The present invention relates, in general, to test strips for measuring an analyte or indicator, such as glucose, in a physiological fluid such as blood, interstitial fluid, or urine. More particularly, the present invention relates to test strips incorporating a system which prevents the re-use of such test strips.
The present invention may be used in test strips for measuring an analyte or indicator such as glucose in a physiological fluid such as blood, interstitial fluid, or urine. The present invention also relates to test strips incorporating an integrated lance such as a needle, blade, or other sharp or skin puncturing device. Certain types of medical devices such as, for example, glucose test strips were intended to be tested only once and then disposed. This requirement is often needed because the reagent chemistry in many test strips is not suitable for measuring glucose a second time. However, it is possible that some users will accidentally test a previously used test strip. This could potentially become a problem if the glucose meter attempts to make a glucose measurement and outputs a result. Therefore, it is desirable that a single use test strip and meter have a mechanism for preventing a previously tested test strip from being reused.
Recently, micro-needles (e.g. lances) and test strips (e.g., electrochemical-based and photometric-based biosensors) have been integrated into a single medical device. These integrated medical devices can be employed, along with an associated meter, to monitor various analytes, including glucose. Depending on the situation, biosensors can be designed to monitor analytes in an episodic single-use format, semi-continuous format, or continuous format. The integration of a micro-needle and biosensor simplifies a monitoring procedure by eliminating the need for a user to coordinate the extraction of a sample from a sample site with the subsequent transfer of that sample to a biosensor. This simplification, in combination with a small micro-needle and a small sample volume, also reduces pain.
For the case in which test strips are integrated with a lancing device, there is an added potential problem in that the re-use of test strips may result in cross-contamination. The lancing portion of the integrated device may have blood remaining on it which could infect a second user who might accidentally use the test strip. Therefore, it is desirable that the meter and test strip system have a mechanism which prevents a previously used test strip from launching the lance mechanism.
In one embodiment of an analyte measurement system which prevents the reuse of a test strip according to the present invention, an analyte measuring system comprises a test strip for measuring an analyte electrochemically. In this embodiment of the invention, the test strip includes a frangible link disposed on the test strip. In a further embodiment, the frangible link comprises a conductive trace wherein the conductive trace is a material chosen from a group consisting of carbon, silver, platinum, palladium, gold, Ir, Pt, tungsten, copper, and aluminum. In a further embodiment of the present invention, the conductive trace has a positive temperature coefficient of resistance and includes a first electrical contact zone and second electrical contact zone, each adapted to receive a predetermined voltage from a meter.
In a further embodiment of the present invention, the conductive trace comprises a fuse zone located between the first and second electrical contact zone, wherein the fuse zone has a higher resistance than the first electrical contact zone and the second electrical contact zone. In a further embodiment the fuse zone melts when a predetermined voltage is applied between the first and second electrical contacts wherein the predetermined voltage ranges from about 1.5 volts to about 30 volts.
Further embodiments of the present invention may include: an analyte measuring system wherein the test strip includes an integrated lance; an analyte measuring system wherein the analyte is glucose; an analyte measuring system wherein the test strip includes a working electrode and a reference electrode; an analyte measuring system wherein a reagent layer is disposed on at least a portion of the working electrode; an analyte measuring system wherein the reagent layer comprises a redox mediator and a redox enzyme; and an analyte measuring system wherein the reagent layer comprises a silica filler.
The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:
Test strip 20, which may be rectangular or another shape, is constructed by using a fixing mechanism such as adhesive layer 38 to attach top layer 34 to bottom layer 36. In an embodiment of the invention, test strip 20 may have an approximate width of 0.22 inches (i.e. 5.6 mm) and an approximate length of 0.55 inches (i.e. 14 mm). In the embodiment of
Test strip 20 further includes a sample receiving chamber 41 which is formed by the aggregate lamination of bottom layer 36, adhesive layer 38, and top layer 34 which represent the respective floor, wall, and roof of sample receiving chamber 41. Test strip 20 may be, for example, a glucose test strip which uses electrochemistry to measure the amount of glucose in a bodily fluid, such as, for example, blood or interstitial fluid. Alternatively or additionally, test strip 20 may be, for example, a coagulation sensor which measures a physical characteristic of a body fluid such as viscosity, capacitance, resistance, and the like.
The use of integrated lance 22 in test strip 20 makes testing simpler by eliminating the step of manually transferring sample into sample receiving chamber 41. Many previous sensor systems require a lancing step using a dedicated lancing device followed by the manual manipulation of the test strip so that it can be dosed with sample. The use of integrated lance 22 allows fluid to seamlessly flow from the wound to sample receiving chamber 41 without removing integrated lance 22.
In an embodiment of the present invention, fuse 100 is deposed on substrate 53 by a process such as, for example, screen printing, sputtering, evaporation, electroless plating, ink jetting, sublimation, chemical vapor deposition, and the like. The geometry of fuse 100 may be formed by using a screen which selectively allows conductive material to pass through in a defined pattern such as the one shown in
As shown in
As part of bottom layer 36, first working electrode 48, second working electrode pad 50, and reference electrode 52 are deposed on substrate 53. Similar to fuse 100, first working electrode 48, second working electrode 50, and reference electrode 52 may be deposited using one of the previously mentioned techniques described for fuse 100 and indeed may be manufactured or deposited at the same time. The geometry of first working electrode 48, second working electrode 50, and reference electrode 52 may be formed by using a screen which selectively allows conductive material to pass through in a defined pattern. Suitable materials which may be used for first working electrode 48, second working electrode 50, and reference electrode 52 are Au, Pd, Ir, Pt, Rh, silver, silver chloride, stainless steel, doped tin oxide, carbon, and the like. Possible embodiments of the electrode geometry suitable for use with the subject invention include those described in U.S. Pat. Nos. 6,716,577; 6,620,310; 6,558,528; 6,475,372; 6,193,873; 5,708,247; 5,951,836; 6,241,862; 6,284,125; and 6,444,115, and International Patent Application Publications WO/0167099; WO/0173124; WO/0173109; and WO/0206806, the disclosures of which are herein incorporated by reference.
As part of bottom layer 36, substrate 53 may be an electrically insulating material such as plastic, glass, ceramic, and the like. In a preferred embodiment of this invention, substrate 53 may be a plastic such as, for example, nylon, polyester, polycarbonate, polyimide, polyvinylchloride, polyethylene, polypropylene, and PETG. In an embodiment of the invention, the material used for substrate 53 may be a polyester material (trade name Melinex® ST328) which is manufactured by DuPont Teijin Films.
As part of the bottom layer 36, insulation layer 44 may be printed or disposed over a portion of the conductive layer in order to define the electrode area which is wetted by a liquid sample. In an embodiment of this invention insulation layer 44 may be printed by using one of the aforementioned techniques described for fuse 100. In a preferred embodiment of this invention, insulation layer 44 may be printed by using screen printing techniques in either a flat bed process or in a continuous web process. A suitable material which may be used for insulation layer 44 is Ercon E6110-116 Jet Black Insulayer Ink which may be purchased from Ercon, Inc. It should be appreciated that to one skilled in the art that several different types of insulating material could be suitable for use in the described invention. In an embodiment of this invention, insulation layer 44 may have a height between 1 and 100 microns, more favorably between 5 and 25 microns, and yet even more favorably at about 5 microns.
As part of the bottom layer 36, reagent layer 46 may be printed by using one of the aforementioned techniques described for fuse 100. In a preferred embodiment of this invention, reagent layer 46 may be printed by using screen printing techniques. A non-limiting example of a suitable reagent or enzyme ink for use in he present invention can be found in issued U.S. Pat. Nos. 5,708,247 and 6,046,051; published international applications WO01/67099 and WO01/73124. In an embodiment of this invention where test strip 20 is a glucose sensor, reagent layer 46 may comprise a redox enzyme and a redox mediator. Examples of redox enzymes may include glucose oxidase, glucose dehydrogenase using either a methoxatin co-factor, or a nicotinamide adenine dinucleotide co-factor. Examples of redox mediators may include ferricyanide, phenazine ethosulphate, phenazine methosulfate, pheylenediamine, 1-methoxy-phenazine methosulfate, 2,6-dimethyl-1,4-benzoquinone, 2,5-dichloro-1,4-benzoquinone, phenathiazine derivatives, phenoxazine derivatives, metalloporphyrin derivatives, phthalocyanine derivatives, viologen derivatives, ferrocene derivatives, osmium bipyridyl complexes, ruthenium complexes and the like. It should be appreciated that one skilled in the art that variations of the previously described enzyme ink could be suitable for use in the described invention. In an embodiment of this invention, reagent layer 46 may have a height between 1 to 100 microns, and more favorably between 5 to 25 microns.
In an embodiment of the present invention, adhesive layer 38 includes at least portion of the walls of a sample receiving chamber 41. Adhesive layer 38 may be printed or disposed on top of a portion of insulation layer 44 and/or a portion of reagent layer 46 to at least partially form a sample receiving chamber 41 within test strip 20. Examples of methods to print adhesive layer 38 may be screen printing, gravure, and slot coating. In other embodiments, adhesive layer 38 may be a double sided pressure sensitive adhesive, a UV cured adhesive, heat activated adhesive, or a thermosetting plastic. As a non-limiting example, adhesive layer 38 may be formed by screen printing a pressure sensitive adhesive such as, for example, a water based acrylic copolymer pressure sensitive adhesive which is commercially available from Tape Specialties LTD in Tring, Herts, United Kingdom as part #A6435.
In an embodiment of this invention, the height or adhesive layer 38 may be between 4 and 140 microns. The minimal value for the adhesive height is bounded by the height of reagent layer 46 because it would be undesirable for top layer 34 to physically contact reagent layer 46 and result in possible damage to reagent layer 46. The maximum value of the adhesive height is bounded by the desire to reduce the overall sample volume of test strip 20. Other factors which may influence the selected adhesive height may be the desire to maintain conditions for semi-infinite diffusion in regards to the mediator oxidation (i.e. concentration of redox mediator which is sufficiently far from the electrodes are unperturbed by electrochemical reactions).
In an embodiment of this invention, adhesive layer 38 further includes a side clearance area 40 and a distal clearance area 42. The clearance areas within the adhesive may be used to provide an area in which side embossment spacer 26 can interface with insulation layer 44 in such a manner that top layer 34 forms the roof of sample receiving chamber 41. Adhesive layer 38 should have at least about a slightly greater height than side embossment spacers 26 and distal embossment spacer 28 so that the embossment spacers provide a mechanical stop to limit the compression of the adhesive height between the top layer 34 and bottom layer 36. Therefore, the use of embossment spacers or other mechanical protrusions help control the sample chamber height when using either heat activated adhesive or thermosetting plastic.
As an embodiment of the present invention, integrated lance 22 may be manufactured as an integral part of top layer 34. Integrated lance 22 may be formed in a stamping process where it has a “V” shaped open channel geometry. More details concerning the design of integrated lance 22 may be found in US provisional application Ser. No. 60/458,242 and 60/459,465 which are incorporated by reference herein. For certain embodiments of the invention, top layer 34 may be coated with a surfactant coating or undergo a hydrophilic surface treatment to in increase the capillary force of test strip 20. Non-limiting examples of surfactant coatings are Tween-80, JBR-515, Niaproof, and Tergitol. Integrated lance 22 may further include stiffening rib 24 as shown in
In addition, this method of the present invention can determine if a test strip has been previously used and prevent the user from testing a used test strip. If the meter determines that fuse 100 is discontinuous, then the meter will turn off and/or output an error message indicative of defective/used test strip as shown in step 460.
The purpose of fuse 100 is to reduce and effectively prevent the possibility that test strip 20 is reused. An embodiment of this invention includes top layer 34 having an integrated lance 22. Therefore, the reuse of test strip 20 can result in cross-contamination of physiological fluid or infection to the user. Therefore, it is desirable to have fuse 100 which can allow a meter to determine if test strip 20 has already been tested. The meter is designed to break fuse 100, or in some cases blow a fuse, after test strip 20 has been tested. If the meter determines that test strip 20 has been already tested (e.g. by testing that the fuse 100 is broken or the fuse is blown), the meter will either output an error message and/or prevent initiation of the test. However, if the meter determines that test strip 20 has not been tested, the meter will initiate the test by either launching integrated lance 22 towards the skin or prompting the user to do so by actuating a switch.
Strip insertion port 590 includes an opening or orifice within meter 500 that allows a portion of test strip 20 to be inserted into meter 500. More specifically, the proximal end of test strip 20 may be inserted into meter 500 such that electrical contact can be established with first working electrode 48, second electrode 50, reference electrode 52, and fuse 100.
The means for measuring glucose includes first working electrode contact 510, second working electrode contact 520, reference electrode contact 550, first test voltage source 560, and second test voltage source 570. Meter 500 is designed such that first working electrode contact 510, second working electrode contact 520, and reference electrode contact 550 establish electrical contact with first working electrode 48, second working electrode 50, and reference electrode 52, respectively, as shown in
The means for determining whether test strip 20 has been previously tested with a physiological fluid includes a first continuity contact 530, a second continuity contact 540, and a continuity voltage source 580. Meter 500 is designed such that first continuity contact 530 and second continuity contact 540 establish electrical contact with first electrical contact zone 101 and second electrical contact zone 102, respectively, as shown in
In an alternative embodiment to the present invention, continuity voltage source may apply a variable voltage such that a constant current is applied between first electrical contact zone 101 and second electrical contact zone 102. Next meter 500 interrogates test strip 20 for an electrical continuity between first electrical contact zone and second electrical contact zone which may determined by a measured non-infinite voltage value (as opposed to an infinite voltage value).
The means for blowing fuse 100 includes a voltage source or current source which may be applied across first continuity contact and second continuity contact. Because meter 500 is designed such that first continuity contact 530 and second continuity contact 540 establish electrical contact with first electrical contact zone 101 and second electrical contact zone 102, a sufficiently strong voltage or current
It is an advantage of this invention in that it is more reliable than existing techniques because it identifies a used test strip as soon as the test strip is inserted into the meter. This early detection capability is especially useful for test strips having an integrated lance 22 because reuse can be a source of contamination and infection.
It is an another advantage of this invention in that a used test strip can be identified by the meter even when the liquid sample applied to the test strip has dried. Impedance techniques for identifying a used test strip require liquid to be within the test strip.
It is another advantage of this invention in that a fuse can be added to the test strip at a low cost. It is a simple manufacturing step to print an additional electrode onto the test strip.
It is another advantage of this invention in that the circuitry required determining the continuity of a fuse is very simple and low cost.
While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to hose skilled in the art without departing from the invention.
It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.
This application is related to co-pending provisional application Ser. No. 60/422,228, filed on Oct. 30, 2002, entitled “Improved Method of Lancing Skin for the Extraction of Blood” (attorney docket number LFS-0264) which is hereby incorporated herein by reference. This application is also related to co-pending international application serial number PCT/GB01/05634, filed on Dec. 19, 2001, entitled “Analyte Measurement” which are hereby incorporated herein by reference. This application is also related to co-pending provisional application Ser. No. 60/458,242, filed on Mar. 28, 2003, entitled “Integrated Lance and Strip for Analyte Measurement” (attorney docket number LFS-5011) which are hereby incorporated herein by reference. This application is related to co-pending provisional application Ser. No. 60/459,465, filed on Mar. 28, 2003, entitled “Method of Analyte Measurement Using Integrated Lance and Strip” (attorney docket number LFS-5012) which are hereby incorporated herein by reference. This application is further related to co-pending patent application entitled “A Method of Preventing Reuse in an Analyte Measuring System” (attorney docket number LFS-5046) filed on ______, U.S. patent application Ser. No. ______.