CA1131107A

CA1131107A - Color stable glucose test

Info

Publication number: CA1131107A
Application number: CA341,245A
Authority: CA
Inventors: Bert Walter
Original assignee: Miles Laboratories Inc
Current assignee: Bayer Corp
Priority date: 1979-02-23
Filing date: 1979-12-05
Publication date: 1982-09-07
Also published as: DE2951221C2; ATA100080A; IL58921A0; IT1126878B; GB2045427B; AU5580780A; DK78980A; FR2449727B1; NL7909224A; JPS5729160B2; IL58921A; GB2045427A; JPS55120798A; FR2449727A1; DE2951221A1; AT368190B; IT8047555A0; FI800181A; US4273868A; AU521192B2

Abstract

Docket No. 11899 COLOR STABLE GLUCOSE TEST
ABSTRACT OF THE DISCLOSURE
Test means, such as a composition, a test device, method of making the test device and process for determining glucose in a body fluid sample are disclosed. More par-ticularly, the contemplated test means comprises glucose oxidase, a peroxidatively active substance, such as per-oxidase, and a 3,3',5,5'-tetraalkylbenzidine indicator in an amount sufficient rapidly to produce upon contact of the test means with a predetermined amount of a glucose containing sample, a stable colored reaction product. The preferred benzidine indicator is 3,3',5,5'-tetramethylbenzidine.

Description

, 1~LD OF T~IF IN~L~

Thi prescnt i.nvention rel~tcs gcllcl-ally to the iield of diagnostic tests and, more particularly, to those tests USt'~ (lu~litative and quanti-tative determi.nation of ~lucose in whic}l tcsts glucose is converted to a peroxide.

BACKGr~OUND OF THE lNVENTION

Clucose oxidase enzymatically con-verts glucose to glllcollic acid and hydrogen peroxide. The hydrogen peroxide thus formecl can be reduced to l-l20 by a peroxidative].y activc substance in the presence of an indicator system which :is ox;d.ized to produce a response, such as a color change. ~`hc chromo~enic indicator o-tolidine has been used for some time in g]ucose test systems, but provides results which are suhjcct to reduction of the oxidized indicator by inter-fering substances, such as ascorbic acid. Further, the safety of o-tolidine has been questioned.
~ritish published patent specifications 1,464,359 and 1,464,360 which disclose the use of 3,3',5,5' tetramethyl-benzidine and similar compounds and the:ir use in the detec-tion and determination of hydrogen peroxide or of constituents which react to form peroxides. Concentrations of the benzidine derivatives disclosed therein are inconsistent and are generally not more than about 6 milligrams/milliliter.of impregnating solution uscd.
The use of the benzidine derivatives at the concen-trations disclosed in the aforementioned British published specifications results in relatively slow formation of a color or .Cormation of a color that does not remain stable over a period of time. In the :LatteI case, thc de~elope(l 113ilO7 color tends to deteriorate upon stallding, making readings suscel-tiblc to error and di.fficult or impossi~,le ~y untrained personlle I .

O~JECTS OF THE lNVENTION

lt is therefore an object of the present invention -to provide ~n improved test for the detection of glucose.
It is yet another object of the i.nvention to provide an improved tcst for glucose using materials which are recog-nized for their safety.
A further object of the invention is to provide an improved test for the detection of glucose which forms a color that remains stable over time.
A still further object of the invention is to provide an improved test for the detection of glucose in a sample wherein the above-identified advantages are achieved through a novel test means comprising glucose oxidase, a peroxida-tively active substance and a 3,3',5,5'-tetraalkylbenzidine indicator, the latter being present in an amount sufficient rapidly to produce, upon contact of the test means with a predetermined amount of a glucose-containing sample, a stable colored reaction product.

11~1107 BI~ F DE,5'C~ll'TION (~Z' TIIE DR~IWIN~;S
. ~

(!tl~er objects an~l a fuller understanding of the inven-tion l~ill be had by rcferring to the following description and claims drawn to prcferred embodiments thereof, taken in conjunction with the accompanying drawings in which:
lig. I is a graphical represcntation of the data reported in Table I using glucose test devices produced with the use oi impregnating solution formula I of Example l, such representation being obtained by plotting K/S, defir~d in.fra, vs glucose concentration;
Fig. 2 is a graphical representation of the data repolte~ in Table I using glucose test devices produced with the use of impregnating solution formula II of Example l, such representation being obtained by plotting K/S vs glucose concentration;
Fig. 3 is a graphical representation of the data reported in 'l'able I using glucose test devices produced with the use of impregnating solution formula III of Example I, such representation being obtained by plotting K/S vs glucose concentration;
Fig. 4 is a graphical representation of the data reported in Table I using glucose test devices produced with the use of impregnating solution formula IV of Example I, such representation being obtained by plotting K/S vs.
glucose concentration; and Fig. 5 is a graphical representation of the percentage of change in color observed, defined as (AK/S)/ K/S x 10(), for the test devices used to obtain the data illustrate~ in T;igs. 1-4.

S A~Y OF THL7 INV N'TLON

In contrast to prior art compositions, those o~ thc present invention are substantially free from the problem Or color deterioration. This unexpected property is observed upon incrcasing the concentration of the 3,3',5,5'-tetra-alkylbenzidille indicator. The invention therefore differs from present methology in that it rapidly provides a color which re~mains stable following its formation. One does not have to wait for the indicator color to stabilize nor be concerncd with a continuous change in color during the time after initiation of color formation. According to the inven-tion a composition and device are now available using a 3,3',5,5'-tetraalkylbenzidine rapidly to produce a stable color upon contact thereof with a sample containing glucose lS in the range of from a small but detectable amount up to at least about 400 milligrams/deciliter.
In accordance with the present invention there are provided test means, such as a composition, a test device, method of making the test device and process for determining glucose in a sample. More particularly, the contemplated test means comprises glucose oxidase, a peroxidatively active substance, such as peroxidase, and a 3,3',5,5'-tetraalkylbenzidine indicator in an amount sufficient rapidly to produce, upon contact of the test means with a predetermined amount of a glucose-containing sample, a stable colored reaction product believed to comprise reduced and oxidized forms of said indicator in stable equilibrium. The stable colored reaction product is produced within a time period of not more than about 60 seconds and, more specifically, between about 30 and 60 secon~s after contact of the test means with the body fluid sample to be tested.

1~ ~1 10'7 The concentration of 3, 3', 5, 5' tetraalkylhenzidine in relationship to the amount of glucos~ oxidase activity present in the test means of the invention is critical. In accordance with the invention the 3,3',5,5'-tetraalkyl-benzidine is present in the test means in a concentration of at least about 2.5 millimoles (mM) per thousand International Units (I.U.) of glucose oxidase activity.
l`he 3,3',5,5'-tetraalkylbenzidine compounds are parti-cularly advantageous as they have been recognized for their noncarcinogenic properties.
I.ikewise, there is provided a test device for the determination of glucose, which device comprises a carrier or matrix incorporated with the test means of the invention.
A test device can take the form of a tablet or, preferably, a device of the test strip form. Elongated sheets of carrier material which have been incorporated with the test means of the invention are contemplated as devices as used herein.
In manufacture and distribution these elongated sheets may take the form of bulk rolls, such as of filter paper material.
The device is prepared, for example, by impregnating a carrier with a solution of the test means of the invention and thereafter drying the impregnated carrier. A process for the determination of glucose in a fluid sample is provided which comprises contacting a sample with the test means or . ^
device according to the invention and observing any resul-tant color change.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although specific terms are used in the following description for the sake of clarity, these terms are in-tended to refer only to the particular embodiment of the 11;~1~07 invenlion selocted for cxem~ ry illustration, and are not intcn~ed to ~e~ine OI' limit tlle seol)e of tllc inverltion.
The test means according to t~le invention can take many physical forms and include many sl)ecific 3,3',5,5'-tetra-alkylhenzidines regardless of the form assumed. These, along with know additives such as stabi]izing agents, which caIl addit.ionally be employed if desircd, arc describc~. The test mean~ is used to detect glucose by contactin~ it with a specimen such as urine, blood, serum, cerbrospinal fluid, tissue culture supernatant or thc like.
'I'he various benzidine indicators which can be used include the 3,3~,5,5~-tetraalkylbenzidines, wherein alkyl is a (-l-C4 alkyl, and 3,3',5,5'-tetramethylbenzi~ine is parti-cularly preferred. Others which can also be used include 3-methyl, 3'-methyl, 5-ethyl, 5'-ethyl benzidine and 3,3', 5,5'--tetraethylbenzidine. ~s can be seen from these examples, the four alkyl groups can be the same or different.
Glucose enzymes which can be used are those which will ~eact with a glucose-containing fluid being tested to produce ~ predetermined reaction product, such as hydrogen peroxide. For example, glucose oxidase obtained from molds can be used. These are usually referred to as the flavo-protein type since they contain as a prosthetic group or coenzyme a flavin or isoalloxazine.
Preferably, a dual enzyme system is present: one enzyme transforms glucose to produce hydrogen peroxide, whereas the other enzyme has peroxidative activity. Sub-stances having peroxidative activity which are useful in the present invention can be chosen from various organic and inorganic sources. Plant peroxi.dases, such as horseradish peroxidase or potato peroxidase., can be used. Inorganic compounds havi.ng peroxidase activi.ty include iodides, such 113~107 as sodium and ammonium iodides, and molybdates, such as potassium and ammonium molybdates. In addition, urohemin and a number of other porphyrin substances having peroxi-dative activity can be used. Other substances which are not enzymes, but which have peroxidative activity include such compounds as iron sulfocyanate, iron tannate, ferrous ferrocyanide, potassium chromic sulfate and the like.
Since the compositions employed to measure glucose in blood, for example, should be maintained at a pH level in the range of from about pH 4 to about pH 7.5, a buffer system comprising tris(hydroxymethyl)aminomethane, malonic acid and disodium malonate is particularly useful for this purpose.
An interpolymer of methylvinyl ether and maleic anhy-dride is also useful in the formulation of glucose indi-cators of the present invention. One such interpolymer is marketed commercially as Gantrez AN-139 by GAF Corporation.
When this interpolymer is dissolved in an alcohol it forms a partial ester derivative, and when the interpolymer is dissolved in water it forms an acid derivative. Since test means prepared in accordance with the present invention are typically prepared from aqueous alcohol solutions, test compositions in the final product will contain either an acid derivative or a partial ester derivative or a mixture of said derivatives. The presence of the above described interpolymer derivatives along with polyvinyl pyrrolidone (PVP) having, for example, an average molecular weight of about 40,000, greatly enhances the color formed when color forming indicators are oxidized by hydrogen peroxide in the presence of peroxidase. This enhancement of color aids in more sharply defining different color shades for different 11;~1107 levels of ~lucose contellt in a givell fluid sample. lhis is particul~rly important to the physician in his diagnosis of the presence o~ an incipient diabetic condition.
.~lso provided are test deviccs incorporating the te~t means of the invention and a method of making such test ~evices which comprising incorporatillg a carrier with the test IllC~nS. In addition to iml~regnatioll as a-foredescrihed, incorporation of the carrier with the test means can be effected by other suitable techni(lues, such as hy printing or sl~raying the test composition onto the carrier.
}~rcferably the test device is preparcd by a process which impregnating a carrier with a first solution having from about 4 x 104 to about 8 x 104 ~nternational IJnits of glucose oxidase activity and about 22 x 105 International Units of peroxidase activity per liter and, after drying said carrier with a second solution having at least about 6 grams of 3, 3 , 5, 5 -tetraalkylbenzidine per liter for each about 1 x 104 International Units of glucose oxidase activity per liter in said first solution. The impregnated carrier is again dried after the second impregnation.
The term carrier refers to matrices which are insoluble in and maintain there structural integrity when exposed to physiological or other liquid to be tested. Suitable matrices which may be used include paper, cellulose, wood, synthetic resin fleeces, glass fiber, nonwoven and woven fabrics, gelatin, various organic polymers, such as polypropylene, and other ornanic materials well known as film formers to those skilled in the art. Alternatively, the carrier may take the form of a pressed or molded tablet containing conventional carrier material. For convenience, the carrier can be suitably attached to an insoluble support or handle memher which can be made from polystyrene.

~131107 When the tcst composition :is to be used for detecti.ng glucose i31 blood, the surace of thc impregnate~ carrier matrix is advantageously covered with a semipermeabl.e transparellt coating or film of ethyl cellulose or other suitable material. This can be accomplished by applying a layer of~ cthyl cell.ulose dissolvcd i.n benzene, for examplc, to the sllrface of the impregnated carrier matrix and then removing thc solvent by evaporative drying. A]ternati.vely, the ethyl cellulose can be part of the second impregnating solution as in the example.
(llucose tcst devices in the form of treated carrier matrices are often stored for considcrable perio~s of time hefore use, and it is therefore desirable that the reagents chosen are not easily auto-oxidizable in air. Advisably, 15 the test devices should be protected from exposure to light and in some cases it i.s desirable to keep them sealed in a moisture repellent package whi.ch is opened only for removal of one or more test devices shortly before use.
If desirable, a carrier matrix can be treated with a background dye of a particular color, such as yellow, so that the color produced by reaction with glucose is blended with the background color to produce varying tints which correspond to the concentration of glucose present in the fluid or liquid being tested. It may be especially desirable to dye the matrix yellow when the colored reaction product is blue.
Tlle test device is advantageously used by momentarily dipl)ing it in a test sample or by otherwise introducing a test sample into the carrier matrix, whereby a detectable color change results when glucose is present. The volumetric capacity of the carrier serves to limit the amount of samplc absorbcd the~eby and to which the tcst mealls incorporatc~l thercwith is exposed. ~ny excess sample can be removed by 11~110~
washing o-r blot-ting the carrier to thereby linlit the amount of ~ampl~ tcsted to the volume thereof which has actually entered the carrier m~trix. The test device can be used in the same way wllell samples of plasnla, serum or other body fluids are tested.
Reflectance readings Or color produced by rcaction with glucose present in sample can be obtained from commercially available spectrophotometers such as Beckman UK-2 Spectro-photometer, Beckman Instruments, Inc., Fullerton, California or Spectrocolorimeter SCF-l, Israel Electro-OI)tical lndustry ltd. (distributed in the U.S. by Broomer Research Corporation, Plainwell, Long Island, N.Y.).
Eor highly precise determinations of glucose concen-tration, photoelectric, colorimetric or spectrophotometric methods can be employed to determine color indication. The EYETONE~ reflectance colorimeter ~Ames Company, Division of Miles I.aboratories, Inc.) is a portable instrument designed to quantitatively measure whole blood glucose when used in conjunction with DEXTROSTIX~ reagent strips (Ames Company, Division o Miles Laboratories, Inc.). The EYETONE reflec-tance colorimeter measures the light reflected from the surface of the reacted test device matrix and converts this measurement, by means of electronic circuitry, to a reading on a precisely calibrated meter scale on the instrument which is capable of indicating blood glucose within the range of 10 to 400 milligrams (mg)/100 milliliter (ml). The higher the blood glucose level, the darker the strip and the less light reflected. Conversely, the lower the blood glucose level the lighter the strip and the more light reflected.
The colorforming test means or device described herein has hecn found to be especially useful in that it provides a 11~1107 uni(lue color response which call he (letcrlnined by the EYE'I'ONI
rerlectailc~ colorimeter in a fa~hion similar to tl~at o~
'I'RO~ reagcnt strips. Altelllatively, semiquantitative results can be obtained usin~ the glucose ;ndicator Or the present invention by comparing the co]or produced with a ~anel of standard colors obtained with known concentrations of glucose cmploying the same glucose indicator.
' 'I'he relationship between K (the absorption coefficient of the specimen) and the concentration of the absorbing species (i.e. glucose) is given by the Kubelka-Monk equation which is provided, along with a detailed discussion of reflectance spectrophotometry in Kortumi, G., ~ef~ectance sp~(?tro~opy~ Springer-Verlag Inc., New York, 1969.
The term K/S, used in the example, is a ratio that is defined by the formula (1-R)2/2R, wherein R is reflectance and ~ is the scattering coefficient of the particular carrier used. Therefore, K/S is proportional to the amount of chromogen formed by the reaction. Readings in the example were taken at the wavelengths indicated.
Horeseradish peroxidase and glucose oxidase used in the example were obtained from The Research Products Division, Miles Laboratories, Inc., Elkhart, Indiana. A copolymer of methyl vinyl ether and maleic anhydride (Gantrez AN-139) and polyvinyl pyrrolidine (PVP) were obtained from GAF Corp., Chemical Products, N.Y., N.Y.). The solvent used in pre-paring the solutions can be water, physiological solutions, organic solvents, such as methanol, or mixtures th'ereof.
The example shown is merely illustrative and is not to be construed as a limitation of the invention. One skilled in the art will be able to make such variations, substitutions and changes in the ingredients and parameters as may seem desiral~le.

Bxaml)le I

Devices were prep.lred to incorporate compositions for the quantitative determination of g].ucosc. The composition~
used in preparing the devices cach had a differcnt con-centration of the ind-icator 3,3l,5,5~ tetramethylhenzidinc (TMB). Tlle e~fect of this difference on stability over time of the color formed was examined.
A first impregnating solution was prepared to contain the fo].lowing:
(omponents Quantity _inal Concentration ..
ethanol 25 milliliter (ml) 25% volume/volume (v/v) Jl2 40.5 ml g1ucose oxidase 1 6 ml 8 x 104 IU/li.ter (5 x 10 IU/ml) horseradish - peroxidase 250 milligrams (mg) 5 ~'30.8 IU/mg) 22 x lO IU/liter citrate buffer 25 ml (1.8 M; pH 4.8) 0.36 Molar (M) Gantrez AN-139 in ~l2O 12 ml 1.2% weight/volume (w/v) tlO% w/v) PVP 300 mg 3% (w/v) A second impregnating solution was prepared for each of the TMB concentrations to be tested by adding 10, 25, 50 and 75 ~rams of TMB, respectively, to four 1.0 liter solutions of chloroform containing 17.5 grams of ethyl cellulose each.
The final concentration of TMB in these impregnating solutions was 41.9, 104, 208 and 312 millimolar (mM), respectively, and the formulae of these solutions are designated as I, II, III and IV. Thus, the relationshi.ps of the millimolar quantities of TMB in in-pregnating soluti.ons I to IV to the numhcr of International Ullits o glucose oxidase in the filst implegnating solution are 0.52, 1.30, 2.60 and 3.90 mM

11 ~1 107 pel l()l~0 I.U., respective]y. ~imi]arly, the relationsllip~
o~ th~ weig]lt of rrMB in i~pre~n;ltin~ so]lltions I to IV to the numbel of International lJl-its of glucose oxidase in the first ililpregnating solution are 0.125, 0.313, 0.625, and 0.938 gm/ lO00 I.U., respectively. All of these relation-shiI-s are shown on Table I for the respective impreKnating solutions T to IV.
~:our sheets of Laton-Dikemarl 204 (~ ~ D) filter pa~er were impregnated to saturation with the first impregnating solution and dried at 80 C. Each of the so-impregnated sheets was then impregnated to saturation in a separate one of the sccond impregnating solutions and dried at 60 C.
'I]le papers so prepared were cut to 0.5 centimeter (cm) x 1.0 cm to form test devices. l'he devices were then backcd with double-faced adhesive tape and fixed thereby to organo-plastic support members. ~ach device prepared contained approximately 1.7 I.U. of glucose oxidase, and 5.4 I.U. of peroxi~ase. The final amounts of TMB in the devices con-taining formulations l-IV were approximately O.Z2, 0.55, 1.10 and 1.6 mg, respectively.
Devices of each formulation were tested by contacting them resl)ectively with a separate one of each of four aqueous glucose solutions. The glucose concentrations in these solutions were 93, 201.9, 302.4 and 372.2 milligrams/deciliter (mg/dl) respectively. After saturation of the carrier of each device with sample the reaction was allowed to proceed for 60 seconds. Any excess sample on the device was then washed off by momentarily placing the device in a stream of running water and blotting away excess liquid using ordinary facial tissue. The device was then placed in a recording reflectance spectrophotometer and the color change was read 1~

... .. .. . . .. .. . . ... .. . . . . .. .

at 55() nanometeI-s (nm~ ~ secon~s an~ ag~in at G0 seconds after w~shing. The reflectancc values observed were con-verted to K/S v~lues ~s previously ~escribed and the resul t.s obtained are shown in Table I.

Table I

ormula I - 0.5Z mM (0.125g) TMB per 1000 I.U. of glucose oxidase (~,OD) Glucose Level K/S
(mg/~l) 20 sec. hO sec.

93 0.219 0.215 201 9 0.677 0.558 302 4 1.460 1.000 372.2 1.710 1.150 Formula I_ - 1.30 mM (0.313g) TMB per 1000 I.IJ. GOD

Glucose Level K/S
(mg/dl) 20 sec. 60 sec.
-93 0.238 0.239 201.9 0.651 0.640 302.4 1.200 1.100 372.2 1.560 1.310 Formula III - 2.60 mM (0.625g) TMB per 1000 I.U. GOD

Glucose Level K/S
(mg/dl) 20 sec. 60 sec.

93 0.278 0.283 201.9 0.630 0.634 302.4 1.170 1.160 372.2 1.550 1.530 I:ormula IV - 3.90 mM (0.938g) TMB per 1000 I.U. GOD

Glucose Level K/S
~mg/dl) 20 sec. 60 sec.

93 0.279 0.281 201.9 0.716 0.715 302.4 1.280 1.210 372.2 1.480 1.430 Figs. 1-4 graphically represent the data reported in Table I for devices containing formulations I-IV, respec-tively. The solid lines represent the K/S readings taken at 20 secorlds after washing of the dovice and the brokcn ~ine~
represent the ~/~ readings at 60 seconds. Fig. 5 graphi-cally represents the percentage of change in color o~serve~, defined as (~ K/S)/ K/S x 100), for devices containing each s of the formulations I-IV.
A stable color (blue) was visually ohserved substan-tially immediately upon removin~ the excess sample from the devices having formulations III and IV, whereas degradation of color, with resultant error in glucose levels detected, occured with the devices having formulations I and II. The devices with formulations III and IV, having higher TMB
concentrations, give a substantially immediate color end point which is stable thereafter.
Iigs. 1 and 2 show that there is a substantial change between the readings taken at 20 seconds and at 60 seconds.
These readings are proportional to the amount of chromogen formed. rhe amount of glucose reported by such dcvices is therefore totally unreliable. In contrast, the virtually identical readlngs shown in Figs. 3 and 4 demonstrate the stability of the color formed in accordance with the inven-tion. Fig. S shows a percentage of color change from the 20 second reading to the 60 second reading of over 30~
using formulation I and less than 3% using formulation III.
The present invention therefore provides a greater than 10-fold improvement over the prior art.
Although the invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made only hy way of example and that numerous changes in the details may be resorted to without departing from the scope of the invention.

]h

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A composition for the determination of glucose in a body fluid sample which comprises glucose oxidase, per-oxidase, a buffer effective to maintain a pH of from about 4 to about 7.5, a stabilizing agent and 3, 3', 5, 5' tetra-methylbenzidine, wherein the 3, 3', 5, 5' tetramethylbenzi-dine is present in a concentration of at least about 2.5 millimoles per thousand International Units of glucose oxi-dase activity.