Patent Application
20080020452
Reference will now be made in detail to the exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
According to exemplary embodiments, the invention relates to a system for measuring a body fluid constituent including a test strip and a meter. An individual test strip may also include an embedded code relating to data associated with a lot of test strips, or data particular to that individual strip. The embedded information presents data readable by the meter signaling the meter's microprocessor to access and utilize a specific set of stored calibration parameters particular to test strips from a manufacturing lot to which the individual strip belongs, or to an individual test strip. The system may also include a check strip that the user may insert into the meter to check that the instrument is electrically calibrated and functioning properly.
In addition, the present disclosure provides test strips that include electrical contacts that are resistant to scratching or abrasion. In other embodiments, the test strips of the present disclosure can include electrical contacts having material properties and dimensions such that, even when scratched or abraded, the test strips will continue to function properly. Such test strips can include conductive electrical contacts formed of two or more layers of material. A first lower layer can include a conductive metal, ink, or paste. A second upper layer can include a conductive ink or paste. Further, in some embodiments, the upper layer can have a resistance to abrasion that is greater than the lower layer. In addition, the second upper layer may have a thickness such that, even when scratched or abraded, the entire thickness of the conductive layer will not be removed, and the electrical contact will continue to function properly.
For purposes of this disclosure, “distal” refers to the portion of a test strip further from the fluid source (i.e. closer to the meter) during normal use, and “proximal” refers to the portion closer to the fluid source (e.g. a finger tip with a drop of blood for a glucose test strip) during normal use.
The test strip may include a sample chamber for receiving a user's fluid sample, such as, for example, a blood sample. The sample chamber and test strip of the present specification can be formed using materials and methods described in commonly owned U.S. Pat. No. 6,743,635, which is hereby incorporated by reference in its entirety. Accordingly, the sample chamber may include a first opening in the proximal end of the test strip and a second opening for venting the sample chamber. The sample chamber may be dimensioned so as to be able to draw the blood sample in through the first opening and to hold the blood sample in the sample chamber by capillary action. The test strip can include a tapered section that is narrowest at the proximal end, or can include other indicia in order to make it easier for the user to locate the first opening and apply the blood sample.
It should also be noted that although the test strip is shown as an elongated, approximately rectangular structure, the test strip can also include other shapes. For example, the test strip can also include tabs, discs, or any other suitable configuration, and although such configurations may not traditionally be considered ‘strips,’ it is understood that ‘test strip,’ as used herein, is understood to encompass any test media configuration suitable for use with a meter that makes electrical contact with a sample collection device (i.e. a test strip).
A working electrode and counter electrode can be disposed in the sample chamber optionally along with fill-detect electrodes. A reagent layer is disposed in the sample chamber and preferably contacts at least the working electrode. The reagent layer may include an enzyme, such as glucose oxidase or glucose dehydrogenase, and a mediator, such as potassium ferricyanide or ruthenium hexamine. The test strip has, near its distal end, a first plurality of electrical strip contacts that are electrically connected to the electrodes via conductive traces. In addition, the test strip may also include a second plurality of electrical strip contacts near the distal end of the strip. The second plurality of electrical contacts can be arranged such that they provide, when the strip is inserted into the meter, a distinctly discernable lot code readable by the meter. As noted above, the readable code can be read as a signal to access data, such as calibration coefficients, from an on-board memory unit in the meter.
In order to save power, the meter may be battery powered and may stay in a low-power sleep mode when not in use. When the test strip is inserted into the meter, the first and second plurality of electrical contacts on the test strip form electrical connections with corresponding electrical contacts in the meter. The second plurality of electrical contacts may bridge a pair of electrical contacts in the meter, causing a current to flow through a portion of the second plurality of electrical contacts. The current flow through the second plurality of electrical contacts causes the meter to wake up and enter an active mode. The meter also reads the code information provided by the second plurality and can then identify, for example, the particular test to be performed or a confirmation of proper operating status. In addition, based on the particular code information, the meter can also identify the inserted strip as either a test strip or a check strip. If the meter detects a check strip, it performs a check strip sequence. If the meter detects a test strip, it performs a test strip sequence.
In the test strip sequence, the meter validates the working electrode, counter electrode, and, if included, the fill-detect electrodes, by confirming that there are no low-impedance paths between any of these electrodes. If the electrodes are valid, the meter indicates to the user that a sample may be applied to the test strip. The meter then applies a drop-detect voltage between the working and counter electrodes and detects a fluid sample, such as, a blood sample, by detecting a current flow between the working and counter electrodes (i.e., a current flow through the blood sample as it bridges the working and counter electrodes). To detect that an adequate sample is present in the sample chamber and that the blood sample has traversed the reagent layer and mixed with the chemical constituents in the reagent layer, the meter may apply a fill-detect voltage between the fill-detect electrodes and measure any resulting current flowing between the fill-detect electrodes. If this resulting current reaches a sufficient level within a predetermined period of time, the meter indicates to the user that adequate sample is present and has mixed with the reagent layer.
The meter can be programmed to wait for a predetermined period of time after initially detecting the blood sample to allow the blood sample to react with the reagent layer. Alternatively, the meter may be configured to immediately begin taking readings in sequence. During a fluid measurement period, the meter applies an assay voltage between the working and counter electrodes and takes one or more measurements of the resulting current flowing between the working and counter electrodes. The assay voltage is near the redox potential of the chemistry in the reagent layer, and the resulting current is related to the concentration of the particular constituent measured, such as, for example, the glucose level in a blood sample.
In one example, the reagent layer may react with glucose in the blood sample in order to determine the particular glucose concentration. In one example, glucose oxidase or glucose dehydrogenase is used in the reagent layer. During a sample test, the glucose oxidase initiates a reaction that oxidizes the glucose to gluconic acid and reduces a mediator such as ferricyanide or ruthenium hexamine. When an appropriate voltage is applied to a working electrode relative to a counter electrode, the ferrocyanide is oxidized to ferricyanide, thereby generating a current that is related to the glucose concentration in the blood sample. The meter then calculates the glucose level based on the measured current and calibration data that the meter has been signaled to access by the code data read from the second plurality of electrical contacts associated with the test strip. The meter then displays the calculated glucose level to the user. Each of the above-described components and their interconnection will now be described.
The conductive pattern includes a plurality of electrodes 19 disposed on base layer 16 near proximal end 12, a plurality of electrical strip contacts 15 disposed on base layer 16 near distal end 14, and a plurality of conductive traces 17 electrically connecting the electrodes to the plurality of electrical strip contacts. For purposes of this application, the noun “contact” denotes an area intended for mechanical engagement with another corresponding “contact” irrespective of whether an electric circuit is completed or passes through the particular area.
In one embodiment, the plurality of electrodes 19 may include a working electrode, a counter electrode, and fill-detect electrodes. The conductive pattern may be produced by applying a conductive material to base layer 16. The electrode material may be provided by thin-film vacuum sputtering of a conductive material (e.g. gold) and/or a semiconductive material (e.g. indium-zinc oxide) onto the base layer 16. The resulting electrode layer can then by further patterned according to the specific application by forming particular conductive regions/pathways through a laser ablation process. Alternative materials and methods for providing a conductive pattern, in addition to screen printing, can be employed without departing from the scope of the invention.
In order to prevent scratching and other damage to the conductive traces 17, a dielectric insulating layer 18 can be formed over the conductive pattern along a portion of the test strip between the measuring electrodes and the plurality of electrical strip contacts. As seen in
Referring to
The first plurality of electrical strip contacts 46-52 are divided, for example, through breaks 54 formed through the underlying conductive pattern in the test strip 10. These breaks could be formed in the conductive pattern during printing, through a scribe process, laser ablation, or through a chemical/photo-etching type process. In addition, other processes of forming conductive breaks by removing a conductor in the test strip 10 may be used as would be apparent to one having ordinary skill in the art. An additional break 55 divides conductive region 44 from conductive region 42 within distal strip contact region 26, and a further break 57 separates the upper right-hand portion of distal strip contact region 26 to form a notch region 56, as will be described more fully in detail below.
Referring to
As seen in
In one embodiment, the connection between contacting pad 66 and connector contact 9 establishes a common connection to ground (or a voltage source where the polarity is reversed), thereby completing an electric circuit, which includes the meter and at least a portion of conductive region 42. The completion of this circuit can perform a meter wake-up function, providing a signal to the meter to power up from low-power sleep mode. Therefore, as illustrated in
In other words, during distal movement of test strip 10 within the connector channel 32, the common connection will not be established at the point connector contact 9 engages the extreme distal edge of test strip 10. Instead, common connection will be established only when the connector contact passes notch 56, and ink strip 73, if applied, and engages a conductive portion of contacting pad 66. Accordingly, the combination of a proximally positioned connector contact 9 and a non-conductive notch region 56 provides a more reliable connection between strip 10 and the meter.
As noted above, the contacting pads 58, 60, 62, 64, and 66 are configured to be operatively connected to the second plurality of connector contacts 40 within meter connector 30. Through this operative connection, the meter is presented with, and reads from the contacting pads, a particular code signaling the meter to access information related to a particular underlying test strip 10. The coded information may signal the meter to access data including, but not limited to, parameters indicating the particular test to be performed, parameters indicating connection to a test probe, parameters indicating connection to a check strip, calibration coefficients, temperature correction coefficients, pH level correction coefficients, hematocrit correction data, and data for recognizing a particular test strip brand.
One such code is illustrated in
An exemplary insulating material includes, but is not limited to, VISTASPEC HB Black, HB Yellow, HB Cyan, and BrightWhite HB available from Aellora™ Digital of Keene, N.H. The VISTASPEC HB and BrightWhite HB materials are hybrid UV-curable inks for use in elevated temperature piezo drop-on-demand ink jet arrays. This VISTASPEC ink is jetted at an elevated temperature, rapidly sets upon contact with the underlying substrate, and is then cured by UV radiation. The ink's properties include electrical insulation, resistance to abrasion from a meter's contacts, enhanced adhesion to an underlying conductive material, and beneficial visco-elastic characteristics. The material's visco-elastic characteristics minimize ink spreading on the underlying substrate. Furthermore, these visco-elastic characteristics enable this ink to be utilized with high print resolution piezo technology that enables accurate and precise patterning of the VISTASPEC ink onto the conductive electrode substrate. In addition, the visco-elastic characteristics of the VISTASPEC ink enables a sample as small as about an 80 picoliter drop to remain pinned at the location where it makes contact with the underlying substrate, thereby enabling precise pad sizes, positional accuracy, and precision of up to less than about 0.005 inches. As an example, printing of the insulating material can be accomplished through the use of a SureFire Model PE-600-10 single pass piezo drop-on-demand ink jet print engine, also available from Aellora™ Digital of Keene, N.H. As non-limiting examples, the above described ink jet print engine can utilize Nova and Galaxy model print heads available from Spectra Inc. of Lebanon, N.H.
Systems using a laser or chemical ablation process require significant time to precisely remove a particular pattern of preexisting material. Because coding of the strip occurs later in the assembly process than the ablation step, adding a non-conductive ink layer 75 to the contacting pads eliminates the tolerance issues that would result from reintroducing strips into a larger ablation process for coding. Such printing of a dielectric insulation coating is advantageous in that it can be applied later in the strip manufacturing process and in an easily programmable and/or reproducible pattern. As a non-limiting example, the method of providing layer 75 to the underlying substrate can include the use of at least one registration datum along the underlying strip to insure accurate formation of the layer 75 according to a particular desired pattern. For example, datums can be provided orthogonally (e.g. longitudinally and laterally) along a substrate where that can be mechanically or optically referenced by a printing apparatus to facilitate the formation of an accurate and reproducible pattern.
Upon connection of the contacting pads 58, 60, 62, 64, and 66 in
Upon reading a particular code, an internal memory within the meter can access, through a stored microprocessor algorithm, specific calibration information (such as, for example, calibration coefficients) relating to the particular test strip. The meter can read the code through either an analog or digital method. In the analog mode, a preset resistive ladder is interconnected within the meter to the second plurality of connector contacts 40 (labeled 5-9 in
As further seen in
In the digital mode, as schematically represented in
Pads including non-conductive ink 75 with levels of high and low impedance produce a binary code yielding a code index based on the number of pads (P) implemented, where the number of codes is N=2P. The number of codes possible when integrated with an auto-on/wake-up feature is reduced to N=2P−1. Accordingly, a code with all zeros (all insulators) is not an active code as it will not wake up the meter.
When a strip 10 is inserted into the meter connector 30, one contact is closed and wakes up the meter by pulling the microcontroller's interrupt either high or low. The meter will then check the voltage out (Vout) to determine the test type and read the code bits (S1, S2, S3, S4) to determine the code value. The code value can, for example, be associated with a stored set of coefficients in the meter's memory for use in a glucose-mapping algorithm that is particularly correlated to the reagent applied to the measuring electrode region. This code can also be associated with other types of strip parameter information, such as those referenced above. It could also select different meter configuration options as well. The voltage drop across the series resistor R at Vout in
In addition to providing either a high or low impedance level through the application or absence of an insulating layer of non-conductive ink 75 over one of the contacting pads, a particular resistive element may be applied over a particular contacting pad. The resistive element introduces an increased level of impedance into a circuit that reduces, but does not necessarily prevent, the flow of electric current. Accordingly, the use of a specific resistive element over a particular contacting pad provides an intermediate level of resistance to the contacting pad of the test strip. When this intermediate level of resistance is connected to the meter through engagement with a corresponding meter connector contact, the meter can detect this “intermediate” level (e.g. through a circuit measurement of voltage drop by applying Ohm's and Kirchhoff's laws).
The detection of such an intermediate level can alert the meter's processor to access a new set of code data relating to the particular test strip. In other words, a resistive element coating can be used to expand the number of codes available with a set number of contacting pads. For example, a strip may be formed with a particular code through a particular pattern of non-conducting insulating ink 75. When one of the conducting contact pads is formed to include a particular resistive element, that same code represented by the pattern of non-conducting ink 75 now can be read by the meter to access an entirely different set of data.
As an example, the contacting pad 66 of
It should be noted that the particular disclosed configurations of test strip 10, including the configuration of connector contacts 38, 40 and the corresponding first and second plurality of electrical strip contacts, are merely exemplary, and different configurations could be formed without departing from the scope of the invention. For example, the underside of strip 10 can be formed to incorporate an additional number of contacting pads in order to increase the size (and thereby the amount of information) in the code index. The additional contacting pads on the underside of strip 10 could represent a third plurality of electrical strip contacts, thereby increasing the number of codes available.
The incorporation of individualized code data within individual test strips provides numerous advantages in addition to those associated with accuracy of measurement. For example, with individual strip coding, a user no longer needs to manually enter the meter's lot code, thereby removing the possibility of user error for this step. Strip lot codes stored directly on individual test strips will also provide a means to ship mixed lots of strips in a single strip vial. In contrast, current technologies such as button/key coding require all strips (typically packaged in a vial including 50 strips from the same lot) in a vial to be from the same lot code.
Individual strip coatings also afford bulk packaging benefits. For example, mixed lot test strips and vials including different numbers of strips will be possible. Strips from various lots could be stored in a central location and packaged for sale without the added time and expense required to provide strips that are packaged from a single lot. Individual lot calibration codes stored on strips can also provide a means for varying a code across a single lot should a strip lot have variation from beginning to end, or anywhere in between. Predetermined variations in manufacturing within a strip lot can be corrected by applying a continuously changing code across the lot, thereby solving yield problems and improving in-lot strip-to-strip variation. In addition, embedding lot codes on individual strips can be used to distinguish different types of test strips (e.g. glucose vs. ketone), identify check strips, or identify different manufacturing procedures, provide data for meter upgrades, and to correlate particular test strips for use only with a specific meter or meter type.
As noted previously, in some embodiments, the test strips of the present invention can include a conductive pattern including at least one electrical strip contact. The electrical strip contacts may be disposed at the distal end 14 of a test strip 10, such that the electrical strip contacts may form electrical contacts with connector contacts 38, 40 of a test meter. In some embodiments, it may be desirable to produce electrical strip contacts using more than one layer of material. For example, in some embodiments, a first conductive material may be applied to the base layer 16 to form a conductive pattern. Subsequently, a second conductive material may be applied over the first conductive material. Further, in some embodiments, the second conductive material may be selected such that the second conductive material has a higher resistance to abrasion than the first conductive material.
As shown, contacts 42′, 44′ can include two layers 900, 910. In some embodiments, first layer 900 may be disposed directly on base layer 16′, and second layer 910 may be applied on top of first layer 900. Further, first layer 900 may include a conductive metallic material, such as gold, titanium, palladium, silver, platinum, copper, or any other suitable metallic conductor. Alternatively, first layer 900 may include a conductive material, including, for example, a carbon-based material (e.g. carbon/graphite paste), copper pastes/inks, silver paste/inks, gold pastes/inks, palladium pastes/inks, and/or any other suitable paste or ink. In addition, second layer 910 may include a conductive material, including, for example, a carbon-based material (e.g. carbon/graphite paste), copper pastes/inks, silver paste/inks, gold pastes/inks, palladium pastes/inks, and/or any other suitable paste or ink.
It should also be noted that one or more semiconductive layers may be included. For example, it may be desirable to include a semiconductive layer 902 below the first layer 900 and in contact with base 16. Alternatively, a semiconductive layer 904 may be placed on top of first layer 900, and between first layer 900 and second layer 910. Suitable semiconductive materials may include, for example, indium-zinc oxide. The specific semiconductive materials may be selected based on desired electrical properties, and/or their ability to adhere to the base 16, first layer 900, and/or second layer 910. Further, in some embodiments, first layer 900 may include only a semiconductive material having sufficient thickness to provide adequate electrical conduction.
In addition, in some embodiments, first layer 900 may include a conductive layer, including for example, a metallic conductor such as gold. In addition, an adhesion layer may be placed between a metallic gold layer 900 and substrate base 16, at a position consistent with layer 902, as shown in
As noted previously, the first layer 900 can be produced using a variety of suitable deposition processes. After the first layer 900 is produced, the second layer 910 may be applied on top of the first layer 900. In some embodiments, the contact patterns, including first layer 900 and second layer 910, may be produced by collectively forming breaks in both first and second layers 900, 910, either simultaneously, or sequentially. As described previously, such breaks may be formed using various scribing processes, laser ablation, and/or through chemical/photo-etching processes. A number of suitable laser ablation processes may be used to produce a desired pattern for the electrical contacts. For example, one suitable laser ablation system includes a Nd:YVO4 Prisma 1064-32-V laser by Coherent. However, any suitable laser may be selected to produce desired material dimensions and patterns.
The second layer may be produced using a variety of suitable deposition processes. The specific process may be selected based on cost, desired feature dimensions, and/or the specific materials selected for the second layer 910. In some embodiments, the second layer 910 may be produced using a screen-printing process, a gravure printing process, an ink-jet process, a spray printing process, and/or flexographic printing processes. Further, a variety of suitable materials may be selected for second layer 910. For example, suitable materials can include various conductive pastes and/or inks. Suitable pastes and/or inks can include, for example, carbon/graphite paste (Gwent Electronic Materials Ltd, C2000802D2), water-based silver ink (Acheson, PE-001), water-based carbon ink (Acheson, PE-003), conductive graphite coating (Acheson, SS 24600), extremely conductive silver ink (Creative Materials, 124-12), polymer thick film conductive silver coating (Ercon, E-1649B), polymer thick film conductive silver coating (Ercon, E-1400), water-based silver conductive composition (DuPont, 5069), carbon conductive composition (DuPont, 5067), silver conductor paste (DuPont, 5000), carbon conductor paste (DuPont, 5085), silver/carbon conductor paste (DuPont, 5524), inkjet silver conductor (Cabot, AG-IJ-G-100-S1).
In some embodiments, the selected application process may be based on the desired layer thickness, and/or material type. For example, suitable processes for depositing layers of conductive inks with thicknesses ranging from about 1 micron to about 50 microns can include gravure printing, ink jet printing, spray deposition. For materials from about flexography for thicknesses of about 1 micron to about 15 microns, flexography may be selected. For thicker films (e.g. about 10 microns to about 50 microns) screen printing processes may be employed. Printed inks may be cured using ovens, IR heat sources, or UV lamps for about 5 seconds to about 5 min depending on ink formulation requirements.
Suitable materials for the second layer 910 may be selected to provide increased resistance to abrasion by electrical contacts 38, 40. Abrasion by contacts 38, 40 can disrupt electrical connections with a meter and also alter the calibration data provided by electrical contact patterns. In addition, material abraded by contacts 38, 40 may collect within a test meter connection region, potentially disrupting future tests. Therefore, in some embodiments, the second layer 910 may be produced with a thickness sufficient to prevent abrasion through second layer 910 and/or first layer 900. A range of suitable thicknesses may be included for first layer 900 and/or second layer 910. For example, first layer 900, with or without one or more semiconductive layers 902, 904) may be between about 1 and about 50 microns thick. Further, second layer 910 may be between about 10 microns and about 60 microns. In addition, in some embodiments, second layer 910 may be thicker than first layer 900.
In some embodiments, as noted previously, one or more regions of insulative material 75′ may be applied either over conductive region 42′, 44′. The insulative material may be applied in a pattern corresponding to a calibration code, as described previously. In some embodiments, the material from second layer 910 may be selected to have a high degree of adhesion to the insulative material 75′. For example, second layer 910 and insulative material 75′ may have a higher degree of adhesion than metallic materials used for first layer 900 and insulative material 75′. Therefore, the use of the second layer 910 may further improve adhesion of insulative material 75′, thereby preventing abrasion of insulative material 75′, and preventing erroneous readings due to loss of insulative material 75′.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
