WO2007125272A1

WO2007125272A1 - An indicator element for detecting the presence of a target substance in a fluid

Info

Publication number: WO2007125272A1
Application number: PCT/GB2007/001403
Authority: WO
Inventors: Richard Morgan; Daniel Stanley Thomas Pratley
Original assignee: Innovation Medical Ltd.
Priority date: 2006-04-28
Filing date: 2007-04-18
Publication date: 2007-11-08
Also published as: GB2451394B; GB0608434D0; GB0821281D0; GB2451394A

Abstract

An indicator element (110), and methods for the making of such an indicator element, for providing a visual indication of the presence or absence of a substance in a fluid, comprising a carrier and a reagent carried by the carrier, the reagent being distributed over the surface and/or within the body of the carrier in such a way that a visually discernible change (150,160,170) to the indicator element occurs upon reaction of the reagent with one or more target substance.

Description

AN INDICATOR ELEMENT FOR DETECTING THE PRESENCE OF A

TARGET SUBSTANCE IN A FLUID

This invention relates generally to indicators for detecting the presence of a target substance in a fluid, and is particularly, though not exclusively, concerned with indicators for detecting and indicating the presence of glucose in urine. By the same token, if an indicator element is used to conduct a test and it does not show the presence of the target substance, then the absence of the target substance can be inferred.

hi the medical profession, the diagnosis of diseases, infections, ailments or the like in humans is generally performed by a suitably qualified and professionally trained medical practitioner, such as a doctor. Typically an individual to be diagnosed is required to visit a medical practitioner's surgery or a hospital for the diagnosis to be carried out. Diagnostic procedures can be distressing to the patient, particularly when the disease is of a serious nature, and especially if the patient was previously unaware of the existence of the disease. Such procedures can also be time consuming to perform and may be uncomfortable for the patient. Additionally, they may often entail a substantial delay before the patient receives the results. Unfortunately, the diagnosis of diseases or infections often does not occur until the disease has reached a relatively advanced stage and therefore may be unbeatable, hi such circumstances the quality of life of the patient may be affected or it may

even be fatal. There is a general need to be able to test for a medical condition in an individual before the condition reaches an advanced or serious stage which may not be treatable or curable.

The present invention seeks to provide a cost-effective method of providing a preliminary indication to an individual of the existence of a medical condition before diagnosis by a medical practitioner is performed or is even needed and which is easily undertaken in a routine manner by the individual himself or herself.

Such preliminary indication is known as screening. Screening and diagnosis are different. Screening implies the detection of the presence of a disease or condition before discernable symptoms appear. For that reason it is generally carried out on a public health scale involving the whole population, or a targeted sector of it (e.g. breast cancer screening in women over a certain age). There is currently no screening programme for diabetes in the UK, although most health authorities agree that up to 3% of the population has diabetes without knowing it, and that when the diagnosis is finally made, up to half have already developed what would have been preventable complications involving blood vessels of the eyes and kidneys. To be worth screening, a condition must normally be treatable or its progression preventable. Diagnosis, on the other hand, is a more definitive process of establishing a condition or illness, for example the underlying cause of a symptom or sign once present, or the confirmation of a possible positive identification resulting from a public-wide screening process. A major benefit of screening is that it may advantageously provide an individual with an early indication of the possible or probable existence of a medical condition or the onset of a medical condition, allowing the individual to consult a medical practitioner for a further opinion and diagnosis.

The following products for, and methods of, screening for diabetes are known.

US3,713,772 discloses the use of reagents in the form of a liquid, powder or tablet which may be supplied to the pan of a toilet, and which mix with urine and may exhibit a colour change, which, if it happens, provides an indication of the presence of glucose in the urine.

JPl 1172739 discloses a cleaning liquid containing reagents, which is introduced into the cistern of a toilet and flushed from there into a toilet pan where it may change the colour of the liquid to indicate the presence of glucose in urine.

JP61165663 discloses a moulded tablet comprising a reagent and a water-soluble carrier which may be introduced into a toilet pan. As the tablet dissolves in the liquid in the pan the reagents mix with urine and, if glucose is present, will change its colour to indicate the presence of glucose.

JP 8262010 discloses a reagents carrier. One of the reagents may test for the presence of glucose in urine, while another may test for the presence of blood and another for the pH of the liquid into which the carrier is introduced. Changes in colour of the reagents on the carrier are compared with a colour sample chart to indicate the relationship between concentration and colour and thus provide an indication of the presence of glucose or blood etc. in urine.

One problem with this latter arrangement is that it is difficult to compare the colour of the reagents on the colour sample with the colour of the carrier in the toilet pan, especially because the carrier may sink to the bottom of the pan. Additionally, it is unpleasant for a person to have to bend over a toilet pan and compare the colours of the reagents on the carrier with a supplied colour chart.

Other disadvantages of the prior art systems are that if the reagents are stored in the cistern there is no way of choosing when to use them. In other words, every time the toilet is flushed the reagents will pass into the pan. Since toilets are used by more than one person, if a user did not wish or need to take advantage of the screening the reagents are wasted. Further, there is a risk of deterioration of the reagents over time when stored in the damp environment of a toilet cistern.

With regard to the products which are added to the toilet pan and dissolve therein (known as "liquid phase technology") with a colour change of the liquid providing an indication of the presence of glucose in urine, another problem is that the colour may only change subtly leading to difficulty for a person correctly to identify the results. There is also the issue of dilution. Where a toilet pan may hold several litres of water, large quantities of reagent must be added to achieve adequate concentration. This can cause be both practically and financially prohibitive. Further still, if the user is colour-blind it may be virtually impossible for them to identify the relevant colour change. Yet further, if the lighting conditions in the room where the toilet is located are inadequate, it will be difficult for a person clearly to identify the results of the reaction. Finally, if other objects are present in the toilet pan, such as toilet paper, they may also cause problems for the person attempting to identify any colour change in the liquid.

The present invention seeks to provide a different approach to this problem, making it possible visually to indicate the presence or absence of a given substance in a fluid remotely. In other words, a person wishing to determine the presence or absence of a give substance does not have to come into contact with the fluid and thus avoids possible contamination either from, or of, the fluid (for example urine).

In one aspect, the invention provides an indicator element for providing a visual indication of the presence or absence of a substance in a fluid, comprising a carrier and a reagent carried by the carrier, the reagent being distributed over the surface and/or within the body of the carrier in such a way that a visually discernible change to the indicator element occurs upon reaction of the reagent with one or more target substance.

Although the above description has been concerned with urine and toilets, it should be understood that the indicator may be used with any type of fluid, not necessarily a bodily fluid, and may provide an indication for the presence or absence of any one or more of a wide range of substances in that fluid. For instance, such an indicator may be used with a sample of river water to detect the presence of contaminants such as heavy metals, possibly due to industrial pollution. Further, the indicator could be used to provide a visual indication of the absence of dissolved oxygen in water. The absence of such dissolved oxygen in water is, of course, dangerous for aquatic life such as fish. The invention may also be employed to indicate pregnancy from the hormonal changes in the urine that occurs early after conception. Alternatively, or additionally, the invention may be employed to determine the presence of a medical condition detectable by the reaction of reagents to constituents of, or substances in, other bodily fluids, such as saliva and semen, for such conditions as sexually transmitted diseases or as an indication of the presence of drags or state of intoxication.

The visual indication may be provided by the reagent in the form of a visually discernible pattern on and/or in the carrier. This pattern may be regular or substantially random, and it provides a clear indication of a result. Visual indication does not rely on comparison of colour with a chart. The carrier may be blank, translucent or transparent prior to use. Alternatively it may have an initial pattern which then clearly changes upon reaction with the target substance. The visually discernible pattern may be a variation of colour or hue, shade, or strength of colour. The pattern may be in the form of at least one visible and recognisable indicium, such as a letter or number on and/or in the carrier or in some other easily recognised and meaningful form. Further, the carrier may include more than one reagent so that it may simultaneously provide a visual indication of the presence or absence of more than one substance in a fluid. For instance, the indicator may be such that if the presence or absence of one substance is detected one letter or number appears on or in the carrier and if the presence or absence of another substance in the fluid is detected, a different letter or number appears on, or in, the carrier. These letters or numbers may be provided by the distribution of the reagent within the carrier. Alternatively, the reagent may be present in different concentrations at different locations such that not only the mere presence of a substance in a fluid may be indicated but also its concentration. For instance, the number one may appear on, or in, the carrier at one strength and the number two may appear on, or in, the carrier if a higher concentration or strength of the substance is detected in the fluid.

Another visual indication of the presence of a target substance may be provided by the reagent causing a physical change in the carrier. For instance, the carrier may de-laminate into two or more essentially planar elements or parts. Alternatively, the carrier may break apart into several discrete fragments (for instance it may break into quarters). Further, a central portion may dissolve or separate from an outer portion leaving behind an annulus. A yet further possibility is that the visual indication is provided by effervescence.

It is possible for the reagents to be held in a matrix provided by the carrier. The reagents may be held within the matrix homogenously or discretely. Any chemical reaction occurring as a result of the indicator being used may take place within or on the matrix. The carrier may prevent dilution of the reagent within the fluid being tested. Also, it is possible that the fluid being tested may be absorbed into the matrix, rather than the reagent dissolving out of the matrix into the fluid. The reagent may be absorbed so that it remains substantially close to the surface of the carrier. For example, it may be undesirable to allow the reagent to dissolve out into a toilet pan where the environment would not be standardised (for example the pH may be at an undesirable level). Of course, it is possible for both the reagent to dissolve out and for the fluid to be absorbed into the matrix simultaneously either in response to the presence of different substances or as different reactions to the same substance. Any reaction within the matrix may be described as taking place in a controlled environment. The matrix and reagent are known as "solid phase technology". The reagent may be adsorbed onto the surface of the constituent material comprising the matrix. Further, the matrix may comprise a porous material, for example collagen, in that it includes interlinked voids. The reagent may be adsorbed onto the surface of the material surrounding these voids substantially within and inside the body of the matrix. This adsorption may improve the permanence of the reagent in and/or on the matrix in that the removal or loss of the reagent from the matrix due to mechanical or chemical action would be diminished.

It may be desirable to ensure that the indicator floats at or near the surface of the liquid to be tested. For example, it is known that urine tends to be at a higher concentration close to the surface of the water in a toilet pan, and therefore it is desirable to have the indicator in this region of concentrated urine rather than allowing it to sink to the bottom. Accordingly, it may be desirable to select the density and/or the shape of the carrier to permit it to float at or near the surface of a liquid. For instance, if the carrier is formed as a hollow body it will float. Alternatively, a chosen low-density material or a foam material may be included in the carrier to reduce its overall density.

The carrier may include buoyancy means to permit it to float at or near the surface of a liquid. Such buoyancy means may comprise at least one void in the carrier filled with a gas. This gas may include oxygen, and may be a bubble of air or of pure oxygen. A plurality of gas bubbles may be arranged in a particular pattern in the carrier so that the carrier floats in a particular orientation in the liquid.

In one embodiment, the indicator may be substantially in the form of a disc. In such an embodiment, the buoyancy means may be arranged to provide asymmetric buoyancy so that in use a given face always lies uppermost and parallel to the surface of the liquid. This may be achieved by arranging the gas bubbles substantially in a circle in a plane parallel to a major face of the disc. Alternatively, relatively small bubbles may be distributed homogenously throughout the disc.

The carrier may be manufactured from a biodegradable material such as agar, gelatine, or glycerol. Further, the carrier may be made from a material which is soluble in water, again such as agar, gelatine or glycerol. However, with regard to the solubility of the carrier, it is of course important that the carrier does not dissolve too quickly so that the chemical reaction between the reagents and the target substance in the liquid, for which the test is being conducted, has time to take place. Further, the carrier should not dissolve too quickly because a person interested in the results of the chemical reaction will need sufficient time to observe the changes occurring.

In an embodiment in which the reagent is one which indicates the presence of glucose in urine, it is expected that the chemical reaction between the reagent and the glucose will occur within 60 seconds and accordingly, the carrier should be so formed that if manufactured from water soluble material, it does not dissolve in less time than this. The use of the word "presence" should be taken, with respect to all embodiments of this invention, as meaning not only the opposite of absence but also presence in a concentration above a pre-determined threshold level.

The device may have means for visually indicating the concentration of a target substance in a fluid. These means may result in different visually discernible patterns on or within the carrier, depending on the concentration of the substance in the fluid. For instance, one particular pattern, possibly in the form of a number or letter, may appear if the concentration is within one range, and another pattern may appear if the concentration is within another range.

In another aspect, the invention provides a method of making an indicator element for providing a visually discernible indication of the presence of a target substance in a fluid, comprising the steps of heating a quantity of gelatine; introducing at least one bubble of gas into the heated gelatine; allowing the gelatine to cool; agitating the gelatine while cooling to disperse the at least one bubble of gas into finer bubbles; cutting the cooled gelatine into an element of selected shape and size; selecting a reagent suitable for the intended purpose; and applying or introducing the selected reagent to the gelatine.

The reagent, or a solution thereof, may be applied to the surface of the gelatine element or it may be introduced into the body of the gelatine element, for example, by injection. If applied to the surface of the gelatine element, the reagent may simply be sprayed, painted or dabbed on. The application of the reagent to the gelatine may be carried out so that a pre-determined pattern of discrete amounts of reagent is produced. The reagent may be absorbed into the element. The bubble of gas may include oxygen or air.

In yet another aspect, the invention provides a method of making an indicator element for providing a visual indication of the presence of a target substance in a fluid, comprising the steps of : dissolving a quantity of agar in water; adding the selected reagent to the agar/water solution to form a mixture; pouring the resultant mixture into a mould; allowing the resultant mixture to gel; and introducing at least one bubble of gas (which may include oxygen or air) to the mixture during or after gelling thereof.

Other methods of manufacture are, of course, possible. One way of introducing the at least one bubble of gas to the mixture is to inject it after the mixture has at least partly set. Alternatively foaming agents may be added to the mixture whilst still in its liquid state and before it gels.

In one embodiment, the invention may bring the test fluid into contact with micro- quantities of reagent on an absorbent solid phase carrier, which is water soluble, rapidly biodegradable and eco-friendly. The carrier may contain fine air bubbles. The carrier may absorb the test fluid into its matrix, where the reagents may be located. The water-solubility may enhance the carrier's bio-degradability. The air bubbles may aid the oxygen-dependent reaction which generates the colour change once the fluid meets the reagents.

Any combination of the features described with reference to the various aspects and embodiments included herein are contemplated.

The present invention and its advantages will be better understood from the following detailed description in which reference is made to and the attached Figures, in which:

- Figure 1 is a perspective view of a first embodiment of an indicator prior to

use;

- Figure 2 is a perspective view of the indicator of Figure 1 in use and exhibiting a positive result;

- Figure 3 is a perspective view of a second embodiment of the indicator

before use; - Figure 4 is a plan view of the embodiment of Figure 3;

- Figure 5 is the same view as Figure 4 showing the indicator exhibiting a positive result after use;

- Figure 6 is a side view of the second embodiment of the indicator in one phase of its use;

Figure 7 is an alternative side view of the second embodiment of the indicator in another phase of its use;

- Figure 8 is a plan view of a third embodiment of the indicator before use;

- Figure 9 is the same view as Figure 8 showing indicator exhibiting a positive result after use of the indicator;

Figure 10 is a plan view of a fourth embodiment showing the indicator exhibiting a positive result;

Figure 11 is a plan view of two indicators according to a fifth embodiment showing the indicator exhibiting a positive result; - Figure 12 is a side view of a sixth embodiment showing the indicator exhibiting a positive result;

Figure 13 is a side view of a seventh embodiment, showing the indicator exhibiting a positive result;

Figure 14 is a plan view of an eighth embodiment, showing the indicator exhibiting a positive result;

- Figure 15 is perspective view of a ninth embodiment of an indicator showing the indicator exhibiting a positive result;

- Figure 16 is a side view of a tenth embodiment of the indicator in one phase of use; - Figure 17 is a side view of a first embodiment of the indicator in use in a container; and

- Figure 18 is a plan view of an eleventh embodiment of an indicator.

In a first embodiment, the indicator 10 is manufactured from gelatine by heating a quantity thereof and introducing air bubbles by any of the techniques described above. The air bubbles may, for example be introduced by blowing air into the heated gelatine. The gelatine is then allowed to cool. While cooling, the gelatine is vigorously shaken so that the air bubbles break apart into finer air bubbles 20 which then become randomly dispersed throughout the gelatine. When the gelatine has cooled, it is cut into a number of elements of selected size and shape. For example, the gelatine could be cut into discs as shown in Figure 1. One such disc has a diameter in the range 3-5cm and a thickness in the range of 2-5mm. Finally, a selected reagent, or solution thereof, is applied to the surface of the gelatine in the form of relatively small spots 30. For instance, each spot 30 is approximately 3mm across and may be added to only one or to both sides of the disc. The reagent, or solution thereof, is then absorbed into the disc due to the absorbent nature of the gelatine.

The reagent is selected for the intended purpose of its indicator. For instance, if the indicator is to be used for visually indicating the presence of glucose in urine, and therefore to signify a high probability of diabetes, the reagent needs to comprise two enzymes and a colour agent. Examples of suitable enzymes are glucose oxidase and peroxidase such as horseradish peroxidase. Examples of colour agents are orthotolodine and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) diaramonium salt (also known as "ABTS"). This reagent has no colour and is clear when applied to the surface of the disc. Accordingly, before the disc is used it has a plain undifferentiated appearance as shown in Figure 1. After use, if glucose has been detected in the test fluid (i.e. the urine) the spots of reagent will change colour, in this case to Prussian Blue, such that a distinct pattern, which matches that of the spots of reagent, is formed on the surface of the disc, as shown in Figure 2.

For the indicator to work correctly, the reagent has to be brought into contact with the fluid to be tested. This may be achieved by placing the disc into the pan of a toilet prior to urination. Alternatively, the disc could be put in after urination. Another possibility is that the disc is held in the urine stream while urinating.

If the indicator is to be used for providing a visual indication of the presence or absence of other target substances in fluids, then another reagent which reacts with the target substance to provide a visually discernible reaction will be chosen.

For the reagent to react with the glucose in the urine, in the case of diabetes screening, oxygen must also be present. One way that this may be achieved is by ensuring that the disc floats at or near the surface so that the reagent may also come into contact with the atmosphere. However, adequate contact with atmospheric oxygen is uncertain, and therefore the air bubbles dispersed within the matrix may provide some, or all, of the necessary oxygen. Although gelatine is fairly lightweight, it will nevertheless sink in water and therefore it is necessary to provide a means of flotation. Such flotation means, in one embodiment, comprise the air bubbles dispersed within the disc. However, other means of providing buoyancy are of course possible such as the inclusion of low-density material (such as wood pulp).

Although the above embodiment has been described as a disc of gelatine, other materials are of course possible. However, it is useful for the carrier to be soluble in water so that it can easily be flushed away. It is also useful if the carrier is biodegradable and non-toxic. Accordingly, materials such as gelatine and agar are preferred. However, it is anticipated that carriers made from other materials such as vegetable matter, could also be used.

In a second embodiment, the indicator 110 is made by dissolving a quantity of agar in water to form a solution and adding a selected reagent to this solution. This mixture solution is then stirred so that the reagent is uniformly dispersed throughout the agar/water solution. The mixture is then poured into moulds and shaped to produce the resultant indicator disc. Finally, at least one bubble of gas 140 is then introduced into the resultant indicator.

The gas in question could be normal atmospheric air. Figure 3 is a perspective view of an agar disc 110 having eight bubbles of air 140 uniformly distributed around the circumference, close to the perimeter, of the disc. These bubbles have been introduced into the agar disc by injection in a pattern, as shown in Figure 4. The arrangement of bubbles 140 provides buoyancy to the disc so that when placed in water the disc will float. If there are enough bubbles present the disc will float at or near the surface. However, it is not essential for the disc to float, since in some situations the greatest concentration of the target substance, the presence of which is being detected, may not be at the surface of the liquid.

Further, if the oxygen is required for the reaction to occur, this may be provided by the air in the bubbles within the disc and therefore the disc does not have to be at the surface. Accordingly, the air bubbles may be present merely for facilitating the chemical reaction and not to provide buoyancy.

The presence of the air bubbles in the reagent/agar/water mixture ensures that the reaction occurs more readily adjacent the air bubbles. This reaction decreases in intensity with distance away from the air bubbles. The reaction of the above - identified reagent produces a colour change in the disc to produce dark blue or purple patches 150 adjacent each air bubble 140. The intensity of colour fades gradually with increasing distance from the air bubble.

Since the disc 110 carries several air bubbles 140 it is possible for the colour change to overlap to provide areas 170 of darker colour at a greater distance from the air bubbles, hi Figure 5, an example of this is shown. The disc 110 has air bubbles 140 in a circle close to the circumference of the disc. The colour change due to the positive reaction of the reagent with glucose is strongest in the region 150 near to each air bubble 140 and fades away to the region 160 at distance from the air bubbles. However, where the colour overlaps in the region 170 it is stronger again. Accordingly, a pattern is produced in the disc. This pattern provides a very clear indication of a positive result, for example, that glucose has been identified in the test fluid. This pattern is clearly visible even to colour blind people.

Figure 6 shows a disc of the second embodiment floating on the surface of a liquid 80. On the other hand, Figure 7 shows the disc of this embodiment slightly below the surface of the liquid 80.

Although this embodiment has been described with several air bubbles, it is of course possible that there may be only one air bubble provided in the disc 110. An example of such a disc is shown in Figure 8 where one air bubble 140 is provided in the centre of the disc 110. The patterns appearing on such a disc indicating the presence of a target substance (that is a substance to which the reagent reacts) in the region is shown in Figure 9. In this figure it is seen that the colour is strongest or darkest 150 closest to the air bubble 140. This colour then fades in the region 160 at distance from the air bubble.

Another pattern which it is possible to produce on, or in, an indicator is shown in Figure 10. hi this third embodiment, a number 1 appears either on the surface or within the body of the disc 210 to indicate a positive result. If this number is to appear on the surface of the disc then the reagent is merely applied to the surface in the shape of the number required. However, if it is to appear within the carrier then either air bubbles would have to be introduced into the interior of a disc made from a water/agar/reagent mixture in a particular pattern, or the reagent would have to be introduced into the body of gelatine in the particular pattern.

Figure 11 shows two discs each exhibiting a different pattern. The disc 310A exhibits a tick 320, while disc 310B exhibits a cross 322. Such visual indications could be used to provide an indication of the presence or absence of a substance in a fluid, in other words the tick could be used to indicate the presence and the cross to indicate the absence. For this, reagents reacting with glucose or other target substances would be applied in the pattern of the cross, while reagents which react to water or urine in the absence of glucose would be applied in the pattern of the tick.

Although patterns have been discussed as providing an indication of the presence or absence of a target substance in a fluid, it is possible to provide visual indications in other ways. For instance, the disc 410 could be made to effervesce producing a host of bubbles 420 such as is shown in Figure 12.

Another possibility is that the disc 510 could be made to de-laminate into two thinner discs 515, 516. An example of this is shown in Figure 13.

Yet another alternative is that the disc 610 could break into parts 615, 616, 617, 618, as is shown in Figure 14. The de-lamination and/or the separation apart of the disc into smaller fragments can be achieved by means of reagents located within the disc, which have been carefully selected such that upon activation, due to the presence (or absence) of a target substance in the fluid, dissolve more quickly than the body of the carrier.

Another example of this is shown in Figure 15 in which the disc 710 is arranged so that the centre 716 drops out or dissolves more quickly than the outer annulus 715.

If it is desired that the indicator floats on the surface of a liquid it could be formed in concave shape 810 as shown in Figure 16.

hi one embodiment, the indicators could be used to indicate the presence (or absence) of a target substance in a liquid other than a bodily liquid, such as river water. In this case, the user may place some of the liquid to be tested into a container 90 before placing the indicator 10 into it. An example of this is shown in Figure 17.

Another embodiment of the present invention is shown in Figure 18. hi this embodiment, different strengths of the reagent are provided in different areas within, or on, the surface of the disc such that they may provide an indication of the concentration of a substance in a liquid. For instance, if the amount of glucose in the urine is low then only the word "low" 915 will appear, in, or on, the disc. However, if the concentration is of medium strength then the word "med" 916 together with the word "low" 915 will appear in, or on, the disc. Finally, if the concentration is high then the word "high" 917 together with the words "med" 916 and "low" 915 will appear. Although the shape of the indicator has been described as a disc, other shapes are of course possible. Further, it may be useful to have different shapes for different purposes. In other words, a disc could be used for the identification of glucose in urine, while a square could be used for identifying the presence of blood in urine and a diamond for indicating pregnancy.

It is also possible to use indicators of different size and shape to provide a greater target area to which the fluid may be applied. Further, a plurality of individual indicators could be used substantially to cover the surface of the water in a toilet pan to ensure that the urine contacts at least some of the indicators. The indicators could take the form of balls, beads or granules either coated and/or impregnated with a pre-determined reagent. Alternatively, the indicator could be substantially rectangular in shape, but relatively thin, which in use lies on the surface of the water in a toilet pan and extends across substantially the entire area, at least from front to back. Alternatively, or additionally, the size of the indicator could be varied to increase the target area.

Claims

1. An indicator element for providing a visual indication of the presence or absence of a substance in a fluid, comprising a carrier and a reagent carried by the carrier, the reagent being distributed over the surface and/or within the body of the carrier in such a way that a visually discernible change to the indicator element occurs upon reaction of the reagent with one or more target substance.

2. An indicator element according to claim 1, wherein the reagent provides the visually discernible change in the form of a visually discernible pattern on and/or in the carrier.

3. An indicator element according to claim 2, wherein the said pattern is in the form of a recognisable indicium, letter or number on and/or in the carrier.

4. An indicator element according to claim 1, wherein the visually discernible change comprises separation of the carrier into fragments.

5. An indicator element according to claim 1, wherein the visually discernible change is delamination of the carrier.

6. An indicator element according to claim 1, wherein the visually discernible change comprises effervescence.

7. An indicator element according to any preceding claim wherein the density and/or shape of the carrier are chosen such that it floats at or near the surface of a liquid.

8. An indicator element according to any of claims 1 to 6, wherein the carrier includes buoyancy means to permit it to float at or near the surface of a liquid.

9. An indicator according to claim 8, wherein the buoyancy means comprises at least one gas bubble.

10. An indicator according to claim 9, wherein the at least one gas bubble comprises or includes oxygen.

11. An indicator element according to any of claims 8 to 10, wherein the buoyancy means are so arranged that the carrier floats in a predetermined orientation.

12. An indicator element according to claim 11, when dependent on either of claims 9 or 10, wherein the gas bubbles are arranged substantially in a circle in a plane parallel to a major surface of the carrier.

13. An indicator element according to any preceding claim, wherein the carrier

is biodegradable.

14. An indicator element according to any preceding claim, wherein the carrier is soluble in water.

15. An indicator element according to any preceding claim, wherein the carrier is absorbent.

16. An indicator element according to any preceding claim, wherein the carrier is comprised entirely or largely of glycerol.

17. An indicator element according to any preceding claim, wherein the carrier is composed at least partly of agar.

18. An indicator element according to any preceding claim, wherein the carrier is composed at least partly of gelatine.

19. An indicator element according to any preceding claim, wherein the target substance is glucose and the reagent comprises glucose oxidase or peroxidase, and orthotolodine or ABTS.

20. An indicator element according to any preceding claim in which the reagent is so disposed as to be able to provide a visual indication of the concentration of a target substance in a fluid.

21. An indicator according to claim 20, wherein the said visual indication of the concentration is provided by a visually discernible pattern the shape, form or shade of colour of which depends on the concentration of the target substance in the fluid.

22. A method of making an indicator element for providing a visually discernible indication of the presence of a target substance in a fluid, comprising the steps of :

a. heating a quantity of gelatine; b. introducing at least one bubble of gas into the heated gelatine; c. allowing the gelatine to cool; d. agitating the gelatine while cooling to disperse the at least one bubble of gas into finer bubbles; e. cutting the cooled gelatine into an element of selected shape and size; f. selecting a reagent suitable for the intended purpose; and g. applying or introducing the selected reagent to the gelatine.

23. A method according to claim 22, wherein the at least one bubble of gas is oxygen or air.

24. A method according to either of claims 22 and 23, wherein the reagent is applied to the surface of the gelatine element.

25. A method according to claims 24, wherein the reagent is absorbed into the gelatine.

26. A method according to any of claims 22 to 25, wherein the reagent is applied or introduced to the gelatine element in a discrete pattern.

27. A method of making an indicator element for providing a visual indication of the presence of a target substance in a fluid, comprising the steps of :

a. dissolving a quantity of agar in water; b. adding the selected reagent to the agar/water solution to form a mixture; c. pouring the resultant mixture into a mould; d. allowing the resultant mixture to gel; and e. introducing at least one bubble of gas to the mixture during or after gelling thereof.

28. A method according to claim 27, wherein the said at least one bubble of gas is injected into the cooled or cooling mixture.