REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application Serial No. 61/240,619, filed September 8, 2009, and entitled "Electrochemical Test Sensor," which is incorporated herein in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates generally to test sensors, and more specifically to an electrochemical test sensor that is adapted to determine the concentration of an analyte.

BACKGROUND

[0003] Medical conditions such as diabetes require a person afflicted with the condition to regularly self-monitor that person's blood-glucose concentration level. The purpose of monitoring the blood glucose concentration level is to determine the person's blood glucose concentration level and then to take corrective action, based upon whether the level is too high or too low, to bring the level back within a normal range. The failure to take corrective action may have serious medical implications for that person.

[0004] One method of monitoring a person's blood glucose level is with a portable testing device. The portable nature of these devices enables users to conveniently test their blood glucose levels at different locations. One type of device utilizes an electrochemical test sensor to harvest and analyze the blood sample. The test sensor typically includes a capillary channel to receive the blood sample and a plurality of electrodes. Some electrochemical test sensor devices have larger capillary channels than are optimally desired. The bigger the capillary channel, the more blood from a person is required to fill the channel. Because drawing blood from a person is unpleasant, it would also be desirable to reduce the size of the capillary channel to require less blood. However, there must be sufficient blood to cover and activate the plurality of electrodes used in an electrochemical test sensor. Thus, there exists a need for an electrochemical test sensor with a smaller capillary channel without sacrificing the accuracy of the analyte concentration determination.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 A is a perspective view of an electrochemical test sensor according to an embodiment.

[0006] Figure IB is a perspective view of an electrochemical test sensor according to another embodiment. [0007] Figure 2A is a perspective view of an electrode assembly according to an embodiment.

[0008] Figure 2B is a top view of the electrode assembly of Figure 2A.

[0009] Figure 2C is a bottom view of the electrode assembly of Figure 2 A.

[0010] Figure 2D is a front view of electrochemical test sensor of Figure 1A.

[0011] Figure 2E is a top view of the reaction channel of an electrochemical test sensor of

Figure 1A.

[0012] Figure 3A is a perspective view of an electrode assembly according to another embodiment.

[0013] Figure 3B is a top view of an electrochemical test sensor according to an embodiment.

[0014] Figure 3C is a bottom view of an electrochemical test sensor according to an embodiment.

[0015] Figure 4 is a top view of an electrochemical test sensor according to an embodiment.

[0016] Figure 5 is a perspective view of an electrochemical test sensor with a lancet mechanism according to an embodiment.

[0017] Figure 6 is a perspective view of an electrochemical test sensor with an integrated lancet mechanism according to an embodiment.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

[0018] The present invention is directed to an electrochemical test sensor that is adapted to be placed into a meter or an instrument and assist in determining an analyte concentration in a body fluid sample. The present electrochemical sensor assists in reducing the volume of the fluid sample needed to properly determine the analyte concentration. The body fluid sample may be collected with a lancing device with which the electrochemical sensor is coupled thereto or integrated therewith.

[0019] Examples of the types of analytes that may be collected include glucose, lipid profiles (e.g., cholesterol, triglycerides, LDL and HDL), microalbumin, hemoglobin Al _c , fructose, lactate, or bilirubin. It is contemplated that other analyte concentrations may also be determined. It is also contemplated that more than one analyte may be determined. The analytes may be in, for example, a whole blood sample, a blood serum sample, a blood plasma sample, other body fluids like ISF (interstitial fluid) and urine, and non-body fluids. As used within this application, the term "concentration" refers to an analyte concentration, activity (e.g., enzymes and electrolytes), titers (e.g., antibodies), or any other measure concentration used to measure the desired analyte.

[0020] Figure 1A illustrates a perspective view of an electrochemical test sensor in accordance with an embodiment. Figure IB is a perspective view of an electrochemical test sensor according to another embodiment. As shown in Figure 1A, an electrochemical test sensor 100 includes a housing 102 having a meter-contact end 104, a front opening end 106, and an electrode assembly 108 positioned within the housing 102. As shown in Figures 1A and IB, the housing 102 is generally cylindrical in shape, whereby at least a portion of the housing 102 (desirably at the front opening end) may have a cross-sectional shape such as circular (Figure 1A). The housing may have a rectangular cross-sectional shape such as shown with housing 102' (Figure IB). It is contemplated that the housing may have other polygonal or non-polygonal cross-sectional shapes.

[0021] The electrode assembly 108 is shown in Figures 1A and IB within the interior of the housing 102, whereby at least a portion of the assembly 108 is configured to separate the interior of the housing into distinct capillary channels 122, 124 (see also Figure 2D). A reaction channel 109 (FIG. 1A) is shown as the volume within the housing 102 that surrounds the tip (described below) of the electrode assembly's front end 101 (Figure 2A). In an embodiment, the front end 101 of the electrode assembly 108 is located inward a set distance from the front opening end 106 such that the reaction channel 109 occupies the space between the front opening end 106 and the front end 101 of the electrode assembly 108. It is contemplated that the front end of the electrode assembly may be positioned differently with respect to the front opening end of the reaction channel. For example, a front end of the electrode assembly may be flush with the front opening end of the housing. In another example, a front end of the electrode assembly may extend outwardly from the front opening end and, thus, would be exposed outside the housing. In a further example, the length of the housing 102 may be smaller than depicted in FIG. la as long the length of the housing is sufficient to allow the sample to travel from the sensor tip. In operation, the user's fluid sample is received within the reaction channel 109 wherein analyte in the fluid sample reacts with the electrodes of the electrode assembly and is then used to determine analyte concentration in the sample. [0022] Figure 2 A illustrates a perspective view of the electrode assembly in accordance with an embodiment. Figures 2B and 2C show respective top and bottom views of the electrode assembly shown in Figure 2A. As shown in Figure 2A, the electrode assembly 108 includes a substrate 110 having a first surface 112 and a second surface 114, a working electrode 116 and a counter electrode 118. The working electrode 116 is disposed on the first surface 112 and the counter electrode 118 is disposed on the second surface 114. The working electrode 116 and counter electrode 118 are thus disposed on opposing surfaces of the substrate and are effectively in a back-to-back configuration with respect to the substrate 110. This is further shown in Figure 2B in which the working electrode 116 is shown exposed when viewing the assembly 108 from one side, whereas the counter electrode 1 18 is shown exposed when the electrode assembly 108 is flipped onto the opposing side (see Figure 2C).

[0023] As shown in Figure 2C, the electrode assembly 108 desirably has a uniform width dimension W along a substantial portion of its length, however this is not necessary. In this embodiment, the width dimension W is substantially equal to the inside diameter or width dimension of the housing 102. By having such a width dimension, the electrode assembly 108 affectively separates the interior of the housing into a first capillary channel 122 and a second capillary channel 124 in Figure 2D, except desirably proximal to the tip. The back-to- back configuration of the working and counter electrodes 116, 118 is advantageous in this embodiment, because the electrodes 116, 118 may effectively operate while minimizing the amount of required capillary space to perform the analysis on the fluid sample. This, in turn, allows the electrode assembly 108 to effectively perform the analysis on a smaller amount of fluid sample.

[0024] As shown in Figures 2B and 2C, the electrode assembly 108 has two sides 113a, 113b and also two tapering sides 111a, 111b between points 117a, 117b and the front end 101. This entire front portion of the electrode assembly 108 between points 117a, 117b and the front end 101 is generally referred to as the tip of the electrode assembly 108. As shown in Figures 2A-2C, the front end 101 is a relatively straight edge, although this is not necessary. As stated above, the reaction channel 109 is the volume within the housing 102 that surrounds the tip of the electrode assembly 108. The sides 111a, 111b of the electrode assembly 108 desirably abut in inside surface of the tube 102, as shown in Figure 2D. This configuration creates a working area that links or allows fluid communication between the two capillary channels 122, 124 near the front opening 106 of the housing as shown in Figure 2E. This configuration assists in increasing capillary action of the fluid as it is received by the sensor.

[0025] It is contemplated that the front end may alternatively be a pointed end, a rounded edge or other shapes. It should be noted that it is not required that both sides 111a, 11 lb of the electrode assembly 108 taper toward one another. It is contemplated that only one side may be straight while the other opposing side is configured at an angle. In another embodiment, the tip may have other appropriate shapes such as semicircular, bow-tie, and the like that desirably increase capillary action of the fluid received between the two channels.

[0026] The working electrode 116 and the counter electrode 118 assist in electrochemically determining the analyte concentration of the received fluid sample. In one embodiment, the working electrode 116 and the counter electrode 118 may be made from conductive material including, but not limited to, carbon, gold, platinum, ruthenium, rhodium, palladium or combinations thereof. The electrodes typically connect with the meter contact area using an electrode pattern. The electrode pattern may include test-sensor contact and conductive leads. The working electrode area is less than 1.0 mm ² and desirably about 0.5 or 0.6 mm ² or even 0.3mm ² . The electrodes may be formed by techniques such as screen printing, sputtering, laser ablation, combinations thereof or other manufacturing methods.

[0027] The substrate may be made of polymeric materials including but not limited to polyethylene terephthalate (PET), polysterene, polyimide, polycarbonate and combinations thereof. The housing 102 may be made of polymeric materials such as polyvinyl chloride (PVC) and the like. The housing may be made of metallic materials and alloys such as, for example, nickel-titanium alloy or nitinol. Nitinol may be desirable because of its shape memory and superelasticity. The interior of the housing may include a hydrophilic coating to increase the fill rate of the liquid sample into the capillary channels.

[0028] A reagent is desirably disposed on the working electrode 116 in Figure 2B. A reagent may additionally or alternatively be disposed on the counter electrode 118 in Figure 2C. In particular, the reagent is located along a portion of or the entire surfaces of one or more of the electrodes 116, 118. The reagent converts an analyte (e.g., glucose) in the fluid test sample, stoichiometrically into a chemical species that is electrochemically measurable, in terms of electrical current it produces, by the components of the working electrode 116 and the counter electrode 118. The reagent typically includes an enzyme and an electron acceptor. The enzyme reacts with the analyte to produce mobile electrons on the working and counter electrodes 116, 118. For example, the reagent layer may include glucose oxidase, glucose dehydrogenase (GDH), and/or a surfactant if the analyte to be determined is glucose. The enzyme in the reagent layer may be combined with a hydrophilic polymer such as poly(ethylene oxide) or other polymers such as polyethylene oxide (PEO), hydroxyethyl cellulose (HEC), carboxymethylcellulose (CMC) and polyvinyl acetate (PVA). The electron acceptor (e.g., ferricyanide salt) carries the mobile electrons to the surface of the working electrode 116. Amperometry detection methods and gated amperometry detection methods may be applied to analyze the sample. Other diffusional electron mediators, such as ferrocene derivatives, conducting organic salts (tetrathiafulvalene-tetracyanoquinodimethane, TTF-TCNQ), hexamineruthenium (III) chloride, quinone compounds, transition-metal complexes, and phenothiazine and phenoxazine compounds, are particularly useful to electrically contact glucose oxidase.

[0029] The electrode assembly 108 desirably includes underfill electrodes 120, which are located on one or both surfaces of the substrate 110. It is contemplated that an electrochemical sensor may include other electrodes such as an underfill electrode, hematocrit-detection electrode. As shown in Figures 2A-2C, the electrode assembly 108 includes a pair of underfill electrodes 120 that are located on the first and/or second substrate surfaces 112, 114, whereby the pair of underfill electrodes 120 are adjacent located between the sides 113a, 113b of the assembly 108 and the center sections 115a, 115b of the respective electrodes 116, 1 18.

[0030] In particular, as shown in Figure 2B, underfill electrode 120a is located between the side 113a and the center section 115a, whereas another underfill electrode 120b is located between side 113b and the center section 115a. Regarding the opposing side, as shown in Figure 2C, underfill electrode 121a is located between the side 113b and the center section 115b, whereas the other underfill electrode 121b is located between side 113a and the center section 115a. It is contemplated in another embodiment that only one underfill electrode 120, instead of a pair, be located on either or both surfaces of the substrate.

[0031] Figures 3A-3C illustrate an alternative electrode assembly 200 in accordance with another embodiment. The assembly 200 includes a substrate 201 having a first side 201 A and a second side 20 IB. A working electrode 202 is shown disposed on the first side 201 A and a counter electrode 204 are disposed on the opposing second side 20 IB. Additionally, a first underfill electrode 206 is disposed adjacent to the working electrode 202 on the first side 201 A. A second underfill electrode 208 is disposed adjacent to the counter electrode 204 on the second side 20 IB of the substrate 201.

[0032] As shown in the perspective view of Figure 3 A, the working electrode 202 having a generally L-shaped configuration, whereby the underfill electrode 206 is located adjacent to the working electrode 202 and occupies the remainder of the first side 201 A of the substrate. In addition, the counter electrode 204 on the second side 20 IB of the substrate has a generally L-shaped configuration along with the corresponding underfill electrode 208.

[0033] In particular, the underfill electrodes 206, 208 on the opposing surfaces of the substrate 201 are inverted with respect to one another. As shown in Figure 3 A, the L-shaped working electrode 202 is located on the right side of the electrode assembly 200 (as viewed from the arrow 99), whereas the L-shaped counter electrode 204 is located on the left side of the electrode assembly 200 (as viewed from the arrow 99).

[0034] Figures 3B and 3C illustrate the opposing surfaces of the electrode assembly 200 within a housing 210. As shown in Figures 3B and 3C, the underfill electrodes 206 (Figure 3B) and 208 (Figure 3C) appear on the same side laterally with respect to the corresponding electrode 202, 204. It is contemplated, however, that the underfill electrodes may mirror one another and are not inverted such that they are laterally located in the same area on opposing sides of the substrate.

[0035] Figure 4 illustrates an electrochemical test sensor in accordance with another embodiment. As shown in Figure 4, the electrochemical test sensor 300 includes a housing 302 with a front opening end 312. An electrode assembly 304 is positioned within the housing 302 and includes a tip 306 proximal to the front opening end 312 of the housing 302.

[0036] As shown in Figure 4, an underfill electrode 308 is located approximately centrally along the surface of the electrode assembly 304. The underfill electrode 308 includes a main body 312 and an extension leg 310 which extends toward the tip 306 of the electrode 304. The extension leg 310 desirably has a width dimension smaller than the main body 312 of the underfill electrode 308. It is contemplated that the other side of the electrode assembly 304 may have a similar configuration to that shown in Figure 4, although it is not necessary. It should be noted that the above configurations of the underfill electrodes on the electrode assembly are examples and other designs, orientations, layouts and positions are contemplated. [0037] It is contemplated that the sensors may be used to detect more than one analyte using modifications of the embodiments discussed above. In such an embodiment, an additional working electrode would be added to the sensor on an opposing side of the existing working electrode. The reagents to be used on the respective working electrode would be appropriately selected to assist in determining the concentrations of the desired analytes. Thus, two different analyte concentrations may be determined using one sample. In this embodiment, the counter electrode may be used in conjunction with each of the working electrodes. In another embodiment, a separate counter electrode may be formed on an opposing side of the existing counter electrode.

[0038] Figure 5 illustrates a perspective view of the above described sensor configured for use with a lancet mechanism in accordance with an embodiment. As shown in Figure 5, a sensor-lancet assembly 400 includes the sensor 402 and a lancet mechanism 404 removably coupled to the sensor 402. In particular, the sensor 402 includes the sensor assembly 406 positioned within the housing 408, in which an electrode tip 410 of the sensor assembly 406 is positioned within a lancet interface 412 coupled to the end of the housing 408.

[0039] The lancet mechanism 404 includes a lancet adapter 414 and a lancet needle 416 extending from the lancet adapter 414. The lancet adapter 414 holds the lancet needle in place and also interfaces with the lancet interface 412 of the sensor 402. The lancet needle 416 punctures the user's skin to obtain a fluid sample that will be collected. Although not required, the adapter and interfaces may be configured to allow selective removal and replacement of the lancet mechanism from the sensor.

[0040] The lancet adapter 414 is desirably configured to be in communication with the lancet needle 416 and the tip 410 of the sensor 402 such that the fluid sample travels from the lancet needle 416 through the lancet adapter 414 to be received at the sensor tip 410. It is desirable that the electrode tip 410 is precisely positioned within the interface 412 to ensure that it receives a predetermined sample volume. It is also contemplated that the sensor may alternatively be incorporated inside the lancet needle in an embodiment. Although one particular type of electrode sensor 400 is shown in Figure 5, it should be noted that any of the above described sensor embodiments may be used with the lancet device described herein.

[0041] Figure 6 illustrates a schematic of an integrated sensor and lancet mechanism in accordance with another embodiment. As shown in Figure 6, integrated sensor/lancet 500 has a housing 502 and a sensor 504 located within the housing 502. The housing 502 forms an opening 507. The sensor 504 includes a tapered tip 506 that extends out from the opening 507 and forms a sharp end 508. Thus, the portion of the sensor 500 exposed outside of the housing 502 functions as a lancet needle 510. As shown in Figure 6, the lancet needle 510 desirably includes a sample transport channel 512 that terminates at an aperture at (or proximal to) the sharp end 508 of the needle 510. The transport channel 512 is configured to be in communication with the tapered tip 506 of the sensor 504 and is desirably treated with a hydrophilic material such that the sample automatically travels upward from the incision site directly to the sensor 504 without the need for any additional components or attachments.

[0042] In operation, the integrated sensor/lancet 500 extends toward the user's skin, whereby the needle 510 makes a small incision in the skin. The fluid sample desirably flows upward via the channel 512 to the tapered area 506. It is desirable that the tapered area 506 is precisely positioned within the housing 502 to ensure that it receives a predetermined sample volume. Although one particular type of electrode sensor 504 is shown in Figure 6, it should be noted that any of the above described sensor embodiments may be used with the lancet assembly described herein.

[0043] In another embodiment, the integrated sensor/lancet 500 of Figure 6 may be modified for use in a continuous glucose-monitoring (CGM) system. In such an embodiment, the integrated sensor/lancet may be simplified by eliminating unnecessary items such as the housing 502, resulting in a system without a sample transport channel 512 being formed. In a continuous glucose monitoring embodiment, the underfill detection electrodes are not necessary. The continuous glucose-monitoring system includes a working electrode on one side and a counter electrode on the opposing side as discussed above. The working electrode in this embodiment may be formed of, for example, platinum or gold and the counter electrode may be formed of, for example, silver/silver chloride. It is contemplated that other materials may be used in forming the electrodes to be used in the glucose- monitoring system. A tapered tip in the continuous glucose-monitoring system would extend out to form a sharp end that assists in inserting the modified integrated sensor/lancet into the skin.

[0044] In one or more of the above embodiments, the working electrode desirably has a surface area of approximately 0.6 mm ² or less. It is also desirable for the working electrode to use a sample volume between and including 0.1 and 0.3 μΐ,, and desirably from about 0.15 to about 0.2 μΐ _^ , although other sample volumes are contemplated. It is contemplated that the sample size may even be smaller such as from about 0.05 to about 0.3 μί, and desirably from about 0.05 to about 0.2 μΐ _^ .

[0045] While the invention is susceptible to various modifications and alternative forms, specific embodiments and methods thereof have been shown by way of example in the drawings and are described in detail herein. It should be understood, however, that it is not intended to limit the invention to the particular forms or methods disclosed, but, to the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.