Test Strip for Holding Reagents to Determine Blood Glucose Level

Abstract

This invention relates to a test strip for holding reagents to determine blood glucose level, said strip comprising a) a plasma separator membrane which is a composite membrane for separation of plasma from whole blood, said plasma separator membrane containing an enzyme mix specific to the analyte, said analyte being glucose, a substrate which reacts specifically with one of the products of the enzymatic reaction of the analyte with the enzyme mix, b) a reaction membrane containing an enhancer mix of metallic ions, which enhances the color developed due to the enzymatic reaction.

Claims

1. A test strip for holding reagents to determine blood glucose level, said strip comprising a) a plasma separator membrane which is a composite membrane for separation of plasma from whole blood, said plasma separator membrane comprising an enhancer mix of metallic ions, which enhances a color developed due to an enzymatic reaction of an analyte with an enzyme mix; b) a reaction membrane comprising the enzyme mix specific to the analyte, said analyte being glucose; and a chromogenic substrate which reacts specifically with a product of the enzymatic reaction of the analyte with the enzyme mix.

2. The test strip as claimed in claimed in claim 1, wherein said plasma separator membrane is made up of polysulphone, cellulose, nitrocellulose and glass fibres, preferably polysulphone.

3. The test strip as claimed in claim 1, wherein said composite membrane has specific dimensions and is positioned in said test strip for the purpose of plasma separation from the whole blood.

4. The test strip as claimed in claim 1, wherein said enzyme mix comprises a glucose oxidase and a peroxidase.

5. The test strip as claimed in claim 1, wherein said chromogenic substrate is specific to the product of said enzymatic reaction and develops a colored product by reacting with the product of said enzymatic reaction.

6. The test strip as claimed in claim 5, wherein said chromogenic substrate is selected from the group of compounds 3,3,5,5-Tetramethylbenzidine, 2,2-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid),3,3-diaminobenzidine and o-Phenylenediamine.

7. The test strip as claimed in claim 5, wherein said enhancer mix enhances the of said colored product.

8. The test strip as claimed in claim 1, wherein the enhancer mix is present in dried form in the plasma separator membrane.

9. The test strip as claimed in claim 1, wherein said enhancer mix is a metal salt selected from a group consisting of copper sulfate, nickel chloride, nickel ammonium sulfate and cobalt chloride.

10. A process for the preparation of the test strip, comprising the steps of preparing a mix of glucose oxidase and peroxidase in a citrate buffer, spreading the mix on a cellulose sheet, drying the cellulose sheet, adding a substrate on the mix, drying the substrate to obtain a reaction strip, preparing a solution of an enhancer in a buffer, and quenching a membrane with the enhancer. drying the membrane to obtain a plasma separator membrane, placing said reaction strip below said plasma separator membrane to obtain a sandwich, and by placing said sandwich on an additional membrane to obtain the test strip.

11. The process as claimed in claim 10, wherein said citrate buffer has a pH between 5 to 6, such as citrate buffer.

12. The process as claimed in claim 10, wherein said additional membrane is comprises a porous fabric or material such as polyamide, polyolefin, polysulfone, or cellulose.

Description

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0013] FIG. 1 is a front view of the test strip.

[0014] FIG. 2 is elevated view of the composite and circular disks upon which reagents and enzymes are immobilized.

[0015] FIG. 3 Graph showing the comparison between liquid assay and the Glucose estimating strips and nanoamperometric glucometer.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Thus according to this invention is provided a test strip for determination of blood glucose level in plasma.

[0017] In accordance with this invention, the test strip for blood glucose determination is made by assembling plasma separator, enhancer, enzyme mix and a chromogenic substrate.

[0018] The FIG. 1 represents the sequential arrangement of various components of the said test strip from the front.

[0019] The test strip comprises :

[0020] a) a plasma separator membrane which is a composite membrane for separation of plasma from whole blood, said plasma separator membrane containing

[0021] an enzyme mix specific to the analyte, said analyte being glucose,

[0022] a substrate which reacts specifically with one of the products of the enzymatic reaction of the analyte with the enzyme mix,

[0023] b) a reaction membrane containing an enhancer mix of metallic ions, which enhances the color developed due to the enzymatic reaction.

[0024] The composite membrane for separation of plasma i.e. the plasma separator is a membrane made of polysulphone, cellulose, nitrocellulose and glass fibres, preferably polysulphone. It has specific dimensions and it is and positioned in said test strip for the purpose of plasma separation from whole blood by entrapping cellular components specially the red blood cells. The polysulphone plasma separator prevents red blood cell leakage into the reaction area.

[0025] The enzyme mix is composed of glucose oxidase and peroxidase. The substrate is specific to one of the products of the enzymatic reaction, and develops a coloured product by reacting with one of the products of the enzymatic reaction. The substrate is selected from a group of 3,3,5,5-Tetramethylbenzidine, 2,2-azino-bis(3-ethyl benzothiazoline-6-sulphonic acid), 3, 3-diaminobenzidine and o-phenylenediamine.

[0026] The enhancer used in the test strip is used for enhancing the colour produced by the enzymatic reaction. The enhancer is present in dried form in the plasma separator. The enhancer is a metal salt selected from a group consisting of copper sulfate, nickel chloride, nickel ammonium sulfate and cobalt chloride and the ratio of metallic ions is specifically optimized for the substrate. The test strip consists of a porous fabric or material such as polyamide, polyolefin, polysulfone, or cellulose. The test strip is composed of two layers wherein plasma separator membrane is placed on top of the reaction membrane and is based on standard glucose oxidase-peroxidase enzymatic method wherein the final concentrations of both enzymes in the mixture are in a specified ratio based on the source of the enzyme.

[0027] The enzymes are mixed in a buffer of pH around 5 to 6 and a homogeneous mixture is prepared. In a preferred embodiment the peroxidase is horseradish peroxidase and the buffer is a citrate buffer.

[0028] After mixing thoroughly to obtain a homogeneous blend, the mix is spread on a cellulose sheet and dried at 20-25 C. The sheet is then cut into strips of the desired size and shape. The strips may be circular, square or rectangular. Next, the substrate is mixed with a buffer of pH between 5 to 6 such as citrate buffer and a homogeneous solution is made. This solution is spread on the cellulose sheet containing the enzyme mix, once the enzymes have dried completely. The cellulose strip containing the enzyme mix and the substrate is allowed to dry under dark conditions to avoid photooxidation of the substrate, to obtain the reaction membrane.

[0029] The enhancer mix is prepared by adding one or more salts in a citrate buffer of pH between 5 to 6 such as citrate buffer. The enhancer mix is spread on the plasma separator membrane and dried at a temperature of 20-25 C. To assemble the test strip, the reaction cellulose strip containing enzyme mix and substrate is placed below the plasma separator containing the enhancer mix to obtain a composite sandwich. The sandwich is again mounted on an additional membrane for additional structural integrity such as a HiPP strip. The membrane sandwich is protected from moisture and dust by covering with wide polyester mesh strips over them.

[0030] In the test strip (1), blood is placed on the membrane (2) which separates red blood cells from plasma thus allowing only clear plasma to react with enzymes immobilized on cellulose membrane (3). The reaction occurs in reaction membrane (3) that produces hydrogen peroxide, which reacts with its substrate present along with the said enzyme mix and produces a colored complex. Enhancer mix of heavy metals is present in dried form in membrane (2), which travels with plasma and intensifies the developed colour complex. The final reaction and intensification occur on membrane (2). The measurable signal, blue colour in this case, develops on the said reaction mixture. The chromogenic reaction produces color that is directly proportional to glucose concentration present in plasma. The enzyme mix comprises glucose oxidase and peroxidase which is immobilized on a cellulose membrane. Glucose present in the separated plasma reacts with enzyme mix to produce hydrogen peroxide which forms a light brown color complex with said chromogenic substrate. At this stage, enhancer mix present in plasma separation membrane turns developed brown color into intensified blue color complex. The final blue color is a function of glucose concentration present in plasma. The invention will now be explained in greater detail with the help of the following non-limiting examples.

Example 1

[0031] The test strip is composed of two layers wherein plasma separation membrane is placed on top of a reaction membrane and is based on standard glucose oxidase-peroxidase enzymatic method wherein the final concentrations of both enzymes in the mixture are in a specified ratio based on the source of the enzyme. For example 625 units horseradish peroxidase and 2,500 units glucose oxidase in 10 mL of citrate buffer, pH 5.4 were mixed arid a homogeneous mixture of the enzymes was prepared. After mixing to ensure a homogeneous blend, the said enzyme mix was homogenously spread onto a cellulose sheet and dried at 22 C. The rows were then cut into strips of the desired size. Next, 25 mg of 3, 3-diaminobenzidine was mixed with 10 ml of citrate buffer pH 5.4 and a homogenous solution of the chromogen is made. This chromogenic mix is spread on cellulose paper once the enzyme mix has been dried completely and allowed to dry under dark conditions. Then, enhancer mix was prepared by adding Cobalt Chloride (2%) and Nickel chloride (2%) in 4:1 ratio in citrate buffer, pH 5.4. The plasma separator membrane was quenched with the enhancer mix and dried at 22 C. To assemble the glucose test strip, cellulose disc (4 mm4 mm) containing enzyme mix specific for analyte, in this case glucose, was placed below the said plasma separator containing enhancer mix (5 mm5 mm). The sandwich of the discs is mounted on a HiPP strip of 5 mm6 cm for added structural integrity. The membrane sandwich is protected from moisture and dust by a covering of 5 mm wide polyester mesh strips (Scrynel PET230 HC), 50 microns thick, applied over the top of the paper sensors. These strips were packaged with absorbent packs of silica gel.

Example 2

[0032] 1. Glucose test strips in accordance with the invention were made in accordance with Example #1

[0033] 2. Blood is dropped on plasma separator which prevents red blood cell leakage to the reaction area. A color signal generated by the said enzymatic reaction in the presence of glucose and is read by the glucometer provided and converted into glucose value in mg/dL or mmol/L.

[0034] 3. The final color on the membrane is read using a specifically designed Glucometer which houses an LED, an optical sensor, a microprocessor that receives digital signals from the optical sensor and converts the frequency values to glucose concentration based on preset algorithm incorporated in the microprocessor.

[0035] 4. The glucometer allows for storing 50 previous values and also displays errors in case the strip is inserted in a wrong manner or does not have enough blood on the strip for reliable reporting of blood glucose values

[0036] 5. As opposed to all other glucometers the detection of glucose is not in whole blood, but is in plasma

[0037] SOPStandard Operating Procedure

[0038] 1. Wash hands with warm water & soap and dry them well before you start testing.

[0039] 2. Take a strip from the container. Close the container again immediately

[0040] 3. Insert a new lancet into the lancet holder. Lancet must audibly click into place

[0041] 4. Press the priming button as far as it will go. The device is primed when a yellow dot appears in the middle of the release button

[0042] 5. Prick finger with the lancet provided after wiping with an alcohol swab

[0043] 6. Apply the drop of blood to the centre of the orange field on the strip & put aside

[0044] 7. Turn on the machine; wait for the prompt INSERT STRIP

[0045] 8. Wipe off excess blood, if any, with tissue. On seeing the prompt, insert strip in the slot provided with blood drop side being the lower side.

[0046] 9. Wait for the glucose reading to appear on the screen. The readings get saved automatically

[0047] 10. Turn off the machine after use to conserve battery.

[0048] Precautions:

[0049] 1. Do not use your test strips after the expiry date printed on the container. Discard them in a regular trash can.

[0050] 2. Dispose off used lancets so that the needles cannot cause inadvertent injury.

[0051] Comparison with standard liquid assay for plasma glucose:

[0052] The accuracy of the developed test is comparable to other glucose concentration analyzing instruments available in market and is in compliance with ISO 15197 with more than 95% readings with +/20% of the reference test. N=257; r.sup.2=0.88.