Patent Application
20130341207
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 and/or the determination of a characteristic of a fluid sample (such as haematocrit) are 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, analytical test strips (e.g., 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 first and second capillary sample-receiving chambers and first and second stop junctions that are disposed between the first and second capillary sample-receiving chambers. The first stop junction defines a discontinuity boundary of the first capillary sample-receiving chamber and the second stop junction defines a discontinuity boundary of the second capillary sample-receiving chamber. In addition, the first stop junction and the second stop junction are disposed such that bodily fluid sample flow between the first capillary sample-receiving chamber and the second capillary sample-receiving chamber is prevented during use of the analytical test strip.
When fluid flows through a capillary channel or chamber, a discontinuity in surface tension can cause a back pressure that prevents the fluid from proceeding through the discontinuity. Such a discontinuity is referred to as a “stop junction” and can be caused by, for example, an abrupt change in channel cross-section (i.e., a change in a channel or chamber dimension) and/or a change in the hydrophilic and/or hydrophobic nature of the surfaces defining the channel or chamber. Stop junctions based on changes in channel cross-section are described, for example, in U.S. Pat. Nos. 6,488,827, 6,521,182 and 7,022,286, each of which is hereby incorporated in full by reference.
Analytical test strips according to embodiments of the present invention are beneficial in that, for example, the stop junction(s) serves to maintain the fluidic integrity of the first and second capillary sample-receiving chambers while also being relatively small and easily manufactured. Such fluidic integrity beneficially prevents mixing of reagents and reaction byproducts between the first and second capillary sample-receiving chambers that can lead to inaccuracies in analyte or bodily fluid sample characteristic determination. Moreover, since the stop junctions are relatively small, sample application openings for the first and second capillary sample application chambers can be juxtaposed close to one another (for example, separated by a distance of approximately 250 microns that can be operatively bridged by a whole blood sample of approximately 1 micro-liter) such that the single application of a bodily fluid sample bridges both sample application openings and fills both the first and the second capillary sample-receiving chambers.
Referring to
The disposition and alignment of electrically-insulating substrate layer 120, patterned conductor layer 140 (which a variety of electrodes 140a, see
Moreover, the disposition is also such that a first stop junction 266 (delineated by dashed lines in
The first stop junction and the second stop junction are disposed such that bodily fluid sample flow between the first capillary sample-receiving chamber and the second capillary sample-receiving chamber during use of the analytical test strip is prevented. In the embodiment of
It should be noted that in the embodiments depicted in
In the perspective of
Patterned conductor layer 104, including electrodes 140a, of analytical test strip 100 can be formed of any suitable material including, for example, gold, palladium, platinum, indium, titanium-palladium alloys and electrically conducting carbon-based materials including carbon inks. Referring in particular to
During use, a bodily fluid sample is applied to electrochemical-based analytical test strip 100 and fills both the first and second capillary sample-receiving chambers by capillary action and, thereby, operatively contacts the electrodes disposed in the first and second capillary sample-receiving chambers. Referring 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 0.35 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, or other suitable materials such as, for example, polyester and polypropylene. The thickness of patterned spacer layer 220 can be, for example 75 um. 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. and Coveme (San Lazzaro di Savena, Italy). Hydrophilic layer 240 can be, for example, a polyester film coated with a surfactant that provides a hydrophilic contact angle <10 degrees. Hydrophilic layer 240 can also be a polypropylene film coated with a surfactant or other surface treatment, e.g., a MESA coating. Hydrophilic layer 240 can have a thickness, for example, of approximately 100 μm.
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.
Top layer 260 can be formed of any suitable mater including, for example, polyester materials, polypropylene materials, and other plastic materials. Top layer 260 can have a thickness, for example of approximately 50 μm.
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.
Hydrophobic layer 410 can be formed, for example, from any suitable hydrophobic material such as a PTFE material, a carbon ink material, or other suitable hydrophobic material with a contact angle of, for example, greater than 100 degrees.
In each of electrochemical-based analytical test strips 300, 400 and 500, their respective hydrophobic layers serve together create a surface tension-induced back-pressure that either fully defines the first and second stop junctions (see the embodiment of
Method 900 also includes measuring a first response of the analytical test strip (for example an electrochemical response from electrodes in the first capillary sample-receiving chamber) and determining an analyte in the bodily fluid sample is determined based on the first measured electrochemical response (see steps 920 and 930 of
In steps 940 and 950 of method 900 also includes, measuring a second response of the analytical test strip (for example, an electrical response from electrodes in the second capillary sample-receiving chamber) and determining a characteristic of the bodily fluid sample based on the second measured response. The measuring and determination steps described above can, if desired, by performed using a suitable associated meter and measurement steps 920 and 930 can be performed in any suitable sequence or in an overlapping manner.
Once apprised of the present disclosure, one skilled in the art will recognize that method 900 can be readily modified to incorporate any of the techniques, benefits and characteristics of 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.
