalent capacitance of the test strip with a look-up table. In FIG. 2, the lookup table correlates the range of capacitance values to the area identification or country code of the test strip. In FIG. 3, a lookup table correlates a range of capacitance values with the type of analyte for which the test strip is designed to measure. In FIG. 4, the lookup table correlates a range of capacitance values with calibration information for the test strip. In FIG. 5, the lookup table correlates a range of capacitance values to product identification for the test strip. In fig. 6, a lookup table associates ranges of capacitance values with production or expiration years.

Converting the value of the double layer capacitance or equivalent capacitance of the strip into information reflecting the characteristics of the test strip prior to introduction of the sample allows useful characteristic information of the test strip to be obtained. As shown in fig. 1, in a preferred embodiment, the information obtained results in or is used in a subsequent action or step. In some embodiments, a subsequent action or step will produce or result in the display of an erroneous result or error message indicating that the test strip is not suitable for use with the meter or that some other error has occurred. In other embodiments, the subsequent action or step is an action or step of: the obtained or converted information is used for, or to modify the results obtained by, a subsequent measurement or analyte determination step.

Encoding information on test strips

Information can be encoded on the test strip by varying variables within the sample space that affect the equivalent and/or double layer capacitance of the strip as the sample covers the electrodes in the sample space. These variables include: controlling or changing the effective area of the electrodes within the sample space of the test strip, controlling or changing the structural material of the electrodes, electrode surface modification, controlling or changing the type or concentration of ions (e.g., type and amount of ions, such as those present in the reagent as salts), controlling or changing the type or concentration of the medium.

For example, in one embodiment, when information is encoded on a test strip, the effective electrode area can be changed or formed by increasing or decreasing the two-dimensional conductive surface area base region thereof (e.g., increasing/decreasing the length, width, or radius, etc.) that is in contact with the sample. Alternatively, or in combination with control over the two-dimensional surface area, the third conductive dimension of the electrode (e.g., where the electrode has a recessed or porous face in the third dimension that provides sample contact) may be altered/controlled by increasing/decreasing the thickness of the electrode. In other embodiments, the type and/or concentration of media or ions (e.g., salts) present in a reagent disposed within the sample space can be varied to encode information into the test strip, which in turn will vary the bilayer and/or equivalent capacitance of the strip, which allows for conversion and obtaining of information according to the methods described herein.

Determination of analytes, e.g. glucose

The method of the invention is preferably combined with a sub-routine involving the detection and/or determination of an analyte in a sample. The sub-routine of analyte detection and/or determination may occur before, during, or after the encoded information is obtained from the test strip. In some embodiments, the subroutine performed and/or the results of the test and/or the determination of the analyte are adjusted or modified depending on the type and content of the information obtained from the test strip. In other embodiments, the sub-routine of detecting and/or determining steps is stopped or not performed depending on the type and content of the information from the test strip. In still other embodiments, only an error message is displayed to the user depending on the characteristics obtained and encoded on the test strip.

The sub-routine for electrochemical detection and determination of an analyte, such as glucose, is typically accomplished by applying an electrical potential to an electrochemical cell containing a sample to which the presence/amount of glucose, an enzyme that oxidizes or reduces glucose, such as glucose oxidase, dehydrogenase, or reductase, and a redox mediator, or amounts thereof, are assessed. The reducing mediator is oxidized at one electrode and is held in electrochemical equilibrium by a reduction reaction at the other electrode to produce a measurable current. The measured current is related to the concentration of glucose in the sample, and various techniques are known for determining the glucose concentration in such systems. (see, e.g., U.S. Pat. Nos. 6284125, 5942102, 53522351, and 5243516, which are incorporated herein by reference.)

Other electrochemical techniques may also be used to perform the determination of glucose or other analytes in a sample. These include potentiometry, such as described in U.S. patent No. 6251260, which is incorporated by reference herein, or coulometry, such as described in U.S. patent No. 6299757, which is incorporated by reference herein.

In one embodiment, a method is provided for determining an analyte in a sample in contact with two electrodes within a sample space of an electrochemical test strip. The test strip has characteristic information encoded thereon prior to introduction of the sample. The method comprises the following steps:

(d) determining an analyte in a sample disposed in the sample space, and

(e) using the feature information converted in step (c) to modify the result of step (d).

Step (c) occurs after step (b), however step (d) may occur before or after step (b) or (c).

Apparatus of the invention

The method of the present invention can be used with any strip having at least two electrodes, so long as the meter device can receive the strip and provide the necessary voltage application and signal processing. Such meters also form an aspect of the present invention. Accordingly, the present invention provides a meter for receiving an electrochemical test strip having electrodes and providing a determination of an analyte in a sample applied to the electrochemical test strip when received in the meter, the meter comprising:

(b) a communication device for communicating the result to a user, an

(c) Circuitry and a processor for determining a double layer capacitance or equivalent capacitance on a test strip having two electrodes in a sample space containing a sample received in a meter; circuitry and a processor for converting the measured double layer capacitance or equivalent capacitance into information reflecting characteristics of the test strip prior to introduction of the sample; and circuitry and a processor for determining an analyte in a sample in the sample space of the test strip.

Fig. 7 shows an external view of a meter according to the invention. The meter has a housing 61 and a display 62. The housing 61 has an opening 63 into which a test strip is inserted for use. The meter may also have a button 64 for signaling the start of a measurement cycle, or may have internal mechanisms for detecting test strip insertion and/or sample application. Such mechanisms are known in the art, for example from U.S. patent nos. 5266179, 5320732, 5438271 and 6616819, which are incorporated herein by reference. In the meter of the present invention, buttons, displays such as LCD displays, RF, infrared or other wireless transmitters, wire connectors such as USB, parallel or series connections, constitute the means for receiving user input and communicating the results to the user, and may be used alone or in various combinations.

The meter of the present invention includes circuitry in the form of a processor, software and/or firmware or any other type of instructions or circuitry capable of performing the above-described method steps.

Examples

Information obtained from test strips-example 1

The electrochemical meter is configured to determine the double layer capacitance of a test strip disposed within the test strip interface. The control liquid sample is introduced to two different test strips, with different information encoded thereon due to having different effective electrode areas (e.g., strip 1-info 1/strip 2-info 2). It was determined that the control fluid filled the sample space and completely covered both electrodes within the sample space. The double layer capacitance of the two strips was measured and obtained as different values. These measurements are then transformed (e.g., by determining characteristic information in accordance with a lookup table with known double layer capacitance ranges) and the information encoded on the strip is determined as strip 1-info 1/strip 2-info 2.

Information obtained from test strips example 2

The electrochemical meter is configured to determine the equivalent capacitance of a test strip disposed within its test strip interface. The control liquid sample is introduced to two different test strips, with different information encoded thereon due to having different ionic salts present in the sample space (e.g., strip 1-potassium-info 1/strip 2-sodium-info 2). It was then determined that the control fluid filled the sample space and completely covered both electrodes within the sample space. The equivalent capacitance of the two bars was then measured and obtained as different values. These measurements are then converted (e.g., by matching the characteristic information with a lookup table having known equivalent capacitance ranges) and the information encoded on the bars is determined as bar 1-info 1/bar 2-info 2.

Claims

1. A method for obtaining characteristic information encoded on an electrochemical test strip having two electrodes disposed within a sample space, wherein the characteristic information is encoded on the test strip prior to introduction of a sample, the method comprising the steps of:

(a) introducing a sample into the sample space such that the sample is in contact with two electrodes within the sample space,

(b) determining a value representative of the double layer capacitance or equivalent capacitance of the test strip,

(c) converting the value determined in step (b) into information reflecting characteristics of the test strip prior to introduction of the sample, and

(d) performing an action based on the feature information converted in step (c),

one or both of the following:

(1) the characteristic information encoded on the strip is selected from calibration information, a region or country code, a product identification, a user identification, a test type, and a manufacturing date;

and/or

(2) The action performed in step (d) based on the characteristic information determined in step (c) is to modify the determination of the analyte in the sample arranged in the sample space of the test strip,

thereby obtaining information encoded on the electrochemical test strip.

2. The method of claim 1, further comprising the step of determining whether the sample completely covers the electrodes within the sample space, performed after step (a).

3. The method of claim 1 or 2, wherein step (b) is performed using the following steps:

(i) applying a potential difference between the electrodes of the test strip,

(ii) disconnecting the applied potential and optionally reapplying a second potential,

(iii) observing the current generated and determining from said observed current the double layer charge or discharge at said electrode, and

(iv) observing the voltage change after the applied potential is switched off, and

4. The method of claim 1 or 2, wherein step (b) is performed using the following steps:

(ii) (ii) measuring the current resulting from the application of the potential in step (i), and

(iii) (iii) determining the equivalent capacitance of the test strip from the current measured in step (ii), wherein the equivalent capacitance comprises both the double layer capacitance and the faraday capacitance of the test strip.

5. The method of claim 1 or 2, wherein step (b) is performed using the following steps:

(ii) converting the voltage caused by charging the test strip into an oscillating voltage having a period proportional to the resulting double layer capacitance, and

(iii) observing said oscillating voltage, an

6. The method of claim 1, wherein the characteristic information encoded on the strip is selected from the group consisting of: calibration information, area or country code, product identification, user identification, test type, and manufacturing date.

7. The method of claim 1, wherein the action performed in step (d) based on the characteristic information determined in step (c) is modifying the determination of an analyte in a sample disposed within the sample space of the test strip.

8. The method of claim 1, wherein the action performed in step (d) based on the characteristic information determined in step (c) is displaying an error message to a user regarding the test strip.

9. A method for determining an analyte in a sample in contact with two electrodes within a sample space of an electrochemical test strip, wherein the test strip has characteristic information encoded on the test strip prior to introduction of the sample, the method comprising the steps of:

(c) converting the values determined in step (b) into information reflecting characteristics of the test strip prior to introduction of the sample,

(d) determining an analyte in a sample disposed in the sample space, and

(e) the characteristic information converted in step (c) is used to modify the measurements made in step (d).

10. The method of claim 9, further comprising the step of determining whether the sample completely covers the electrodes within the sample space, performed after step (a).

11. The method of claim 9 or 10, wherein step (b) is performed using the following steps:

(i) applying a potential difference between the electrodes of the test strip,

12. The method of claim 9 or 10, wherein step (b) is performed using the following steps:

13. The method of claim 9 or 10, wherein step (b) is performed using the following steps:

(iii) observing said oscillating voltage, an

14. The method of claim 9, wherein the characteristic information encoded on the strip is selected from the group consisting of: calibration information, area or country code, product identification, user identification, test type, and manufacturing date.

15. The method of claim 1, wherein all steps (a) through (d) are performed for a single test strip.

16. The method of claim 15, wherein all of steps (a) through (d) are performed by the analyte meter while the test strip is received within the analyte meter.

17. The method of claim 16, wherein the action performed in step (d) based on the characteristic information determined in step (c) is to modify the determination of an analyte in a sample disposed within the sample space of the test strip.

18. The method of claim 16, wherein the action performed in step (d) based on the characteristic information determined in step (c) is to display error information about the test strip to the user.

19. A method for encoding characteristic information on a test strip having two electrodes disposed in a sample space and a bilayer when a sample covers the electrodes in the sample space, the method comprising performing a step of controlling or changing a variable in the sample space that affects a measurement representative of the capacitance of the bilayer when the sample covers the electrodes in the sample space, the step being selected from the group consisting of:

controlling or varying the effective area of the electrodes in the sample space;

controlling or changing the structural material of the electrodes in the sample space;

controlling or modifying the electrode surface in the sample space;

controlling or changing the type or concentration of ions within the sample space;

controlling or changing the type or concentration of the medium placed in the sample space,

wherein the steps are selected so that a measurement representative of the double layer capacitance as the sample covers the electrodes in the sample space can be converted into information reflective of the characteristics of the test strip,

thereby encoding characteristic information on the test strip.

20. The method of claim 19, wherein said characteristic information is information reflecting characteristics of said test strip prior to introduction of the sample.

21. The method of claim 19, wherein the characteristic information encoded on the strip is information selected from the group consisting of: calibration information, area or country code, product identification, user identification, test type, and manufacturing date.

22. The method of claim 19, wherein the method comprises the step of controlling or varying the effective area of an electrode in the sample space of the test strip, wherein the two-dimensional surface area of the electrode is controlled or varied.

23. The method of claim 22, wherein the three-dimensional surface area is controlled or varied.

24. The method of claim 19, wherein the method comprises the step of controlling or varying the effective area of the electrodes in the sample space of the test strip, wherein the three-dimensional effective electrode area is controlled or varied.

25. The method of claim 19, wherein the method comprises the step of controlling or varying the electrode area within the sample space, wherein the three-dimensional effective electrode area is controlled or varied.

26. The method of claim 19, wherein the method comprises the step of controlling or varying the type and/or concentration of ions present as salts in a reagent placed in the sample space.

27. The method of claim 19, wherein different characteristic information is encoded into the strip as the selected step is performed, such that the measured value representing the capacitance of the bilayer falls within different ranges of values.

28. The method of claim 19, wherein the ion is present in the reagent as a salt.