INDICATOR

Abstract: An indicator, which is intended for detecting at least one test substance in a test medium, comprising a carrier and a reaction system consisting of at least a first reactant and a second reactant, applied separately on the carrier, said first reactant being intended to travel by diffusion to the second reactant through a path in the carrier, soaked by the test medium, while reacting with the test substance. The indicator is characterized in that the first reactant is applied within at least one limited locality, whilst the second reactant is applied within at least one locality, on a varying distance from the locality of the first reactant.

Description: » Indicator " t The present invention relates to an indicator for de¬ tecting at least one test substance in.a test medium, comprising a carrier and a reaction system, consisting of at least a first reactant and a second reactant,ap- 5 plied separately on the carrier, said first reactant being intended to travel by diffusion to the second reactant through a path in the carrier, soaked by the test medium, while reacting with the test substance. An indicator of this type is disclosed in US Pat.Appln. X0 Ser.No. 806,687, in which there is disclosed e.g. an indicator for detecting of the enzyme catalase in milk. The reaction system employed consists partly cf a first enzyme for generating hydrogen peroxide, namely glucose and the enzyme glucose oxidase, and partly of 5 a color-generating system consisting of the enzyme per- oxidase and o-tolidine, which latter is converted from a colorless state into a colored state, if it is allowed to react with hydrogen peroxide. In principle, the first, hydrogen peroxide-generating system is ap- 20 plied to a carrier in a distance to the color-gene¬ rating system. When the test shall be perfoπced, the carrier - preferably a paper strip - is soaked with the test medium, that is to say the milk. Hydrogen peroxide is evolved, which travels by diffusion in -t 25 tιe direction towards the color-generating system. On its way the hydrogen peroxide has to travel by diffu¬ sion through a part of the carrier, which is soaked by test medium. If this contains the substance sought, catalase, the latter will react with the hy- 30 drogen peroxide to an extent, that is determined by its concentration, and no or a limited quantity of the hydrogen peroxide generated can travel by diffu- 1 OMPI sion to the color-generating system to give rise to a color. The intensity of the color thus depends on the concentration of any remaining hydrogen peroxide and thus inversely on the concentration of catalase in the test caesium. This indicator may give good results, but these are de¬ pendent on a number of factors. The accuracy of the catalase determination thus demands an exact time schedule for the measuring procedure, good light and a color scale for comparison between the color develo¬ ped, and the color scale, provided with catalase con¬ centration figures at different color tinges. The co¬ lor tinge may show considerable variation depending on variations in the color of the milk itself, disturbing substances in the milk or the air, and the age of the indicator. The color tinges in the color system per- oxidase-o-tolidine may also vary with different char¬ ges in commercial production. The objective of the present invention is to provide an indicator which has none of the mentioned drawbacks. Such an indicator is characterized, according to the invention, in that the first reactant is applied with¬ in at least one limited locality, while the second re¬ actant is applied within at least one locality in a varying distance from the locality of the first reac¬ tant. By this design of the indicator the first reactant, e.g. hydrogen peroxide, will travel by diffusion along paths of different length through the carrier towards the second reactant, e.g. a color generating system like perσxida≤e-o-tolidine, and thereby be consumed to a greater or smaller extent, according to the pro- OMPI vision of test substance of the type sought in the part of the carrier, which is situated between said loca¬ lities, and which is soaked by the test medium. A lon¬ ger path of diffusion gives an opportunity for a hig- her degree of reaction between the first reactant and •the test substance, which means that a correspondingly less amount of the first reactant can reach the second reactant to form e.g. a color. It is probably most convenient to use such reaction systems, which give rise directly to a visually detectable color change, - even if other reaction systems could be considered, e.g. such systems, in which the color is only deve= loped by spraying a developer on it. Suitably the indicator is made of a plane material, like a paper sheet or the like as a carrier. In one embodiment of the indicator according to the invention the first reactant is applied as a first band on a surface of the carrier, and the second re¬ actant is applied as a second band in such a way, that the distance from the first band to the second band varies, suitably continuously. It may also be convenient to design the indicator in such a way that the first reactant is applied on one side of the carrier and the second reactant is applied on the other side. Thereby an especially good effect is obtained, if the first reactant is applied within one locality in the form of a band,oriented into a first direction, and the second reactant is applied within several localities in the form of bands, sub- stantially mutually parallel, into a direction which differs from said first direction, and is preferably perpendicular to said first direction.. In a further embodiment of the invention the first re- actant is applied onto one side of a carrier, within a locality which has a substantially circular limit, and the second reactant is applied to the other side of the carrier within localities in the form of a num¬ ber of concentric rings provided with mutual distances. In use a distinct number of rings is colored/not co¬ lored. The invention is not, per se, limited to any special mode of manufacture, but is probably quite suitable to apply the reactants by printing technique, known per se. The invention shall now be described more in detail, reference being made to the enclosed figures, of which figure 1 shows an indicator in the form of a paper strip, in longitudinal section, grossly enlarged, figure 2 shows an indicator ' , provided with reactant on one side surface, seen from above„ Figure 3 shows an indicator provided with reactants on both sides, partly perspectively, to some degree sec- tionally, and partly in use, seen from above, and figure 4 shows, in a similar way, another embodiment of an indicator with reactants on both sides. The indicator shown in figure 1 consists of a paper strip on the lower side of which there has been applied a first reactant B, in the form of a transversal band and the upper side of which is coated with reactant C. When used, the complete strip is soaked in the sample, which is to be investigated, the carrier thus being i - pregnated with test substance A. When reactant 3 is simultaneously brought into contact with the test me¬ dium, usually a liquid, the reactant, liberated from "BUREA OMPT B, starts to travel by diffusion in the direction of the arrows shown. Thereby a certain amount of the reactant will travel by diffusion straight to the upper side, whilst other amounts will have loπ- ger and longer ways of diffusion to reactant C. At a certain concentration of test substance A in the test medium, the chances for reactant A to reach reactant C will decrease, the longer diffusion way there is, as the probability for it to react with test substance A increases with increasing diffusion path. This will mean, that a relatively great con¬ centration of reactant •• will reach reactant C clo¬ sest to reactant B, and a relatively low concentration will reach reactant C further away. ' If C is a reac- tant, which will show a color directly when reacted with reactant B, this will mean a correspondingly decreasing color tinge with increased diffusion path. The indicator in figure 2 is provided with a band of reactant B and a band of reactant C, the bands form- ing an acute angle. I:. figure 2a the indicator is shown before usage, in figure 2b, when used for the analysis of a test medium with a relatively high con¬ centration of test substance A and figure 2c, when used for the analysis with relatively low concen- tration of A. The indicator, shown in figure 3 is provided, on the lower side, with reactant B applied as longitudinal bands and on the upper side with transversal bands of reactant C. Figure 3b shows the indicator when used for the analysis of a sample with a high con¬ centration of A, figure 3c for the analysis of a sample with a moderately high concentration of A, and figure 3d for the analysis of a sample with a "BUREΛ OMPI - 6 - low concentration of A. Figure 4 shows, in a corresponding way, an indicator, provided on the lower side with reactant B in the form of a small round spot, and on the upper side 5 provided with a number of concentric rings of reac¬ tant C, separated from each other. Figure 4a shows the indicator when used for the analysis of a sample with a relatively high concentration of A and figure 4c shows the indicator for the analysis of a sample 0 with a relatively low concentration of A. The indicator according to the invention has the following advantages, as compared to indicators, which have been used previously for similar purposes: 1. The sensitivity of the * indicator for a test 15 substance can be varied within wide limits, by using carriers with adapted resistance to diffusion, e.g. in the form of paper sheets of suitable thickness. 2. The color scale can be printed in black/white 20 as it is rather the color pattern than the co¬ lor tinge that determines the measuring result. 3. The reading of the indicator is simple and can be performed by non-skilled staff. 4. The reading result is relatively insensitive 25 to factors like light, color of sample, distur¬ bing components in the sample, etc. 5. The time schedule for reading of the indi¬ cator is less critical, in practical cases OMPI within an interval of some minutes. 6. The- indicator can be manufactured, advantageously, by conventional printing technique. The indicator can be used for concentration measure- ment of a number of substances, especially enzymes. In the examples shown, the first reactant is e.g. glu¬ cose, applied separated from, but in the vicinity of glucose oxidase, and the other reactant is peroxidase mixed with o-tolidine. Such an indicator can be used for the measurement of the concentration of catalase in milk. The indicator can also be used, advantageously, for the determination of other substances than enzymes. Thus an indicator for the determination of total acid concentration (expressed e.g. as m H ) can be de¬ signed according to the example just disclosed, with a reactant B consisting of an alkaline substance, like sodium hydoxide, and a reactant C consisting of a pH-indicator with a suitable detection interval, e.g. bro thymol blue for neutral pH. When soaking the indicator with test liquid, the alkaline substance will travel by diffusion through the test liquid re¬ acting with any acid available, _ and any remaining al- cali will be indicated by the reactant C. S U G OMPI

Claims: Claims 1. An indicator for detecting of at least one test substance (A) in a test medium, comprising a carrier and a reaction system, consisting of at least, one first reactant (B) and a second reactant (C) , applied separately on the carrier, the first reactant (B) be¬ ing intended to travel by diffusion to the second re¬ actant (C) through a path in the carrier, soaked by test medium, thereby reacting with test substance (A) , c h a r a c t e r i z e d i n that the first reac¬ tant (B) is applied within at least one limited loca¬ lity, whilst the second reactant (C) is applied with¬ in at least one locality, on a varying distance from the locality of the first reactant (B) . 2. An indicator according to claim 1, in which the carrier is a s tabs t ant i ally plane material, c h a - r a c t ' r i z e d i n that the reactants (B, C) are applied within localities in the form of bands on a surface of the carrier. 3. An indicator according to claim 1, in which the carrier is a substantially plane material, c h a ¬ r a c t e r i z e d i n that the first reactant (B) is applied to one of the sides of the carrier, and the second reactant (C) is applied to the other side of the carrier. 4. An indicator according to claim 3, c h a r a c ¬ t e r i z e d i n that the first reactant (3) is applied within a locality in the form of a band orien¬ ted into a first direction, and the second reactant (C) is applied within a number of localities in the form of bands, substantially mutually parallel. OMPI in a direction differing from the first direc¬ tion. 5. An indicator according to claim 3, c h r c¬ t e r i z e d i n that the first reactant (B) is applied within a locality, which has substantially circular limitation, and the second reactant is. ap¬ plied, within localities in the form of a number of concentric rings, preferably with mutual distances. 6. An indicator according to any of claims 2 to 5, c h a r a c t e r i z e d i n that at least one reactant (B, C) is applied by printing technique, known per se. OMPI

Inventors: BJOERLING KARL TORSTEN, GROENBERG ANN MARIE MAERTA SKY, GROENBERG ANN MARIE MAERTA SKYLE
Applicants: ALFA LAVAL AB, BJOERLING KARL TORSTEN, GROENBERG ANN MARIE MAERTA SKY, GROENBERG ANN MARIE MAERTA SKYLE
Application year: 1982
Main classification: G01N31
IPC codes: C12Q1, G01N31, G01N33