MXPA97010374A - Electroquim biosensor test strip - Google Patents

Abstract

The present invention discloses an electrochemical biosensor test strip (1), which has a minimum blood sample volume requirement of approximately 9 microliters. The test strip has working electrode (4) and opposite electrode (5) which are substantially of the same size and are made of the same electrically conductive material, placed on a first insulating substrate (2). The overlap of the electrodes is a second insulating substrate (3), which includes a cut portion (8) that forms a reagent well. The cut portion exposes a smaller area of the opposite electrode than the working electrode. A reagent for the analysis of an analyte substantially covers the exposed areas of the working and opposite electrodes in the reagent well. After the reagent well is fixed and fixed to the second insulating substrate, there is a diffusing mesh (13) which is impregnated with a surfactant. The small cut portion of 4 millimeters by 4.2 millimeters, the small mesh of 6 millimeters by 5.8 millimeters, and the small amount of reagent 4 microliters after drying, allow the test strip to analyze a sample of whole blood of approximately 9 microliters

Description

ELECTROCHEMICAL BIOSENSOR TEST STRIP Field of the Invention This invention relates in general to the determination of the concentration of analytes in fluids, and more specifically to an amperometric biosensor for use in such a determination.

Background of the Invention The biosensors are not new. Its use in the determination of concentrations of various analytes in fluids is also known. Nankai et al., WO 86/07632, published December 31, 1986, discloses a rich amperorne biosensor in which a fluid containing glucose is contacted with glucose oxidase and ether; potassium ianide. Glucose is oxidized and ferpyanide is reduced to ferrocyanide. (This reaction is catalyzed by glucose-oxidase). After two rr.ir. t'e, r is applied. Electrical potential and the current caused by the re-oxidation of ferrocyanide to ferricyanide is obtained. The current value obtained a few seconds after the REF: 26524 potential is applied, correlates the concentration of the glucose to the fluid. Because Nankai et al. Describes a method in which the reaction of glucose and ferricyanide can run to completion before the application of an electrical potential, this method is termed the "endpoint" method of the determination. amperometric Nankai et al. Describe a system in which glucose oxidase and potassium ferricyanide are maintained on a nonwoven nylon mesh. The mesh is placed so that it is brought into contact with a working electrode, an opposite electrode and a reference electrode. The total surface area of the opposite reference electrodes is that of the working electrode. Wogo an, EP 0 206 218, published on December 30, 1986, discloses ur. biosensor that has two electrodes, the electrodes of different electrically conductive materials being elaborated. For example, the anodc is md:. from an anode material, such as or plate, and the cathode is formed from a material, such as silver. The anode is coated with an enzyme. In a preferred embodiment, the coated electrode is covered with an elastomer that is permeable to glucose. Pottgen et al., WO 89/89/08713, published on September 21, 1989, describe the use of a two-electrode biosensor, wherein the electrodes are made of the same noble metal, but one of the electrodes (referred to as an electrode) of pseudoreference) is larger than the other (working) electrode. Recently, Pollmann and collaborators, US Patent No. 5,288,636, filed on February 22, 1994, discloses an eiectrochemical biosensor test strip that includes working electrodes and electrodes substantially contrary to the use and size and made from the same electrically conductive materials. The test strip of Poil ann et al. Includes a reagent well which will house a test sample of the whole human blood, from about 10 to about 70 microliters. However, below about 13 microliters, errors in anayite measurement, such as glucose, from a whole blood sample (low dose errors) may arise. In general, the low dose error is manifested as an underestimated measurement of the analyte, or no measurement of the analyte by the meter used in conjunction with the test strip. Low-dose errors are a particular problem for children and adults, who often have difficulty expressing a drop of blood of reasonable size for the test after pricking their finger with a lancet. Accordingly, it is highly desirable to design a test strip that requires a minimum volume of blood for testing an analyte, such as blood glucose.

Brief Description of the Invention The invention is an electrochemical biosensor test strip having a minimum volume blood sample requirement, smaller than the strips of the prior art, of similar construction. The present test strip of the invention has a smaller reagent well, and diffusion mesh smaller than similar strips of the prior art. In addition, the reagent well is positioned differently than in similar test strips of the prior art. The minimum requirement of the blood volume sample for the new strip is approximately 9 microliters.

The smaller sample volume requirement means that fewer dose errors per volume of low sample result when an analyte, such as glucose, is measured from a whole blood sample. This result is especially important for those people such as infants and the elderly, who have difficulty expressing a drop of reasonable blood size, by pricking their finger with a lancet. Also, with the strip of the present invention it is easier for the meter, which collects the current measurements and correlates those measurements at a concentration of analytes of a sample, discriminating the errors by low volume dosing of the sample. In addition, the smaller reagent well requires less reagent per biosensor strip, thereby increasing the volume of production for the mass production of the biosensor test strips. Further, when the diffusion mesh is attached to the test strip by an adhesive tape, the tape includes a hole that exposes the reagent well and the diffusion mesh, and also includes air vents on opposite sides of the hole. These air vents reduce the appearance of air bubbles trapped in the reagent well, when a sample is being tested. Air bubbles can cause errors in the test.

Brief Description of the Drawings Figure 1 is an exploded view of the biosensor test strip of the present invention.

Figure 2 is a top view of the biosensor test strip without the reagent, the diffusion mesh and the adhesive tape with air vents.

Figure 3 is a top view of the preferred biosensor test strip, fully constructed.

The figure is a cross-sectional view of the biosensor of figure 3, at the bottom of lines 21- Figure 5 illustrates the hypothetical calibration curves for different batches of biosensor test strips.

Description of the Preferred Modality The biosensor test strip of the present invention is similar to the preferred embodiment of the test strip described in Pollmann et al., US Patent No. 5,288,636 issued February 22, 1994, the disclosure of which is incorporated by reference in the present. However, the Pollmann strip and collaborators have such a construction that too many errors result from low dose when whole blood samples below about 13 microliters are tested for blood glucose. In the test strip of the present invention, well 9 (Fig. 4) of reagent has been reduced in size over the reagent well of Pollmann et al., And repositioned so that a smaller surface area of the opposing electrode is exposed. 5 that the working electrode 4, by the cutting portion 8, which forms the reagent well 9. (Figs 1-4) The mesh _1_3, which has a diffusion mesh, is also small on the mesh of Pollmann and collaborators (Figs 1, 3, 4). These changes in the architecture of the strip result in a test strip that can accurately measure an analyte, such as glucose, from a minimum sample of whole blood of approximately 9 microliters. With reference specifically to Figures 1 to 4, the currently preferred embodiment of the biosensor test strip of the invention is shown. The test strip 1_ comprises first and second electrically insulating layers 2 and 3, respectively.

Any useful insulation material will be appropriate.

Typically, plastics, such as vinyl polymers and polymers, which provide the electrical and structural properties are desired. Preferably, these layers are Melinex 329, 178 m (7 mil). The biosensor test strip shown in Figs. 1 to 4 is designed to be mass produced from relies of material, necessitating the selection of ur. material which is sufficiently flexible for roll processing, and at the same time rigid enough to give a useful stiffness to the finished double-strip test strip. Layers 2 and 3 can be of any useful thickness. In a preferred embodiment, layers 2 and 3 are approximately lrr. one thousand 'thick. The working electrode 4 and the counter electrode are preferably deposited on a reinforcement of insulating material 7, ai as a polyimide, to reduce the possibility of breakage of the electrode before it is fixed to the layer 2. The working electrode and the counter electrode 5 are substantially of the same size, and they are made from the same electrically conductive material. Examples of electrically conductive materials that can be used are palladium, platinum, gold, silver, carbon, titanium and copper. Noble metals are preferred because they provide a more constant reproducible electrode surface area. Palladium is particularly preferred, because this is one of the most difficult noble metals to oxidize, and because it is a relatively cheap noble metal. Silver is not preferred, as it is more easily oxidized by air than the other noble metals listed above. Preferably, electrodes 4 and 5 are approximately 0.1 micron thick and reinforcement 7 is approximately 25 microns thick (commercially available from Courtauld Performance Films in California and Scuthwall Technologies, Inc.). The electrodes 4 and 5 must be sufficiently separated so that the electrochemical events in one electrode do not interfere with the electrochemical events in the other electrode. The preferred distance between electrodes _4 and 5 is approximately 1.2 millimeters. In the preferred embodiment, the electrodes _4 and 5, fixed to the reinforcement 1_, are unwound from spools and coupled to the layer 2 by the use of hot melt adhesive (not shown). The electrodes 4_ and 5 also preferably extend from one end of the layer 2 towards the other end, in a parallel configuration. The insulating plate 3 is fixed on top of the layer 2 and the electrodes 4_ and 5 by the use of hot melt adhesive (not shown). Layer 3 includes cutting portion 8, which defines reactive well 9. The size and position of the cutting portions 8 are critical to the invention. The cutting portion 8 should be sufficiently small, and should be sufficiently placed such that in combination with the diffusion mesh, described below, a minimum total blood sample volume can be analyzed accurately by the test strip. of approximately 9 microliters. The preferred size of the cutting portion 8 is 4 millimeters by 4.2 millimeters. In the preferred embodiment, the 4 mm side of the cut portion 6 runs parallel to the longitudinal side of the test strip shown in Figures 1-4. Importantly, the cut portion 8 ^ is placed on the electrodes _ and 5, such that a smaller surface area of the counter electrode 5 is exposed than the working electrode 4. Preferably, the exposed surface area of the working electrode 4 is twice as large as the exposed surface area of the opposing electrode 5_. Surprisingly, the cut portion 8 in displacement, to expose a smaller surface area for the opposite electrode than the working electrode, does not adversely affect the measurement of an analyte from a sample that is measured. In this preferred embodiment, electrodes 4_ and 5 are 1.5 mm in width. The test strip of the biosensor 1 can be accompanied by a power source (not shown) in an electrical connection, with the working and opposite electrodes and a current meter (not shown) which is also an electrical connection with the electrodes of work and opposite. The biosensor reagent 1_1 (Figure 4) is placed on the pcb 9, so that it covers substantially all the exposed surfaces 10 and 20 of the working electrode 4 and 5, respectively. (Figures 2-4). An example of a reagent that can be used in the biosensor test strip of the present invention is a reagent for the measurement of glucose from a whole blood sample. A protocol for the preparation of a glucose reagent that uses the enzyme glucose oxidase and ferricyanide as the oxidized form of the redox mediator is as follows: Step 1 - Prepare 1 liter (in a volumetric flask) of a mixture of a striker / NATROSOL by adding 1.2000 grams (g) of NATROSOL-250 M to a 0.740 M aqueous potassium phosphate buffer (including 80.062 g of phosphate) monobasic potassium and 26,423 g of potassium dibasic phosphate) at pH 6.25. Allow NATROSOL to be agitated and swell for 3 hours.

Step 2- Prepare a mixture of AVICEL shake 14.0000 g of AVICEL RC-591 F and 504. ^ 750 g of water for 20 minutes.

Step 3- Prepare a mixture of TRITON by adding 0.50000 g of TRITON X-100 to 514.6000 g of mixture of amcrt equalizer / NATROSOL and stir for 15 minutes.

Step 4- While stirring, add the total TRITON mixture drop by drop with an addition funnel or burette to the total mixture of AVICEL. Once the addition is finished, stirring is continued overni Step 5- To the mixture resulting from Step 4, add, while stirring, 98.7750 g of potassium ferricyanide. (Add a little potassium ferricyanide at a time to allow the potassium ferricyanide to dissolve as it is added).

Step 6- Shake the mixture resulting from Step 5 for 20 minutes.

Step 7- Adjust the pH of the mixture resulting from Step 6 to 6.25 by the addition of potassium hydroxide.

Step 8 - To the mixture resulting from Step 7, add 9.1533 g of glucose oxidase (218.50 units of tetramethylbenzidine per milligram (mg) of Biozyme) and stir at least 20 minutes.

Step 9- To the mixture resulting from Step 8, add 20 g of potassium glutamate and stir at least 20 minutes.

Step 10 - Filter the resulting mixture from Step 9 through a 100 micron sieve bag to remove any AVICEL clusters. The filtrate is the resulting reagent composition (reagent 1_1), which is added to reagent well 9, and is then dried at about 50 ° C for about 3 minutes. In the preferred embodiment for the determination of glucose, 4 microliters of reagent prepared by the previously established protocol is added to well 9 formed by cut 8 ^. This amount of reagent 1_1 will substantially cover the surface areas 1_0 and 2_0 of electrodes 4_ and 5 (Figure 2) and will also contain a sufficient amount of ferricyanide, and a sufficient amount of glycine-oxidase enzyme) to catalyze the oxidation of glucose. from a sample of human whole blood) and the reduction of the ferricyanure to completion, as stated herein, within about 20 seconds. (Before adding reagent to well 9, it is preferable to treat pozc 9 with a 600 watt corona arc, at a separation of c.35 x 10"cm (1 / 40,000 inch) on a processing line that travels to 4 meters per minute, to make the well 9 more hydrophilic, which allows the reagent to diffuse more evenly in the well.) Another glucose reagent that can be formulated includes 300 millimolar potassium ferricyanide, potassium phosphate buffer 250 millimolar, 14 grams of microcrystalline cellulose (AVICEL RC-591 F) per liter of reagent, 0.6 grams of hydroxyethylcellulose (NATROSOL-250 M) per liter of reagent, 0.5 grams of Triton X-100 as surfactant per liter of reagent, succinate of sodium 37 millimolar, and 1.5 million units of tetramethylbenzidine glucose oxidase per liter of reagent.Sodium hydroxide (normal solution 6) is used to titrate this reagent to a pH of 6.6. same protocol described above, but the amounts of the components must be adjusted, and the components substituted (sodium succinate by potassium guttate and sodium hydroxide by potassium hydroxide) to achieve the concentrations of the components set forth above. Drying this reagent in reagent well 9 typically results in a loss of enzyme activity of about 30-35%. After the drying of reagent 1_1, a diffusing mesh 1_3, which has been impregnated with a surfactant, is placed on the cut portion 8 and is fixed to the second electrical insulator _3. The diffusion mesh 1_3_ is preferably a polyester monofilament mesh of ZBF (Zurich Bolting Cloth Mfg. Co. Ltd., Rüschlikon, Switzerland). The diffusing mesh is preferably submerged in a solution of 0.8% dioctylsodium sulfosuccinate (weight: volume) (DONS) in a 50:50 methanol: water solution (volume: volume) and then dried. The diffuser screen 1_3 must be sufficiently small, such that in combination with the size of the cut portion 8i and the placement of the cut portion 8, the biosensor strip will accurately measure the analyte from a sample of whole blood of approximately 9 microliters. The preferable dimensions of diffuser mesh 1_3 are 6 mm x 5.8 m. In the most preferred biosensing strip, the 6 mm side of the mesh is parallel to the longitudinal side of the strip shown in Figures 1-4. Preferably, the diffusing mesh 1_3 is fixed to the adhesive tape 1_4, which includes the hole 1_5 (Figures 1, 3, 4). The adhesive tape 14 is preferably made of polyester with an adhesive reinforcement. (Available from Tapemark, Medical Products Division, 223 E. Marie Ave., Saint Paul, Minnesota 55118. * Adhesive tape 14 is preferably pigmented brown and hole 15 provides a target area for the application of a sample to be analyzed by the biosensor The orifice L5 exposes at least a portion of the diffuser screen 1_3 and the cut portion 8, and preferably substantially exposes the entire cut portion 8. The tape 1_4 preferably includes the slits 1_6, as shown in Figures 1 and 3, located on opposite sides of the hole _15. (Two slits 1_6 are shown in Figures 1 and 3, but a slit may suffice.) The slits or channels 1_6 constitute air vents, which reduce the appearance of air bubbles. air entrapped in the reagent well, after the addition of a sample such as whole blood to the reagent well, reducing the appearance of air bubbles trapped in the well or 9 of reagent, results in minor test errors. After the drying of the reagent and the fixing of the diffusing mesh, the biosensors formed er. roll are separated by puncture by punch to form discrete biosensors, which are used in conjunction with 1) a power source in electrical connection with the working and opposite electrodes, and capable of supplying an electrical potential difference between the working electrode and the opposite electrode sufficient to cause limited electrooxidation by diffusion of the reduced form of the redox mediator on the surface of the working electrode, and 2) a meter in electrical connection with the working electrode and the opposite electrode, and capable of measuring the limited diffusion current produced by the oxidation of the reduced form of the redox mediator, when the previously established electric potential difference is applied. The meter described above will normally be adapted to apply an algorithm (discussed below) to the current measurement, by which a concentration of the analyte is provided, and displayed visually. Improvements in such energy source, meter, and biosensor system are the subject of commonly assigned United States Patent No. 4,963,814, issued October 16, 1990; American Patent Ne. 4,999,632, issued March 12, 1991; U.S. Patent No. 4,999,582, issued March 12, 1991; U.S. Patent No. 5,243,516, issued September 7, 1993; American Patent Ne. 5,352,351, issued October 4, 1994; U.S. Patent No. 5,366,609, issued November 22, 1994; White et al., US Patent Application No. ,405,511, filed April 11, 1995 and White et al., U.S. Patent Application No. 5,438,271, filed August 1, 1995, the descriptions of which are incorporated by reference 5 herein.

For ease and electrical connection of the power source and the meter, the additional cut portion 1_2 (Figures 1 to 4), the exposure 0 portions of the working electrode and counter, are preferably provided in the biosensor device. The biosensor device described above can be used to determine the concentration of an analyte in a fluid sample by performing the following steps: a) contacting a sample of fluid, such as whole blood, with a reagent (described above), which substantially covers the "" - surface areas 1_0 and 2_0 of the working electrodes and counter 4_ and 5, respectively; B) allowing the reaction between the analyte and the oxidized form of the redox mediator, to the termination, as defined herein; c) subsequently applying a potential difference between the electrodes, sufficient to cause the electrooxidation limited by diffusion of the reduced form of the redox mediator at the surface of the working electrode; d) after this, the resulting limited current by diffusion is measured; and e) the correlation of the measurements of the current to the concentration of the analyte in the fluid. (The termination of the reaction is defined as the sufficient reaction between the analyte and the oxidized form of the redox mediator, to correlate the concentration of the analyte to the diffusion-limited current, generated by the oxidation of the reduced form of the redox mediator in the surface of the working electrode). Many fluids containing analytes can be analyzed. For example, analytes in human body fluids such as whole blood, blood serum, urine and cerebrospinal fluid can also be measured. Also, the analytes found in the fermentation products and environmental substances, which potentially contain environmental contaminants, can also be measured.

When measuring analytes found in human body fluids, especially whole blood, the difference in potential applied between the electrodes is preferably no greater than about 500 millivolts. When a potential difference is applied above about 500 millivolts between the electrodes, oxidation on the surface of the working electrode (for palladium) and some blood components may become intolerable, thereby preventing a correlation correct and accurate current to the concentration of the analyte. For a glucose test on a whole blood sample, where the oxidized form of the redox mediator is ferricyanide, a potential difference from about 150 millivolts to about 500 millivolts between the electrodes can be applied to achieve electrooxidation limited by diffusion of the reduced form of mediator redcx on the surface of the working electrode. Preferably, approximately 300 millivolts of potential difference between the electrodes is applied. The current generated from oxidation to the reduced form of the redox mediator, it can be measured at any time from about 0.5 seconds to about 30 seconds after the potential difference between the electrodes is applied. At less than about 0.5 seconds, it is difficult to measure the current limited by diffusion, 5 due to the charging current. After approximately 30 seconds, the convection becomes significant, which interferes with the measurement of a diffusion-limited current. The current mediated during the test of a The analyte from a fluid sample can be correlated to the concentration of the analyte in the sample by applying an algorithm to the current meter. The algorithm can be a simple one, as illustrated by the following example. 15 [Anaíito] = Ci. > + d where [Analitc] represents the concentration of the analyte in the sample (see Figure 5), i - _. is the current l (in microamperes: measured at 7.5 seconds after the application of the applied potential difference between the electrodes, C is the slope of line 22 (Figure 5, and d is the ordinate at the origin (Figure 5).

By measuring with known concentrations of analyte, the calibration curve 2_2 can be constructed (Figure 5). This calibration will be stored in the meter's Read Only Memory (ROM) key, and will be applicable to a particular batch of biosensor test strips. Lines 2_4 and 2_6 in Figure 5 represent other hypothetical calibration curves for two different batches of biosensor test strips. The calibration for these biosensing lots could generate slightly different values for C and d in the previous algorithm. A glucose analysis from a human whole blood sample, 20 μl of whole blood is preferably added to the aforementioned glucose reagent. The reaction of glucose and ferricyanide is allowed until completion, with which gluconic acid and ferrocyanide are formed. This reaction usually requires a short time, preferably less than about 20 seconds, until termination. Approximately twenty seconds after the addition of the whole blood sample, a potential difference of approximately 300 millivolts is applied between the electrodes, whereby the ferrocyanide is oxidized to ferricyanide on the surface of the working electrode. Current measurements are made at 0.5 second intervals from 1 second to 7.5 seconds after the potential difference between the electrodes is applied. These current measurements are correlated to the concentration of glucose in the blood sample. In this example of glucose measurement from a blood sample, the current measurements are made at different times (from 1 second to 7.5 seconds after the application of the potential difference), instead of at a single fixed time (as described above), and the resulting algorithm is more complex and can be represented by the following equation: [Glucose] = C i + i + C, i, + ... C "i" + d, where i is the current measured at the first measurement time (1 second after the application of the potential difference of 300 millivolts), i ... is the current measured at the second measurement time, 1.5 seconds after the application of the potential difference of 300 ml and 1 tios), i. is the current measured at the third measurement time (2 seconds after the application of the potential difference of 300 mi 11 volts i, i is the measured current at the nth measurement time (in this example, at 14 measurement time or 7.5 seconds after the application of the potential difference of 300 millivolts), C :, C., C, and C, are coefficients derived from a multivariate regression analysis technique, such as the Analysis of Principal Components or Partial Least Squares, and d is the ordinate at the origin of the regression (in units of glucose concentration). (A modification of this procedure can be used in the event that the calibration curves illustrated in Figure 5 have considerable curvature.) Alternatively, the concentration of glucose in the sample that is measured can be determined by integrating the curve generated by the current trace, and, versus the measurement time on some n time interval (for example, from 1 second to 7.5 seconds after the application of the potential difference of 300 millivolts), with which the total load transferred during the measurement period is obtained. The total load transferred is directly proportional to the concentration of glucose in the sample that is measured. In addition, the glucose concentration measurement can be corrected for differences between ambient temperature, the time of the current measurement and the ambient temperature at the time the calibration was performed. For example, if the calibration curve for the measurement of glucose was constructed at an ambient temperature of 23 ° C, the measurement of glucose is corrected by using the following equation: [Glucose] ....,! -,., = [Glucose] ^ ,,,, x (1-K (T-23 ° C)), where T is the ambient temperature (in ° C) at the time of the measurement of the sample and K is a constant derived from the following regression equation: Y = K (T-23), where Y = [Glucose]. ,, at 23 ° C - [Glucose] ...:,; , at T ° C [Glucose]. ,. ,. to T ° C Cor. In order to calculate the value of K, each of a plurality of glucose concentrations is measured by the meter at different temperatures, T, and at 3 ° C (the base case). Next, a linear r ^ ression of Y on T-23 is performed. The value of K is the slope of this rear sirn. The glucose concentration of a sample can be measured accurately and accurately by the method of the present invention, using the biosensor of the present invention. In addition, when a complete human blood sample is measured, the error due to the hematocrit effect is negligible in the hematocrit range of 30-55 o. Other examples of enzymes and redox mediators (oxidized form) that can be used in the measurement of particular analytes by the present invention are listed below in Table 1.

Table 1 In some of the examples shown in Table 1, at least one additional enzyme is used as a reaction catalyst. Also, some of the examples shown in Table 1 may use an additional mediator, which facilitates the transfer of electrons to the oxidized form of the redox mediator. The additional mediator can be provided to the reagent in lesser quantity than the oxidized form of the redox mediator. When compared to the preferred embodiment of the closest-like biosensor test strip described in Pollmann et al., The biosensor of the present invention has the following distinguishing characteristics: 1. reagent well 9 is 30 ° or more little; 2. when the working and reversing electrodes are substantially of the same size, the exposed surface area of the opposite electrode in the reagent well is less than the exposed surface area of the working electrode in the reagent well; 3. a small amount of reagent is necessary in the reagent well (4 microliters of reagent versus 6 microliters of reagent in the preferred embodiment of Pollmann et al.); 4. a smaller diffuser mesh is needed; and 5. air vents are included on opposite sides of the reagent well. A smaller sample volume requirement to properly dose the test strip means that fewer dosing errors will result. This result is especially important for those people, such as children and the elderly in whom they have difficulty obtaining a drop of blood of reasonable size after pricking their finger with a lancet. The present strip of the invention makes it easier for a current meter to discriminate errors by low dosing of sample volume. Also using less reagent per sensor increases the production volume for mass produced sensors. In addition, the provision of air vents near the reagent well reduces the appearance of air bubbles trapped in the reagent well, which results in minor test errors. The present invention has been described in the teachings and drawings above, with sufficient clarity and conciseness to enable one skilled in the art to make and use the invention, to know the best mode for carrying out the invention, and to distinguish it from other inventions. Many obvious inventions and adaptations of the invention will come quickly to mind, and it is intended that they be contained within the scope of the invention as claimed herein.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, property is claimed as contained in the following:

Claims (10)

1. A device for detecting or measuring the concentration of an analyte, characterized in that it comprises: a first electrical insulator; two electrodes only, said electrodes consist of the working electrode and the counter electrode of substantially the same size, made of the same electrically conductive materials, and being supported on the first electrical insulator; a second electrical insulator, which overlaps the first electrice insulator and the electrodes, and which includes a cut portion that exposes a smaller surface area of the opposite electrode than the locking electrode; a reactive to detect or measure the concentration of the electrode;, substantially reactive the exposed surfaces of the electrode in the cut Terce; and a mesh, impregnated with a surfactant, which overlaps the portion cut and fixed to the second electrical isolator, where the cut portion and the diffusing mesh are of sufficient size and the reagent is in sufficient quantity to receive a minimum sample of whole blood of approximately 9 microliters to analyze the analyte.

2. The device according to claim 1, characterized in that the diffusing mesh is fixed to the second substrate with tape, having an adhesive on one side and a hole that exposes at least a portion of the diffusing mesh and the cut portion, and wherein the The tape also includes at least one slit near the hole, thereby providing at least one air vent.

3. The device according to claim 1, further characterized in that it comprises a current meter in electrical connection with the working electrodes v opposite.

4. The device according to claim 2, characterized in that the tape includes slits on opposite sides of the hole, whereby two air vents are provided.

5. The device according to claim 2, characterized in that the cut portion is 4 millimeters by 4.2 millimeters.

6. The device according to claim 5, characterized in that the diffusing mesh is 6 millimeters by 5.8 millimeters.

7. The device according to claim 6, characterized in that the amount of reagent is 4 microliters before drying.

8. The device according to claim 7, characterized in that the diffusing mesh is impregnated with sui dioctylsodium phosuccinate.

9. The device according to claim 8, characterized in that the hole in the tape substantially exposes the entire cut portion.

10. The device according to claim 9, further characterized in that it comprises a current meter in electrical connection with the working and opposite electrodes.