Patent Application
20130199942
1. Field of the Invention
The present invention relates, in general, to medical devices and, in particular, to analytical test strips and related methods.
2. Description of Related Art
The determination (e.g., detection and/or concentration measurement) of an analyte in a fluid sample is of particular interest in the medical field. For example, it can be desirable to determine glucose, ketone bodies, cholesterol, lipoproteins, triglycerides, acetaminophen and/or HbA1c concentrations in a sample of a bodily fluid such as urine, blood, plasma or interstitial fluid. Such determinations can be achieved using analytical test strips, based on, for example, visual, photometric or electrochemical techniques. Conventional electrochemical-based analytical test strips are described in, for example, U.S. Pat. Nos. 5,708,247, and 6,284,125, each of which is hereby incorporated in full by reference.
The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention, in which:
The following detailed description should be read with reference to the drawings, in which like elements in different drawings are identically numbered. The drawings, which are not necessarily to scale, depict exemplary embodiments for the purpose of explanation only and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.
As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein
In general, electrochemical-based analytical test strips for the determination of an analyte (such as glucose) in a bodily fluid sample (for example, whole blood) according to embodiments of the present invention include an electrically insulating substrate layer with a distal end and a patterned conductor layer that is disposed over the electrically-insulating substrate layer and has a working electrode and a counter/reference electrode. The electrochemical-based analytical test strips also include a patterned insulation layer with an electrode exposure window configured to expose a working electrode exposed portion and a counter/reference electrode exposed portion, a reagent layer, and a pattered spacer layer. In addition, the patterned insulation layer and the patterned spacer layer define a sample receiving chamber with a sample-receiving opening at the distal end of the electrically insulating substrate layer and that extends across the working electrode exposed portion and the counter/reference electrode exposed portion. Moreover, the reagent layer is disposed over the working electrode exposed portion and the counter/reference electrode exposed portion and extends no more than 400 μm toward the sample-receiving opening beyond the distal most of the working electrode exposed portion and the counter/reference electrode exposed portion.
Electrochemical-based analytical test strips according to embodiments of the present invention are beneficial in that, for example, the fill speed of the electrochemical-based analytical test strip (e.g., the time for a bodily fluid sample to travel from one point to another point in a same-receiving chamber of the electrochemical-based analytical test strip (in this case it is the time taken for fluid to travel between a first working electrode and a second working electrode. The start and end times of the speed measurement are triggered by an increase in current beyond a pre-determined threshold—in this case the threshold current is 150 nA) and fill speed variability are beneficially optimized. Reduction in fill speed reduces the risk of generating a fill speed-related error message during analyte determination (the error risk is related to the accuracy check performed by the meter on the end currents of the first and second working electrodes. If a strip fills too slowly, the end currents of the first and second working electrodes may be sufficiently different to cause an Error 5 message i.e. >20% difference in end current after 5 seconds) and also reduces the delay experienced by a user in receiving determination results. A reduction in fill speed variability reduces a user's perception of strip-to-strip variation that can cause concern or annoyance.
Referring to
The disposition and alignment of electrically-insulating substrate layer 120, patterned conductor layer 140 (which includes a counter/reference electrode 140a, a first working electrode 140b and a second working electrode 140c, see
Although, for the purpose of explanation only, electrochemical-based analytical test strip 100 is depicted as including three electrodes, embodiments of electrochemical-based analytical test strips, including embodiments of the present invention, can include any suitable number of electrodes.
Counter/reference electrode 140a, first working electrode 140b, and second working electrode 140c can be formed of any suitable material including, for example, gold, palladium, platinum, indium, titanium-palladium alloys and electrically conducting carbon-based materials. Referring in particular to
Electrically-insulating substrate layer 120 can be any suitable electrically-insulating substrate layer known to one skilled in the art including, for example, a nylon substrate, polycarbonate substrate, a polyimide substrate, a polyvinyl chloride substrate, a polyethylene substrate, a polypropylene substrate, a glycolated polyester (PETG) substrate, or a polyester substrate. The electrically-insulating substrate layer can have any suitable dimensions including, for example, a width dimension of about 5 mm, a length dimension of about 27 mm and a thickness dimension of about 0.5 mm.
Electrically-insulating substrate layer 120 provides structure to the strip for ease of handling and also serves as a base for the application (e.g., printing or deposition) of subsequent layers (e.g., a patterned conductor layer). It should be noted that patterned conductor layers employed in analytical test strips according to embodiments of the present invention can take any suitable shape and be formed of any suitable materials including, for example, metal materials and conductive carbon materials.
Patterned insulation layer 160 can be formed, for example, from a screen printable insulating ink. Such a screen printable insulating ink is commercially available from Ercon of Wareham, Mass. U.S.A. under the name “Insulayer.”
Patterned spacer layer 220 can be formed, for example, from a screen-printable pressure sensitive adhesive commercially available from Apollo Adhesives, Tamworth, Staffordshire, UK. In the embodiment of
Hydrophilic layer 240 can be, for example, a clear film with hydrophilic properties that promote wetting and filling of electrochemical-based analytical test strip 100 by a fluid sample (e.g., a whole blood sample). Such clear films are commercially available from, for example, 3M of Minneapolis, Minn. U.S.A. If desired, patterned spacer layer 220, hydrophilic layer 240 and top layer 260 can be integrated into a single component 260′ as depicted in
Enzymatic reagent layer 200 can include any suitable enzymatic reagents, with the selection of enzymatic reagents being dependent on the analyte to be determined. For example, if glucose is to be determined in a blood sample, enzymatic reagent layer 200 can include a glucose oxidase or glucose dehydrogenase along with other components necessary for functional operation. Enzymatic reagent layer 200 can include, for example, glucose oxidase, tri-sodium citrate, citric acid, polyvinyl alcohol, hydroxyl ethyl cellulose, potassium ferrocyanide, antifoam, cabosil, PVPVA, and water. Further details regarding enzymatic reagent layers, and electrochemical-based analytical test strips in general, are in U.S. Pat. Nos. 6,241,862 and 6,733,655, the contents of which are hereby fully incorporated by reference.
Referring to
Referring to
It has been determined that electrochemical-based analytical test strips according to embodiments of the present invention are particularly beneficial with respect to optimizing fill speed and fill variability when the enzymatic reagent layer is relatively hydrophilic and/or has a chalky texture (i.e., has a powdery texture) prior to application of a bodily fluid sample to the electrochemical-based analytical test strip. It is hypothesized without being bound that chalky enzymatic reagent layers exhibit poor adhesion to the electrically-insulating substrate layer at a microscopic level that interferes with bodily fluid flow. Enzymatic reagent layers that contain silica can be relatively hydrophilic and/or have a chalky texture. Therefore, electrochemical-based analytical test strips according to embodiments of the present invention are also particularly beneficial when the enzymatic reagent layer contains silica.
Electrochemical-based analytical test strip 100 can be manufactured, for example, by the sequential aligned formation of patterned conductor layer 140, patterned insulation layer 160, enzymatic reagent layer 200, patterned spacer layer 220, hydrophilic layer 240 and top layer 260 onto electrically-insulating substrate layer 120. Any suitable techniques known to one skilled in the art can be used to accomplish such sequential aligned formation, including, for example, screen printing, photolithography, photogravure, chemical vapour deposition and tape lamination techniques.
Method 600 also includes measuring an electrochemical response of the electrochemical-based analytical test strip (see step 620 Of
Once apprised of the present disclosure, one skilled in the art will recognize that method 600 can be readily modified to incorporate any of the techniques, benefits and characteristics of electrochemical-based analytical test strips according to embodiments of the present invention and described herein.
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 those 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 devices and methods within the scope of these claims and their equivalents be covered thereby.
