A sample testing device

Abstract

A sample testing device comprising at least one working electrode and a reagent dried on and / or adjacent to the surface of the working electrode. The reagent comprises a protein receptor comprising copper and / or a copper salt. The reagent further comprises an acidic buffering agent. There is also provided a sample testing device comprising at least a first working electrode and a second working electrode. A first reagent is provided on and / or adjacent to the surface of the first working electrode and a second reagent is provided on and / or adjacent to the surface of the second working electrode. The first reagent comprises a protein receptor. The second reagent comprises a creatinine receptor comprising an enzymatic receptor.

Description

[0001] A Sample Testing Device

[0002] Technical Field of the Invention

[0003] The present invention relates to a sample testing device and a test reader. In particular, the present invention relates to a sample testing device for detecting creatinine and / or a protein in a sample, and a test reader for reading / analysing the sample from the sample testing device.

[0004] Background to the Invention

[0005] Albumin is a protein synthesised in the liver before being excreted into the bloodstream. It is the most abundant protein in the plasma of a healthy human and has several functions including helping maintain oncotic pressure of blood and transporting various substances including but not limited to hormones, enzymes, and drugs such as warfarin and propranolol. Albumin blood tests may be used to determine the concentration of albumin in a patient’s blood. If the concentration of albumin is low, this may be an indication of liver or kidney disease. Alternatively, if the concentration of albumin is high, this may be an indication of dehydration. Albumin urine tests may be used to indicate a patient’s kidney function. If the kidneys are functioning correctly, most albumin is prevented from entering urine. However, if albumin is detected in urine, this may be a sign the patient has kidney disease which affects the filtering capacity of the kidney. Total protein is often used in urinalysis as a substitute for albumin and may also be used to indicate kidney disease. In a healthy human, albumin typically makes up 15% of the total protein found in urine.

[0006] Creatinine is a waste product formed naturally in the human body when muscle tissue breaks down. Creatinine blood and urine tests may be used as an indication of a patient’s renal and kidney function. Furthermore, creatinine is excreted at a relatively constant rate so may be used as an indication of urine concentration. Therefore, a sample may be tested for the presence of albumin and creatinine and the results expressed as an albumin / creatinine ratio (A:CR). Alternatively, a sample may be tested for the presence of total protein and creatinine and the results expressed as a total protein to creatinine ratio (P:CR). As albumin and total protein concentration may be affected by urine concentration which can vary throughout the day, expressing the results as an A:CR or P:CR may provide a more accurate measure of albumin or total protein concentration as the concentration of creatinine may correct for the concentration of urine when the sample is taken. As both albumin or total protein and creatinine must be measured to determine A:CR or P:CR, at least two different tests must be carried out. This may require the division of a single sample which may result in sample contamination and / or an insufficient volume of sample being collected. Alternatively, two separate samples may be collected. Given the purpose of using the A:CR or P:CR, both samples must be collected from the patient at the same time to minimise the risk of urine concentration changing during the elapsed time between sample collection.

[0007] When testing for albumin or total protein and creatinine in a sample, several different receptors may be used. However, some receptors may be affected by environmental conditions which can affect the reaction between the receptor and the sample. For example, some receptors may be particularly sensitive to significant adjustment in pH.

[0008] It is an object of the present invention to overcome these or other disadvantages and / or to provide an improved sample testing device.

[0009] Summary of the Invention

[0010] According to a first aspect of the present invention there is provided a sample testing device comprising: at least one working electrode; and a reagent dried on and / or adjacent to the surface of the working electrode; wherein the reagent comprises a protein receptor comprising copper and / or a copper salt, and an acidic buffering agent.

[0011] There may be provided a sample testing device comprising: at least one working electrode; and a reagent dried on the surface of the working electrode; wherein the reagent comprises a protein receptor comprising copper and / or a copper salt, and an acidic buffering agent.

[0012] Provision of a device according to the first aspect is particularly advantageous as it enables a sample such as urine or blood to be tested for the presence of protein. In particular, provision of the acidic buffering agent may help maintain a stable pH range, thereby improving the accuracy of measurements recorded using the or each working electrode. This is particularly advantageous when the sample testing device is used to test urine whose pH may range from pH 4-8. Furthermore, providing a reagent dried on the surface of the working electrode means no additional materials are required for the integration of the reagent such as a membrane, fabric, or filter. This may help reduce the complexity and therefore the cost of the device. The protein receptor may comprise an albumin receptor. Additionally or alternatively, the protein receptor may comprise a total protein receptor. The protein receptor may detect albumin and at least one further protein. The protein receptor may detect albumin and at least two, three, four or at least five further proteins. The protein receptor may comprise a reagent which detects albumin. The protein receptor may may comprise a reagent which detects more than one protein. The reagent may detect albumin and at least one further protein, such as at least two, three, four or five further proteins. The reagent may detect total protein.

[0013] The copper salt may be a copper (I) salt. Preferably, the copper salt may be a copper (II) salt. Preferably, the copper (II) salt may be at least one of copper sulphate (CuSCh) or copper chloride (CuCh). The copper salt may be provided in the form of copper nanoparticles.

[0014] The acidic buffering agent may confer a pKa of at least 3.0, 3.1, 3.2, 3.3, 3.4, 3.5,

[0015] 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6,

[0016] 5.7, or 5.8. The acidic buffering agent may confer a pKa no greater than 8.0, 7.9, 7.8, 7.7, 7.6,

[0017] 7.5, 7.4, 7.3, 7.2, 7.1, 7.0, 6.9, 6.8, 6.7, 6.6, 6.5, 6.4, 6.3, 6.2, 6.1, 6.0, 5.9, or 5.8. The acidic buffering agent may confer a pKa in the range of 3.0-8.0, 3.1-7.9, 3.2-7.8, 3.3-7.7, 3.4-7.6, 3.5-

[0018] 7.5, 3.6-7.4, 3.7-7.3, 3.8-7.2, 3.9-7.1, 4.0-7.0, 4.1-6.9, 4.2-6.8, 4.3-6.7, 4.4-6.6, 4.5-6.5, 4.6-

[0019] 6.4, 4.7-6.3, 4.8-6.2, 4.9-6.1, 5.0-6.0, 5.1-5.9, 5.2-5.8, 5.3-5.7, or 5.4-5.6.

[0020] The acidic buffering agent may confer a pKa in the range of 3.0-8.0, 3.0-7.5, 3.0-7.0, 3.0-6.5, 3.0-6.0, or 3.0-5.5. The acidic buffering agent may confer a pKa in the range of 3.5- 8.0, 3.5-7.5, 3.5-7.0, 3.5-6.5, 3.5-6.0, 3.5-5.5, or 3.5-5.0. The acidic buffering agent may confer a pKa in the range of 4.0-8.0, 4.0-7.5, 4.0-7.0, 4.0-6.5, 4.0-6.0, 4.0-5.5, or 4.0-5.0. The acidic buffering agent may confer a pKa in the range of 4.5-8.0, 4.5-7.5, 4.5-7.0, 4.5-6.5, 4.5-6.0, 4.5-

[0021] 5.5, or 4.5-5.0. The acidic buffering agent may confer a pKa in the range of 5.0-8.0, 5.0-7.5, 5.0-7.0, 5.0-6.5, 5.0-6.0, or 5.0-5.5. Preferably, the acidic buffering agent may confer a pKa in the range of 3.0-8.0. This may assist in maintaining the optimal pH range for the reaction between the protein receptor and a sample comprising the bio-analyte protein.

[0022] The acidic buffering agent may be at least one agent selected from the group consisting of: acidified phosphate buffer, MES buffer, sodium acetate, and any combination thereof. The acidic buffering agent may be at least one agent selected from the group consisting of: acidified phosphate buffer, MES buffer, sodium acetate, L-tartaric acid, maleic acid and any combination thereof. The protein receptor may comprise copper, which may be elemental copper. The copper may comprise copper particles which may in some embodiments be copper nanoparticles. The copper particles may comprise substantially pure copper, or may consist essentially of copper and trace amounts of one or more copper salts.

[0023] In embodiments in which the protein receptor comprises a copper salt, the ratio of copper salt to acidic buffering agent may be 4: 1. For example, the ratio of the copper salt copper chloride (CuCh) to acidic buffering agent may be 4:1. Alternatively, in embodiments in which the protein receptor comprises a copper salt, the ratio of copper salt to acidic buffering agent may be 1 : 1. For example, the ratio of the copper salt copper chloride (CuCh) to acidic buffering agent may be 1:1.

[0024] The concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be at least 130 mM, 140 mM, or at least 150 mM. The concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be no more than 170 mM, 160 mM, or no more than 150 mM. The concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be in the range of 130- 170 mM, or 140-160 mM. Preferably the concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be around 150 mM. The concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be at least 120 mM, 130 mM, 140 mM, 150 mM, 160 mM, 170 mM, 180 mM, 190 mM, 200 mM, 210 mM, 220 mM, 230 mM, 240 mM, 250 mM, 260 mM, 270 mM, 280 mM, 290 mM, 300 mM, 310 mM, 320 mM, 330 mM, 340 mM, 350 mM, 360 mM, 370 mM, 380 mM, 390 mM, 400 mM, 410 mM, 420 mM, 430 mM, 440 mM, 450 mM, 460 mM, 470 mM, 480 mM, 490 mM, 500 mM, 510 mM, 520 mM, 530 mM, 540 mM, 550 mM, 560 mM, 570 mM, 580 mM, 590 mM, 600 mM, 610 mM, 620 mM, 630 mM, 640 mM, 650 mM, 660 mM, 670 mM, 680, mM690 mM, 700 mM, 710 mM, 720 mM, 730 mM, 740 mM, 750 mM, 760 mM, 770 mM, 780 mM, 790 mM, 800 mM, 810 mM, 820 mM, 830 mM, 840 mM, 850 mM, 860 mM, 870 mM, 880 mM, 890 mM, 900 mM, 910 mM, 920 mM, 930 mM, 940 mM, 950 mM, or 960 mM. The concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be no more than 960 mM, 950 mM, 940 mM, 930 mM, 920 mM, 910 mM, 900 mM, 890 mM, 870 mM, 860 mM, 850 mM, 840 mM, 830 mM, 820 mM, 810 mM, 800 mM, 790 mM, 780 mM, 770 mM, 760 mM, 750 mM, 740 mM, 730 mM, 720 mM, 710 mM, 700 mM, 690 mM, 680 mM, 670 mM, 660 mM, 650 mM, 640 mM, 630 mM, 620 mM, 610 mM, 600 mM, 590 mM, 580 mM, 570 mM, 560 mM, 550 mM, 540 mM, 530 mM, 520 mM, 510 mM, 500 mM, 490 mM, 480 mM, 470 mM, 460 mM, 450 mM, 440 mM, 430 mM, 420 mM, 410 mM, 400 mM, 390 mM, 380 mM, 370 mM, 360 mM, 350 mM, 340 mM, 330 mM, 320 mM, 310 mM, 300 mM, 290 mM, 280 mM, 270 mM, 260 mM, 250 mM, 240 mM, 230 mM, 220 mM, 210 mM, 200 mM, 190 mM, 180 mM, 170 mM, 160 mM, 150 mM, 140 mM, 130 mM, 120 mM. The concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be in the range of 120 - 960 mM, 220-940 mM, 320-920 mM, 420-900 mM, 520-880 mM, 620-860 mM, or 720-840 mM. Preferably the concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be around 720 mM.

[0025] The concentration of acidic buffering agent in the reagent before it is dried on the surface of the working electrode may be at least 520 mM, 560 mM, or at least 600 mM. The concentration of acidic buffering agent in the reagent before is it dried on the surface of the working electrode may be no more than 680 mM, 640 mM, or no more than 600 mM. The concentration of acidic buffering agent in the reagent before is it dried on the surface of the working electrode may be in the range of 520-680 mM or 560-640 mM. Preferably the concentration of acidic buffering agent in the reagent before it is dried on the surface of the working electrode is around 600 mM. The concentration of acidic buffering agent in the reagent before it is dried on the surface of the working electrode may be at least 520 mM, 540 mM, 560 mM, 580 mM, 600 mM, 620 mM, 640 mM, 660 mM, 680 mM, 700 mM, 720 mM, 740 mM, 760 mM, 780 mM, 800 mM, 820 mM, 840 mM, 860 mM, 880 mM, 900 mM, 920 mM, 940 mM, 960 mM, 980 mM, 1000 mM. The concentration of acidic buffering agent in the reagent before is it dried on the surface of the working electrode may be no more than 1000 mM, 980 mM, 960 mM, 940 mM, 920 mM, 800 mM, 780 mM, 760 mM, 740 mM, 720 mM, 700 mM, 680 mM, 660 mM, 640 mM, 620 mM, 600 mM, 580 mM, 560 mM, 540 mM, 520 mM. The concentration of acidic buffering agent in the reagent before is it dried on the surface of the working electrode may be in the range of 520-1000 mM, 620 mM-850 mM, 720-800 mM. Preferably the concentration of acidic buffering agent in the reagent before it is dried on the surface of the working electrode is around 750 mM.

[0026] For example, the concentration of copper chloride (CuCh) in the reagent before it is dried on the surface of the working electrode may be around 150 mM and the concentration of acidic buffering agent in the reagent before it is dried on the surface of the working electrode may be around 600 mM. The concentration of the copper salt in the reagent dried on the surface of the working electrode may be at least 15 mM, 20 mM, or at least 25 mM. The concentration of the copper salt in the reagent dried on the surface of the working electrode may be no more than 35 mM, 30 mM, or no more than 25 mM. The concentration of the copper salt in the reagent dried on the surface of the working electrode may be in the range of 15-35 mM or 20-30 mM. Preferably, the concentration of the copper salt in the reagent dried on the surface of the working electrode may be around 25 mM. The concentration of the copper salt in the reagent dried on the surface of the first working electrode may be at least 75 mM, 100 mM, or 125 mM. The concentration of the copper salt in the first reagent dried on the surface of the first working electrode may be no more than 175 mM, 150 mM, or 125 mM. The concentration of the copper salt in the first reagent dried on the surface of the first working electrode may be in the range of 75-175 mM, or 100-150 mM. Preferably, the concentration of the copper salt in the first reagent dried on the surface of the first working electrode may be around 125 mM.

[0027] The concentration of the acidic buffering agent in the reagent dried on the surface of the working electrode may be at least 58 mM, 77 mM, or at least 96 mM. The concentration of the acidic buffering agent in the reagent dried on the surface of the working electrode may be no more than 134 mM, 115 mM, or no more than 96 mM. The concentration of the acidic buffering agent in the reagent dried on the surface of the working electrode may be in the range of 58-134 mM or 77-115 mM. Preferably, the concentration of the acidic buffering agent in the reagent dried on the surface of the working electrode may be around 96 mM.

[0028] For example, the concentration of copper chloride (CuCh) in the reagent dried on the surface of the working electrode may be around 25 mM and the concentration of acidic buffering agent in the reagent dried on the surface of the working electrode may be around 96 mM. Alternatively, the concentration of copper chloride (CuCh) in the reagent dried on the surface of the first working electrode may be around 100 mM and the concentration of acidic buffering agent in the first reagent dried on the surface of the first working electrode may be around 96 mM.

[0029] The term “adjacent to” includes immediately next to and abutting the working electrode, spaced apart from the working electrode and in the sample flow path upstream of the working electrode.

[0030] The copper and / or the copper salt may be provided separate to the acidic buffering agent. Providing the copper and / or the copper salt separate to the acidic buffering agent may assist in the dissolution and mixing of the reagent upon contact with a sample. The copper and / or the copper salt may be dried on the surface of the working electrode, and the acidic buffering agent may be dried adjacent to the surface of the working electrode. Alternatively, the copper and / or the copper salt may be dried adjacent to the surface of the working electrode, and the acidic buffering agent may be dried on the surface of the working electrode. Alternatively, both the copper and / or copper salt and the acidic buffering agent may be dried on the surface of the working electrode but separated from one another. Alternatively, both the copper and / or copper salt and the acidic buffering agent may be dried adjacent to the surface of the working electrode but separated from one another. In this context, dried adjacent to the surface of the working electrode may mean the reagent is dried upstream of the working electrode or next to the working electrode or on a substrate or dielectric of the sample testing device. This may allow the reagent to be provided in the flow path of the sample such that the reagent may dissolve and mix upon contact with the sample as it flows toward the working electrode.

[0031] The reagent may comprise at least one film forming agent. The reagent may comprise at least one copper chelating agent. The at least one film-forming agent and / or at least one copper chelating agent may be sodium gluconate. The at least one film forming agent and / or at least one copper chelating agent may be citrate. The at least one film-forming agent and / or at least one copper chelating agent may be ethylenediaminetetraacetic acid (EDTA). Provision of such a film forming agent and / or copper chelating agent may provide improved mechanical properties of the copper and / or copper salt and may provide faster dissolution of the copper and / or copper salt upon addition of a sample. The reagent may comrise at least one particulate, which may be a film-forming agent in some embodiments. The at least one particulate may be provided in addition to any particulate of the copper, copper salt and / or the acidic buffering agent. The at least one particulate may be homogeneously mixed with the copper salt and acidic buffering agent. The at least one particulate may be configured to retain the reagent on the surface of the working electrode and thus comprise a film- forming agent in some embodiments. The at least one particulate may be selected from the group consisting of: a montmorillonite clay, a silica-based particulate, and any combination thereof. The montmorillonite clay may be bentonite. The silica-based particulate may be cabosil M5. Provision of such particulates may form structure on the surface of the working electrode, thereby assisting in the structural immobilisation of the reagent close to the surface of the working electrode and helping to retain the reagent on the surface of the working electrode. The sample testing device may comprise a substrate. The substrate may be elongate. The substrate may be formed from an electrically insulating material. The substrate may be formed from at least one material selected from the group consisting of: polyvinyl chloride (PVC), polyethylene terephthalate (PET), polycarbonate (PC), and any combination thereof.

[0032] The or each working electrode may be provided on the substrate. The or each working electrode may be formed from at least one material selected from the group consisting of: carbon, graphite, carbon black, graphite and Prussian blue, gold, silver, and any combination thereof.

[0033] The sample testing device may comprise at least one sample chamber. The or each working electrode may be provided in a corresponding sample chamber. Each sample chamber may be separated from adjacent sample chambers.

[0034] The or each sample chamber may have a depth of at least 25 pm, more preferably of at least 50 pm, even more preferably of at least 75 pm, or most preferably of at least 100 pm. The or each sample chamber may have a depth no more than 1000 pm, more preferably no more than 500 pm, even more preferably no more than 250 pm or most preferably a depth no more than 125 pm. The or each sample chamber may have a depth in the range of 25 -1000 pm, more preferably in the range of 50-500 pm, more preferably in the range of 75-250 pm, or most preferably in the range of 100-125 pm. Preferably, the or each sample chamber may have a depth of around 100 pm. Provision of a sample chamber within the abovementioned values may assist in the efficient transfer via capillary action of at least a portion of liquid or liquidbased sample into the or each sample chamber such that the or each working electrode is covered by the liquid or liquid based sample. As such, when the or each sample chamber is full, no more liquid or liquid based sample is drawn in. This may help provide a still fluid within the or each sample chamber which may assist in providing a stable measurement.

[0035] The or each working electrode may be read using differential pulse voltammetry (DPV). DPV is a technique which minimises background charging currents, thereby offering highly sensitive readings to be determined. As such, DPV may provide more accurate readings in comparison to other commonly used techniques such as cyclic voltammetry. The or each working electrode may be read using chronoamperometry.

[0036] The sample testing device may comprise a reference electrode. The reference electrode may be provided on the substrate. The reference electrode may be configured to provide a stable reference potential. This may assist in improving the accuracy of the measurement of the potential of the or each electrode. The reference electrode may be formed from at least one material selected from the group consisting of: silver, and silver / silver chloride.

[0037] The sample collection device may comprise a counter electrode. The counter electrode may be provided on the substrate. The counter electrode may be configured to allow current from the or each working electrode to flow through the cell without increasing the current flowing through the reference electrode. The counter electrode may be formed from at least one material selected from the group consisting of carbon, graphite, gold, silver, platinum and any combination thereof.

[0038] The sample testing device may comprise at least one conductive track. The or each conductive track may be provided on the substrate. The or each conductive track may extend along the length of the substrate. The or each conductive track may be formed from an electrically conductive material. The or each conductive track may be formed from at least one material selected from the group consisting of: carbon, graphite, silver, gold and any combination thereof. The or each conductive track may be formed by at least one of screen printing, sputter coating and laser ablation.

[0039] Each of the at least one working electrode, reference electrode and counter electrode may be connected to a corresponding conductive track. Each of the at least one working electrode, reference electrode and counter electrode may be connected to a terminal end of the corresponding conductive track.

[0040] The sample testing device may be configured to receive a sample. The sample may be a liquid or liquid based sample. The liquid or liquid based sample may be at least one sample selected from the group consisting of: urine, blood, and saliva. The liquid or liquid-based sample may comprise at least one target bio-analyte. The target bio-analyte may be the protein. The target bio-analyte may be albumin.

[0041] The reagent may be a solid or particulate. Provision of a solid or particulate reagent may help retain the reagent on the working electrode prior to use. Furthermore, provision of reagents in a dry solid state also acts to enhance the stability and shelf life of the product which can be further enhanced by storing the device in a protective moisture resistant packaging.

[0042] In use, the liquid or liquid based sample may be applied directly to the reagent. The sample testing device may be configured to produce a response when the liquid or liquid-based sample is applied to the reagent. The response may indicate whether the target bio-analyte is present within the liquid or liquid-based sample. The response may indicate that the target bioanalyte is present within the liquid or liquid-based sample if the concentration of the target bioanalyte present is above a threshold value. The threshold value may be selected in accordance with the specific target bio-analyte to which the test is directed, for example a protein such as albumin. The response may indicate the concentration of target bio-analyte present within the liquid or liquid-based sample.

[0043] The sample testing device may comprise a cover. The cover may be provided over the or each working electrode, the reference electrode and the counter electrode. The cover may be formed from a hydrophilic material. The cover may be formed from at least one material selected from the group consisting of: polyvinyl chloride (PVC), polyethylene terephthalate (PET), polycarbonate (PC), and any combination thereof. The cover may comprise one or more vents.

[0044] The sample collection device may comprise an outer housing. The outer housing may surround at least a portion of the sample testing device. The outer housing may be formed from a plastics material, which may be rigid. The outer housing may comprise a gripping portion. The gripping portion may be provided distal to the at least one working electrode. The gripping portion may comprise a plurality of surface features such as ribs, or projections. As such, the user may be encouraged to grip the sample collection device away from the at least one working electrode, thereby minimising the risk of the user coming into contact with the liquid or liquidbased sample during use. The outer housing may be transparent or opaque. The outer housing may comprise at least one opening. The at least one opening may be provided over the or each working electrode. This may allow the ore each electrode to receive a sample and for the sample collection device to be read by another device such as a test reader.

[0045] According to a second aspect of the present invention there is provided a sample testing device comprising: at least a first working electrode and a second working electrode; and at least a first reagent and a second reagent; wherein the first reagent is provided on and / or adjacent to the surface of the first working electrode and the second reagent is provided on and / or adjacent to the surface of the second working electrode, wherein the first reagent comprises a protein receptor and the second reagent comprises a creatinine receptor, the creatinine receptor comprising an enzymatic receptor.

[0046] There may be provided a sample testing device comprising: at least a first working electrode and a second working electrode; and at least a first reagent and a second reagent; wherein the first reagent is provided on the surface of the first working electrode and the second reagent is provided on the surface of the second working electrode, wherein the first reagent comprises a protein receptor and the second reagent comprises a creatinine receptor, the creatinine receptor comprising an enzymatic receptor.

[0047] Provision of a device according to the second aspect of the present invention is particularly advantageous as it allows simultaneous detection of the presence of a protein and creatinine bio-analytes in a single sample. This means only a single device and single sample are required to determine the protein / creatinine ratio (P:CR), thereby helping to correct for the effects of varying sample concentration e.g., varying urine concentration, when measuring the concentration of protein present within the sample.

[0048] The enzymatic receptor may comprise creatininase, creatinase, sarcosine oxidase. The enzymatic receptor may comprise creatininase, creatinase, sarcosine oxidase, and horseradish peroxidase. Alternatively, the enzymatic receptor may comprise creatininase, creatinase, sarcosine oxidase and carbon black. Alternatively, the enzymatic receptor may comprise creatininase, creatinase, sarcosine oxidase and prussian blue.

[0049] The enzymatic receptor may comprise a 3 -enzyme cascade. The 3 -enzyme cascade may comprise creatinase, creatininase, and sarcosine oxidase. The enzymatic receptor may comprise a 4-enzyme cascade. The 4-enzyme cascade may comprise creatinase, creatininase, sarcosine oxidase, and horseradish peroxidase. Each of the enzymes in the enzymatic receptor may be co-immobilised. Each of the enzymes in the enzymatic receptor may be provided on a surface of the second working electrode. Alternatively, each of the enzymes in the enzymatic receptor may be provided adjacent to the surface of the second working electrode.

[0050] The enzymatic receptor may be dried down on and / or adjacent to the surface of the second working electrode.

[0051] The enzymatic receptor may comprise at least one buffering agent. The buffering agent may be integrated with each of the enzymes of the enzymatic receptor. Alternatively, the buffering agent may be provided separate to each of the enzymes in the enzymatic receptor. Providing the enzymes of the enzymatic receptor separate to the buffer may minimise the risk of crystallisation of the enzymes. The enzymes of the enzymatic receptor may be provided on the surface of the second working electrode, and the buffering agent may be provided adjacent to the surface of the second working electrode. Alternatively, the enzymes of the enzymatic receptor may be provided adjacent to the surface of the second working electrode, and the buffering agent may be provided on the surface of the second working electrode. Alternatively, both the enzymes of the enzymatic receptor and the buffering agent may be provided on the surface of the second working electrode but separated from one another. Alternatively, both the enzymes of the enzymatic receptor and the buffering agent may be provided adjacent to the surface of the second working electrode but separated from one another. The buffering agent may be provided as a droplet. The droplet may be dried down. In the context of the present invention, adjacent to the surface of the working electrode may mean the reagent is provided upstream of the working electrode or next to the working electrode or on a substrate or dielectric of the sample testing device. This may allow the reagent to be provided in the flow path of the sample such that the reagent may dissolve and mix upon contact with the sample as it flows toward the working electrode. The at least one buffering agent may be phosphate buffer. The enzymatic receptor may comprise at least one stabiliser. The at least one stabiliser may be selected from the group consisting of: trehalose, tween, and any combination thereof. The at least one stabiliser may be selected from the group consisting of: trehalose, glycerol, and any combination thereof. The enzymatic receptor may comprise at least one surfactant. The at least one surfactant may be Tween.

[0052] The second working electrode may be a Prussian blue electrode. The second working electrode may be a carbon black electrode. The second working electrode may be a carbon electrode. Provision of a Prussian blue and / or a carbon black electrode may facilitate direct peroxide measurement.

[0053] The second working electrode may comprise a cover. The cover may be formed from an oxygen impermeable material. The cover may be formed from a hydrophobic material. Provision of such a cover may minimise the risk of leaks. The lid and / or cover may comprise one or more vents. The one or more vents may allow oxygen from the surrounding atmosphere to drive the sarcosine oxidase reaction at the second working electrode, causing a build up of peroxide on the surface thereof. The one or more vents may be provided in a position corresponding to the second working electrode. The peroxide may be measured using at least one of the Prussian blue electrode and the carbon black electrode.

[0054] The enzymatic receptor may comprise a mediator. The mediator may be ferricyanide and / or ferrocyanide. In embodiments whereby the enzymatic receptor comprises a 3 -enzyme cascade, provision of a mediator may remove the need for providing an air vent and / or a Prussian blue or carbon black electrode. This may simplify the manufacturing process of the second working electrode. In embodiments whereby the enzymatic receptor comprises a 4- enzyme cascade, provision of a mediator may enable the peroxide product to react with the horseradish peroxidase to generate an electrochemical signal. Provision of a mediator may allow direct measurement of peroxide on a carbon electrode.

[0055] In use, the sample testing device may be configured to incubate the reaction at the second working electrode. In use, the sample testing device may be configured to incubate the reaction for a period of at least 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, or 19 minutes. In use, the sample testing device may be configured to incubate the reaction for a period no more than 20 minutes, 19 minutes, 18 minutes, 17 minutes, 16 minutes, 15 minutes, 14 minutes, 13 minutes, 12 minutes, 11 minutes, 10 minutes, 9 minutes, 8 minutes, 7 minutes, 6 minutes, 5 minutes, 4 minutes, 3 minutes, 2 minutes, or 1 minute. In use, the sample testing device may be configured to incubate the reaction at the second working electrode for a period in the range of 1-20 minutes, 2-19 minutes, 3-18 minutes, 4-17 minutes, 5-16 minutes, 6-15 minutes, 7-14 minutes, 8-13 minutes, or 9-12 minutes. In use, the sample testing device may be configured to incubate the reaction at the second working electrode for a period in the range of 1- 20 minutes, 2-18 minutes, 3-16 minutes, 4-14 minutes, 5-12 minutes. In use, the sample testing device may be configured to incubate the reaction at the second working electrode for a period in the range of 1-14 minutes, 2-13 minutes, 3-12 minutes, 4-11 minutes or 5-10 minutes. In use, the sample testing device may be configured to incubate the reaction at the second working electrode for a period in the range of 5-10 minutes. Incubating the reaction at the second working electrode may allow time for oxygen to diffuse through the air vent (where present) and for the enzyme cascade to progress in order to generate a measurable amount of end product. Furthermore, incubating the reaction at the second working electrode is particularly beneficial when testing samples of urine which have a greater concentration of creatinine (3-25 mM) as opposed to blood which has a smaller concentration of <lmM because it allows a sufficient period for the reaction to reach equilibrium so a measurement may be taken of the end product rather than during a dynamic reaction. This may extend the linear range of the measurement, thereby enabling a more accurate measurement to be taken.

[0056] The second working electrode may be configured to take chronoamperometric measurements. The second working electrode may be configured to receive an applied voltage of at least -100 mV, -150 mV, -200 mV, or -250 mV. The second working electrode may be configured to receive an applied voltage of no more than -250 mV, -200 mV, -150 mV, or -100 mV. The second working electrode may be configured to receive an applied voltage in the range of -250-0 mV, -200-0 mV, -150-0 mV, or -100-0 mV. The second working electrode may be configured to receive an applied voltage of at least 100 mV, 150 mV, 200 mV, 250 mV, 300 mV, 350 mV, or 400 mV. The second working electrode may be configured to receive an applied voltage of no more than 400 mV, 350 mV, 300 mV, 250 mV, 200 mV, 150 mV, or 100 mV. The second working electrode may be configured to receive an applied voltage in the range of 100-400 mV, 150-350 mV, 200-300 mV. The second working electrode may be configured to receive an applied voltage of 200 mV.

[0057] The protein receptor may comprise an albumin receptor. Additionally or alternatively, the protein receptor may comprise a total protein receptor. The protein receptor may detect albumin and at least one further protein. The protein receptor may detect albumin and at least two, three, four or at least five further proteins. The protein receptor may comprise a reagent which detects albumin. The protein receptor may may comprise a reagent which detects more than one protein. The reagent may detect albumin and at least one further protein, such as at least two, three, four or five further proteins. The reagent may detect total protein.

[0058] The protein receptor may comprise copper and / or a copper salt. The copper salt may be a copper (I) salt. Preferably, the copper salt may be a copper (II) salt. Preferably, the copper (II) salt may be at least one of copper sulphate (CuSCh) or copper chloride (CuCh). The copper may comprise copper particles which may in some embodiments be copper nanoparticles. The copper particles may comprise substantially pure copper, or may consist essentially of copper and trace amounts of one or more copper salts. The copper salt may be provided in the form of copper salt particles, such as copper salt nanoparticles.

[0059] The protein receptor may comprise an acidic buffering agent. The acidic buffering agent may confer a pKa of at least 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, or 5.8. The acidic buffering agent may confer a pKa no greater than 8.0, 7.9, 7.8, 7.7, 7.6, 7.5, 7.4, 7.3, 7.2, 7.1, 7.0, 6.9, 6.8, 6.7, 6.6, 6.5, 6.4, 6.3, 6.2, 6.1, 6.0, 5.9, or 5.8. The acidic buffering agent may confer a pKa in the range of 3.0-8.0, 3.1-7.9, 3.2-7.8, 3.3-7.7, 3.4-7.6, 3.5-7.5, 3.6-7.4, 3J7-7.3, 3.8-7.2, 3.9-7.1, 4.0-7.0, 4.1-6.9, 4.2-6.8, 4.3-6.7, 4.4-6.6, 4.5-6.5, 4.6-6.4, 4.7-6.3, 4.8-6.2, 4.9-6.1, 5.0-6.0, 5.1- 5.9, 5.2-5.8, 5.3-5.7, or 5.4-5.6. The acidic buffering agent may confer a pKa in the range of 3.0-8.0, 3.0-7.5, 3.0-7.0, 3.0-6.5, 3.0-6.0, or 3.0-5.5. The acidic buffering agent may confer a pKa in the range of 3.5- 8.0, 3.5-7.5, 3.5-7.0, 3.5-6.5, 3.5-6.0, 3.5-5.5, or 3.5-5.0. The acidic buffering agent may confer a pKa in the range of 4.0-8.0, 4.0-7.5, 4.0-7.0, 4.0-6.5, 4.0-6.0, 4.0-5.5, or 4.0-5.0. The acidic buffering agent may confer a pKa in the range of 4.5-8.0, 4.5-7.5, 4.5-7.0, 4.5-6.5, 4.5-6.0, 4.5- 5.5, or 4.5-5.0. The acidic buffering agent may confer a pKa in the range of 5.0-8.0, 5.0-7.5, 5.0-7.0, 5.0-6.5, 5.0-6.0, or 5.0-5.5. Preferably, the acidic buffering agent may confer a pKa in the range of 3.0-8.0. This may assist in maintaining the optimal pH range for the reaction between the protein, the bio-analyte in the sample and the protein receptor. In particular, provision of the acidic buffering agent may help maintain a stable pH range, thereby improving the accuracy of measurements recorded using the or each electrode. This is particularly advantageous when the sample testing device is used to test urine whose pH may range from pH 4-8.

[0060] The acidic buffering agent may be at least one agent selected from the group consisting of: acidified phosphate buffer, MES buffer, sodium acetate, and any combination thereof. The acidic buffering agent may be at least one agent selected from the group consisting of: acidified phosphate buffer, MES buffer, sodium acetate, L-tartaric acid, maleic acid and any combination thereof.

[0061] The ratio of copper salt to acidic buffering agent in the first reagent may be 4:1. For example, the ratio of the copper salt copper chloride (CuCh) to acidic buffering agent in the first reagent may be 4: 1. Alternatively, the ratio of copper salt to acidic buffering agent in the first reagent may be 1:1. For example, the ratio of the copper salt copper chloride (CuCh) to acidic buffering agent in the first reagent may be 1:1.

[0062] The concentration of copper salt in the first reagent before it is dried on the surface of the working electrode may be at least 130 mM, 140 mM, or 150 mM. The concentration of copper salt in the first reagent before it is dried on the surface of the first working electrode may be no more than 170 mM, 160 mM, or 150 mM. The concentration of copper salt in the first reagent before it is dried on the surface of the first working electrode may be in the range of 130-170 mM, or 140-160 mM. Preferably the concentration of copper salt in the first reagent before it is dried on the surface of the first working electrode may be around 150 mM. The concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be at least 120 mM, 130 mM, 140 mM, 150 mM, 160 mM, 170 mM, 180 mM, 190 mM, 200 mM, 210 mM, 220 mM, 230 mM, 240 mM, 250 mM, 260 mM, 270 mM, 280 mM, 290 mM, 300 mM, 310 mM, 320 mM, 330 mM, 340 mM, 350 mM, 360 mM, 370 mM, 380 mM, 390 mM, 400 mM, 410 mM, 420 mM, 430 mM, 440 mM, 450 mM, 460 mM, 470 mM, 480 mM, 490 mM, 500 mM, 510 mM, 520 mM, 530 mM, 540 mM, 550 mM, 560 mM, 570 mM, 580 mM, 590 mM, 600 mM, 610 mM, 620 mM, 630 mM, 640 mM, 650 mM, 660 mM, 670 mM, 680, mM690 mM, 700 mM, 710 mM, 720 mM, 730 mM, 740 mM, 750 mM, 760 mM, 770 mM, 780 mM, 790 mM, 800 mM, 810 mM, 820 mM, 830 mM, 840 mM, 850 mM, 860 mM, 870 mM, 880 mM, 890 mM, 900 mM, 910 mM, 920 mM, 930 mM, 940 mM, 950 mM, or 960 mM. The concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be no more than 960 mM, 950 mM, 940 mM, 930 mM, 920 mM, 910 mM, 900 mM, 890 mM, 870 mM, 860 mM, 850 mM, 840 mM, 830 mM, 820 mM, 810 mM, 800 mM, 790 mM, 780 mM, 770 mM, 760 mM, 750 mM, 740 mM, 730 mM, 720 mM, 710 mM, 700 mM, 690 mM, 680 mM, 670 mM, 660 mM, 650 mM, 640 mM, 630 mM, 620 mM, 610 mM, 600 mM, 590 mM, 580 mM, 570 mM, 560 mM, 550 mM, 540 mM, 530 mM, 520 mM, 510 mM, 500 mM, 490 mM, 480 mM, 470 mM, 460 mM, 450 mM, 440 mM, 430 mM, 420 mM, 410 mM, 400 mM, 390 mM, 380 mM, 370 mM, 360 mM, 350 mM, 340 mM, 330 mM, 320 mM, 310 mM, 300 mM, 290 mM, 280 mM, 270 mM, 260 mM, 250 mM, 240 mM, 230 mM, 220 mM, 210 mM, 200 mM, 190 mM, 180 mM, 170 mM, 160 mM, 150 mM, 140 mM, 130 mM, 120 mM. The concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be in the range of 120 - 960 mM, 220- 940 mM, 320-920 mM, 420-900 mM, 520-880 mM, 620-860 mM, or 720-840 mM. Preferably the concentration of copper salt in the reagent before it is dried on the surface of the working electrode may be around 720 mM.

[0063] The concentration of acidic buffering agent in the first reagent before is it dried on the surface of the first working electrode may be at least 520 mM, 560 mM, 600 mM. The concentration of acidic buffering agent in the first reagent before is it dried on the surface of the working electrode may be no more than 680 mM, 640 mM, 600 mM. The concentration of acidic buffering agent in the first reagent before is it dried on the surface of the first working electrode may be in the range of 520-680 mM or 560-640 mM. Preferably the concentration of acidic buffering agent in the first reagent before it is dried on the surface of the first working electrode is around 600 mM. The concentration of acidic buffering agent in the reagent before it is dried on the surface of the working electrode may be at least 520 mM, 540 mM, 560 mM, 580 mM, 600 mM, 620 mM, 640 mM, 660 mM, 680 mM, 700 mM, 720 mM, 740 mM, 760 mM, 780 mM, 800 mM, 820 mM, 840 mM, 860 mM, 880 mM, 900 mM, 920 mM, 940 mM, 960 mM, 980 mM, 1000 mM. The concentration of acidic buffering agent in the reagent before is it dried on the surface of the working electrode may be no more than 1000 mM, 980 mM, 960 mM, 940 mM, 920 mM, 800 mM, 780 mM, 760 mM, 740 mM, 720 mM, 700 mM, 680 mM, 660 mM, 640 mM, 620 mM, 600 mM, 580 mM, 560 mM, 540 mM, 520 mM. The concentration of acidic buffering agent in the reagent before is it dried on the surface of the working electrode may be in the range of 520-1000 mM, 620 mM-850 mM, 720-800 mM. Preferably the concentration of acidic buffering agent in the reagent before it is dried on the surface of the working electrode is around 750 mM.

[0064] For example, the concentration of copper chloride (CuCh) in the first reagent before it is dried on the surface of the first working electrode may be around 150 mM and the concentration of acidic buffering agent in the first reagent before it is dried on the surface of the first working electrode may be around 600 mM.

[0065] The concentration of the copper salt in the reagent dried on the surface of the first working electrode may be at least 15 mM, 20 mM, or 25 mM. The concentration of the copper salt in the first reagent dried on the surface of the first working electrode may be no more than 35 mM, 30 mM, or 25 mM. The concentration of the copper salt in the first reagent dried on the surface of the first working electrode may be in the range of 15-35 mM or 20-30 mM. Preferably, the concentration of the copper salt in the first reagent dried on the surface of the first working electrode may be around 25 mM. The concentration of the copper salt in the reagent dried on the surface of the first working electrode may be at least 75 mM, 100 mM, or 125 mM. The concentration of the copper salt in the first reagent dried on the surface of the first working electrode may be no more than 175 mM, 150 mM, or 125 mM. The concentration of the copper salt in the first reagent dried on the surface of the first working electrode may be in the range of 75-175 mM, or 100-150 mM. Preferably, the concentration of the copper salt in the first reagent dried on the surface of the first working electrode may be around 125 mM.

[0066] The concentration of the acidic buffering agent in the first reagent dried on the surface of the first working electrode may be at least 58 mM, 77 mM, or 96 mM. The concentration of the acidic buffering agent in the first reagent dried on the surface of the first working electrode may be no more than 134 mM, 115 mM, or 96 mM. The concentration of the acidic buffering agent in the first reagent dried on the surface of the first working electrode may be in the range of 58-134 mM or 77-115 mM. Preferably, the concentration of the acidic buffering agent in the first reagent dried on the surface of the first working electrode may be around 96 mM.

[0067] For example, the concentration of copper chloride (CuCh) in the reagent dried on the surface of the first working electrode may be around 25 mM and the concentration of acidic buffering agent in the first reagent dried on the surface of the first working electrode may be around 96 mM. Alternatively, the concentration of copper chloride (CuCh) in the reagent dried on the surface of the first working electrode may be around 100 mM and the concentration of acidic buffering agent in the first reagent dried on the surface of the first working electrode may be around 96 mM.

[0068] The copper and / or the copper salt may be provided separate to the acidic buffering agent. Providing the copper and / or the copper salt separate to the acidic buffering agent may assist in the dissolution and mixing of the reagent upon contact with a sample. The copper and / or the copper salt may be dried on the surface of the working electrode, and the acidic buffering agent may be dried adjacent to the surface of the working electrode. Alternatively, the copper and / or the copper salt may be dried adjacent to the surface of the working electrode, and the acidic buffering agent may be dried on the surface of the working electrode. Alternatively, both the copper and / or copper salt and the acidic buffering agent may be dried on the surface of the working electrode but separated from one another. Alternatively, both the copper and / or copper salt and the acidic buffering agent may be dried adjacent to the surface of the working electrode but separated from one another.

[0069] The protein receptor may comprise at least one film forming agent. The protein receptor may comprise at least one copper chelating agent. The at least one film-forming agent and / or at least one copper chelating agent may be sodium gluconate. The at least one film forming agent and / or at least one copper chelating agent may be citrate. The at least one film-forming agent and / or at least one copper chelating agent may be ethylenediaminetetraacetic acid (EDTA). Provision of such a film forming agent and / or copper chelating agent may provide improved mechanical properties of the copper and / or copper salt and may provide faster dissolution of the copper and / or copper salt upon addition of a sample.

[0070] The first working electrode may be read using differential pulse voltammetry (DPV). DPV is a technique which minimises background charging currents, thereby offering highly sensitive readings to be determined. As such, DPV may provide more accurate readings in comparison to other commonly used techniques such as cyclic voltammetry. The first working electrode may be read using chronoamperometry.

[0071] The second working electrode may be configured to take amperometric measurements. The second working electrode may be configured to take chronoamperometric measurements.

[0072] The sample testing device may comprise a third working electrode. The third working electrode may be an ion selective electrode. The third working electrode may be configured to take potentiometric measurements. The sample testing device may comprise a third reagent. The third reagent may be provided on the surface of the third working electrode. The third reagent may comprise a potassium receptor. The potassium receptor may comprise valinomycin. The potassium receptor may comprise 2-Dodecyl-2-methyl- 1,3 -propanediyl bis[N-[5'-nitro(benzo-15-crown-5)-4'-yl]carbamate]. The potassium receptor may comprise a counter ion. The counter ion may be potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. The potassium receptor may comprise a membrane. The membrane may be formed from polyvinyl chloride (PVC). The potassium receptor may comprise at least one plasticiser. The at least one plasticiser may be selected from the group consisting of: dioctyl sebacate (DOS), 2-nitrophenyl octyl ether (NPOE), and any combination thereof.

[0073] The sample testing device may comprise a fourth working electrode. The fourth working electrode may be an ion selective electrode. The fourth working electrode may be configured to take potentiometric measurements. The sample testing device may comprise a fourth reagent. The fourth reagent may be provided on the surface of the fourth working electrode. The fourth reagent may comprise a sodium receptor. The sodium receptor may comprise a sodium ionophore. The sodium ionophore may comprise sodium ionophore VI (Bis[(12-crown-4)methyl] dodecylmethylmalonate). The sodium receptor may comprise a counter ion. The counter ion may comprise sodium tetrakis [3,5- bis(trifluoromethyl)phenyl]borate). The sodium reagent may comprise a membrane. The membrane may be formed from polyvinyl chloride (PVC). The sodium receptor may comprise at least one plasticiser. The at least one plasticiser may be selected from the group consisting of: dioctyl sebacate (DOS), 2-nitrophenyl octyl ether (NPOE), and any combination thereof.

[0074] Provision of the sample testing device of the second aspect of the claimed invention which is further capable of testing for potassium and sodium is particularly advantageous as both tests provide an indication of a user’ s cardiovascular health. As protein / creatinine ratio (P:CR) is widely acknowledged to be an indicator of several health outcomes including kidney health, chronic kidney disease, and cardiovascular health, this device may provide a more detailed overview of the patient’s health.

[0075] The sample testing device may comprise a fifth working electrode. The fifth working electrode may be an ion selective electrode. The fifth working electrode may be configured to take potentiometric measurements. The sample testing device may comprise a fifth reagent. The fifth reagent may be provided on the surface of the fifth working electrode. The fifth reagent may comprise a pH detector reagent. The pH detector reagent may comprise a hydrogen ionophore. The hydrogen ionophore may comprise hydrogen ionophore II (4- Nonadecylpyridine). The pH detector reagent may comprise a counter ion. The counter ion may comprise sodium tetrakis [3,5-bis(trifluoromethyl)phenyl]borate). The pH detector reagent may comprise a membrane. The membrane may be formed from polyvinyl chloride (PVC). The pH detector reagent may comprise at least one plasticiser. The at least one plasticiser may be selected from the group consisting of: dioctyl sebacate (DOS), 2-nitrophenyl octyl ether (NPOE), and any combination thereof.

[0076] The sample testing device may comprise a sixth working electrode. The sixth working electrode may be configured to take amperometric measurements. The sample testing device may comprise a sixth reagent. The sixth reagent may be provided on the surface of the sixth working electrode. The sixth reagent may be provided on and / or adjacent to the surface of the sixth working electrode. The sixth reagent may comprise a haemoglobin receptor. The haemoglobin receptor may comprise the solid oxidant lithium perchlorate and carbon black. Alternatively, the haemoglobin receptor may comprise a mediator and a hydrogen peroxide generating enzyme. The mediator may comprise an osmium compound. The hydrogen peroxide generating enzyme may comprise glucose oxidase and its substrate. The haemoglobin receptor may comprise at least one buffering agent. The at least one buffering agent may comprise a phosphate buffer. The haemoglobin receptor may comprise at least one lysing agent. The at least one lysing agent may be saponin. Provision of a lysing agent may enable lysing of red blood cells, thereby enabling the haemoglobin receptor to detect haemoglobin within the red blood cells. The haemoglobin receptor may be configured to detect haemoglobinuria.

[0077] The sample testing device may comprise a seventh working electrode. The seventh working electrode may be configured to take amperometric measurements The sample testing device may comprise a seventh reagent. The seventh reagent may be provided on the surface of the seventh working electrode. The seventh reagent may be provided on and / or adjacent to the surface of the seventh working electrode. The seventh reagent may comprise a glucose receptor. The glucose receptor may comprise glucose oxidase. The glucose receptor may comprise glucose dehydrogenase. The glucose receptor may comprise at least one buffering agent. The buffering agent may comprise a phosphate buffer. Provision of a buffering agent such as a phosphate buffer may assist in ensuring reliable performance of the sample testing device in various pH conditions, for example caused by variations in concentration of the liquid or liquid-based sample. The glucose receptor may comprise at least one stabiliser. The stabiliser may comprise trehalose. The glucose receptor may comprise at least one mediator. The mediator may be selected from the group consisting of: ruthenium hexamine, ferricyanide, ferrocene, and any combination thereof. The mediator may be selected from the group consisting of: ruthenium hexamine, ferricyanide, ferrocene, methylene blue, and any combination thereof. Provision of a mediator may assist in the rapid transfer of electrons, resulting in an efficient test. The glucose receptor may comprise at least one surfactant. The surfactant may comprise tween 20. Provision of a surfactant may ensure effective coverage of the electrode. Provision of such a glucose receptor enables the device to provide a broader overview of the user’s health and in particular, to provide an indication of whether the user may be pre-diabetic or diabetic.

[0078] The sample testing device may comprise an eighth working electrode. The eighth working electrode may be configured to take amperometric measurements or chronoamperometric measurements. The eighth working electrode may comprise an eighth reagent. The eighth reagent may be provided on the surface of the eighth working electrode. The eighth reagent may be provided on and / or adjacent to the surface of the eighth working electrode. The eighth reagent may comprise a creatine receptor. Provision of a creatine receptor may allow for correction of the creatinine measurement taken at the second working electrode. The creatine receptor may comprise an enzymatic receptor. The creatine receptor may comprise creatinase, sarcosine oxidase. The creatine receptor may comprise creatinase, sarcosine oxidase, and horseradish peroxidase. Each of the enzymes in the creatine receptor may be coimmobilised. Each of the enzymes in the creatine receptor may be provided on a surface of the second working electrode. Alternatively, each of the enzymes in the creatine receptor may be provided adjacent to the surface of the eighth working electrode. The creatine receptor may comprise at least one buffering agent. The at least one buffering agent may be phosphate buffer. The creatine receptor may comprise at least one stabiliser. The at least one stabiliser may be selected from the group consisting of: trehalose, glycerine, tween, and any combination thereof. The enzymatic receptor may comprise at least one surfactant. The at least one surfactant may be Tween. The creatine receptor may comprise at least one mediator. The at least one mediator may be ferricyanide and / or ferrocyanide. The eighth working electrode may be a Prussian blue electrode. The eighth working electrode may be a carbon black electrode. The eighth working electrode may be a carbon electrode.

[0079] The sample testing device may comprise a substrate. The substrate may be elongate. The substrate may be formed from an electrically insulating material. The substrate may be formed from at least one material selected from the group consisting of: polyvinyl chloride (PVC), polyethylene terephthalate (PET), polycarbonate (PC) and any combination thereof. . . .

[0080] The or each working electrode may be provided on the substrate. The or each working electrode may be formed from at least one material selected from the group consisting of: carbon, graphite, carbon black, graphite and Prussian blue, gold, silver, and any combination thereof.

[0081] At least one reagent may be dried on the surface of the corresponding working electrode. Each reagent may be dried on the surface of their corresponding working electrode. Preferably, at least the first reagent may be dried on the surface of the first working electrode. Providing a reagent dried on the surface of the working electrode means no additional materials are required for the integration of the reagent such as a membrane, fabric, or filter. This may help reduce the complexity and therefore the cost of the device.

[0082] The or each reagent may comprise at least one particulate. The or each particulate may comprise a film-forming agent. The at least one particulate may be provided in addition to any particulate receptor component of the or each reagent. The at least one particulate may be homogeneously mixed with the or each particulate receptor component of the or each reagent. Preferably, at least the first reagent may comprise at least one particulate. The at least one particulate may be provided in addition to any particulate of the copper, copper salt and / or the acidic buffering agent of the first reagent. The at least one particulate may be homogeneously mixed with the copper and / or copper salt and acidic buffering agent of the first reagent. The at least one particulate may be configured to retain the reagent on the surface of the corresponding working electrode and thus may comprise a film- forming agent in some embodiments. The at least one particulate may be selected from the group consisting of: a montmorillonite clay, a silica-based particulate, and any combination thereof. The montmorillonite clay may be bentonite. The silica-based particulate may be cabosil M5. Provision of such particulates may form structure on the surface of the working electrode, thereby assisting in the structural immobilisation of the reagent close to the surface of the corresponding working electrode and helping to retain the reagent on the surface of the working electrode. Each working electrode may be provided on the substrate.

[0083] The or each working electrode configured to take amperometric measurements may be grouped together in a series. The or each working electrode configured to take potentiometric measurements may be grouped together in a series. The or each working electrode configured to take chronoamperometric measurements may be grouped together in a series. This may help the electrodes to be easily read as when the sample testing device is read, for example by a test reader, the amperometric working electrodes may form part of a separate circuit to the potentiometric working electrodes.

[0084] In a configuration in which one or more working electrodes for potentiometric measurements are provided on the sample testing device with one or more working electrodes for amperometric measurements, the one or more working electrodes for potentiometric measurements and one or more working electrodes for amperometric measurements are preferably provided on separate portions of the sample testing device. This separation may minimise noise (e.g. from leakage currents) between the one or more working electrodes for potentiometric measurements and one or more working electrodes for amperometric measurements.

[0085] The sample testing device may comprise a reference electrode. The reference electrode may be provided on the substrate. The reference electrode may be configured to provide a stable reference potential. This may assist in improving the accuracy of the measurement of the potential of the or each working electrode. The reference electrode may be formed from at least one material selected from the group consisting of: silver and silver / silver chloride.

[0086] The sample testing device may comprise a counter electrode. The counter electrode may be provided on the substrate. The counter electrode may be configured to allow current from the or each working electrode to flow through the cell without increasing the current through the reference electrode. The counter electrode may be formed from at least one material selected from the group consisting of carbon, graphite, gold, silver, platinum and any combination thereof.

[0087] The sample testing device may comprise at least one conductive track. The or each conductive track may be provided on the substrate. The or each conductive track may extend along the length of the substrate. The or each conductive track may be formed from an electrically conductive material. The or each conductive track may be formed from at least one material selected from the group consisting of: carbon, graphite, silver, silver / silver chloride, gold and any combination thereof. The or each conductive track may be formed by at least one of screen printing, sputter coating or laser ablation.

[0088] Each working electrode, the reference electrode and the counter electrode may be connected to a corresponding conductive track. Each working electrode, the reference electrode and the counter electrode may be connected to a terminal end of the corresponding conductive track.

[0089] The sample testing device may comprise at least two sample chambers. Each working electrode may be housed in a corresponding sample chamber. The sample testing device may comprise a flow channel. The flow channel may extend longitudinally. Each sample chamber may extend from the flow channel. Each sample chamber may extend laterally from the flow channel.

[0090] The or each sample chamber may have a defined volume. Sample chambers having a defined volume may help limit diffusion of each reagent away from the corresponding working electrode during use. Furthermore, a high buffer concentration (where buffering agent is present) may be maintained in the immediate vicinity of the corresponding working electrode thereby increasing its buffering capacity. This solution is preferable to adding an excess of acidic buffering agent, which may have other effects on the product performance such as slower dissolution of the reagent.

[0091] The sample testing device may be configured to receive a sample. The sample may be a liquid or liquid based sample. The liquid or liquid based sample may be at least one sample selected from the group consisting of: urine, blood, and saliva. The liquid or liquid-based sample may comprise at least one target bio-analyte. The target bio-analyte may be at least one bio-analyte selected from the group consisting of: a protein, albumin, creatinine, sodium, potassium, pH, haemoglobin, glucose, and any combination thereof. The target bio-analyte may be creatine. Each working electrode may be housed at an end of the sample chamber distal to the flow channel. Each sample chamber may be arranged in a series. As such, when the liquid or liquid-based sample enters the sample testing device, the sample may flow into each sample chamber in turn. Each sample chamber may be delimited by at least one wall. The at least one wall may block the flow of liquid or liquid-based sample between each sample chamber.

[0092] At least one reagent may be a solid or particulate. Provision of a solid or particulate reagent may help retain the reagent on the electrode prior to use. Furthermore, provision of reagents in a dry solid state also acts to enhance the stability and shelf life of the product which can be further enhanced by storing the device in a protective moisture resistant packaging.

[0093] In use, the liquid or liquid based sample may be applied directly to at least one reagent. Alternatively, the liquid or liquid-based sample may be released into the flow channel. The liquid or liquid-based sample may be released into the flow channel via an opening in the flow channel proximal to an edge of the substrate.

[0094] Each sample chamber may have a depth of at least 25 pm, more preferably of at least 50 pm, even more preferably of at least 75 pm, or most preferably of at least 100 pm. Each sample chamber may have a depth no more than 1000 pm, more preferably no more than 500 pm, even more preferably no more than 250 pm or most preferably a depth no more than 125 pm. Each sample chamber may have a depth in the range of 25 -1000 pm, more preferably in the range of 50-500 pm, more preferably in the range of 75-250 pm, or most preferably in the range of 100-125 pm. Preferably, each sample chamber may have a depth of around 100 pm. Provision of a sample chamber within the abovementioned values may assist in the efficient transfer via capillary action of at least a portion of released liquid or liquid-based sample from the flow channel into the or each sample chamber via the flow channel such that the or each working electrode is covered by the liquid or liquid based sample. As such, when the or each sample chamber is full, no more liquid or liquid based sample is drawn in. This may help provide a still fluid within each sample chamber which may assist in providing a stable measurement.

[0095] The sample testing device may comprise a sample storage portion. The sample storage portion may be in liquid communication with each sample chamber. The sample storage portion may be in liquid communication with each sample chamber via the flow channel. The sample storage portion may be in liquid communication with each sample chamber via the opening in the flow channel proximal to the edge of the substrate. The sample storage portion may be configured to at least temporarily store the liquid or liquid based sample as a stored liquid or liquid-based sample. The sample storage portion may be actuable to release at least a portion of the stored liquid or liquid-based sample. Preferably, the sample storage portion may be actuable to release a fixed volume of the stored liquid or liquid-based sample. This may enable a fixed volume of liquid or liquid-based sample to be released following a non-metered collection i.e., whereby an unknown volume of sample has been collected, such as during urine collection, thereby enabling a quantitative result to be produced from a test in which a fixed volume of sample is required.

[0096] A barrier or valve or similar may be provided between the sample storage portion and the flow channel. The barrier or valve or similar may be moveable from a first position to a second position. In the first position, the barrier or valve or similar may block liquid communication between the sample storage portion and the flow channel. In the second position, the barrier or valve or similar may allow liquid communication between the sample storage portion and the flow channel. The barrier or valve or similar may be at least one of a seal or a pierceable material or film. Provision of such a barrier or valve or similar may assist in retaining the liquid or liquid-based sample within the sample storage portion until a suitable time for the sample to be tested.

[0097] Each working electrode may be configured to produce a response when the liquid or liquid-based sample contacts the corresponding reagent. Each response may indicate whether the specific target bio-analyte to which the corresponding reagent is directed is present within the liquid or liquid-based sample. Each response may indicate that the target bio-analyte to which the corresponding reagent is directed is present within the liquid or liquid-based sample if the concentration of the target bio-analyte present is above a threshold value. The threshold value may be selected in accordance with the specific target bio-analyte to which the corresponding reagent is directed, for example a protein such as albumin or creatinine. The response may indicate the concentration of target bio- analyte present within the liquid or liquidbased sample.

[0098] The sample testing device may comprise a cover. The cover may be provided over the or each working electrode, the reference electrode and the counter electrode. The cover may be formed from a hydrophilic material. The cover may be formed from at least one material selected from the group consisting of: polyvinyl chloride (PVC), polyethylene terephthalate (PET), polycarbonate (PC) and any combination thereof. The cover may comprise one or more vents.

[0099] The sample collection device may comprise an outer housing. The outer housing may surround at least a portion of the sample testing device. The outer housing may be formed from a plastics material, preferably a rigid plastics material. The outer housing may comprise a gripping portion. The gripping portion may be provided distal to each working electrode. The gripping portion may comprise a plurality of surface features such as ribs, or projections. As such, the user may be encouraged to grip the sample testing device away from each working electrode, thereby minimising the risk of the user coming into contact with the liquid or liquidbased sample during use. The outer housing may be transparent or opaque. The outer housing may comprise at least one opening. The at least one opening may be provided over each working electrode. This may allow the or each working electrode to receive a sample and for the sample collection device to be read by another device such as a test reader.

[0100] According to a third aspect of the present invention there is provided a test reader configured to read the sample testing device of any aspect of the present invention, the test reader comprising a sensing portion having at least one sensor configured to read at least one working electrode of the sample testing device.

[0101] The number of sensors may be selected in accordance with the number of working electrodes of the sample testing device.

[0102] The test reader may use differential pulse voltammetry (DPV) to read the or each working electrode of the sample testing device. DPV is a technique which minimises background charging currents, thereby offering highly sensitive readings to be determined. As such, DPV may provide more accurate readings in comparison to other commonly used techniques such as cyclic voltammetry.

[0103] The test reader may use chronoamperometry to read the or each working electrode of the sample testing device. The test reader may use potentiometry to read the or each working electrode of the sample testing device.

[0104] The test reader may be configured to read the or each working electrode and indicate whether the or each target bio-analyte is present within a sample in the sample collection device. The test reader may indicate whether the or each target bio-analyte is present within the sample if the concentration of the target bio-analyte present is above a threshold value. Alternatively, the test reader may indicate whether the or each target bio-analyte is present within the sample if the concentration of the or each target detected is above a threshold value. The test reader may indicate the concentration of the or each target bio-analyte present within the sample. The test reader may be configured to output a reading. The test reader may be configured to output a calibrated reading. For example, the test reader may be configured to output each reading relative to a creatinine reading.

[0105] The test reader may store at least one reference curve or reference database. Preferably, the test reader may comprise at least one reference curve or reference database corresponding to the or each working electrode and its corresponding reagent. The test reader may be configured to compare the or each reading from the or each working electrode with the corresponding reference curve or reference database to determine the concentration of the target bio-analyte present within the sample. The or each reference curve or reference database may indicate the relationship between the current or voltage read and the concentration of the target bio-analyte present within the sample.

[0106] The test reader may comprise a user interface. The user interface may comprise a touchscreen. The reading may be output via the touchscreen. Alternatively, the test reader may comprise a first data link. The first data link may be provided between the test reader and a cloud service platform. The reading may be output to the cloud service platform. As such, the results may be received by an external user such as a doctor, medical worker, or data analyst. Additionally or alternatively, the test reader may comprise a second data link. The second data link may be provided between the test reader and an electronic device. The second data link may comprise the first data link, i.e., the second data link may be provided via the cloud service platform. The electronic device may be a mobile phone, tablet, or computer for example. As such, the test reader may enable the user to receive the readings via their personal electronic device, for example in an app which may be used to track a user’s health metrics.

[0107] The test reader may be configured to receive the sample collection device. The test reader may comprise an opening. The opening may correspond in size and / or shape to the sample testing device. The test reader may be configured to actuate the sample storage portion (where present) of the sample testing device upon insertion of the sample collection device to release at least a portion of the stored liquid sample into the flow channel and / or the or each sample chamber.

[0108] The test reader may preferably comprise a reader portion corresponding to the or each working electrode of the sample testing device.

[0109] The test reader may be configured to read the or each working electrode after a predetermined period of time. The test reader may be configured to read each working electrode after a different predetermined period of time. As such, the reader may automatically read each working electrode after the correct period of time, helping to minimise errors in measurement.

[0110] According to a fourth aspect of the present invention there is provided a system for testing a liquid or liquid-based sample, the system comprising: a. the sample testing device of the first or second aspect; and b. the test reader of the third aspect.

[0111] The sample testing device may optionally comprise any optional features of the first or second aspects of the present invention. The test reader may optionally comprise any optional features of the third aspect of the present invention.

[0112] According to a fifth aspect of the present invention there is provided a method of testing a sample using a sample testing device comprising the steps of: a. providing a sample testing device according to the first or second aspects; b. providing the sample testing device with a liquid sample; and c. testing the sample using the sample testing device to detect specific targets within the sample.

[0113] The method may comprise using a test reader of the third aspect of the invention to read the results of the test. The sample testing device may be part of a system of the fourth aspect of the invention.

[0114] Detailed Description of the Invention

[0115] In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

[0116] Figure 1 shows an exploded view of the sample testing device of the present invention;

[0117] Figure 2 shows a differential pulse voltammogram of the first receptor of the device of the present invention reacting with the target bio-analyte albumin;

[0118] Figure 3 shows a plot of mean current versus albumin concentration;

[0119] Figure 4 shows a logarithmic plot of mean potential versus potassium concentration;

[0120] Figure 5 shows a logarithmic plot of mean potential versus sodium concentration;

[0121] Figure 6 shows a linear plot of mean potential versus pH; Figure 7 shows a plot of mean current versus creatinine concentration;

[0122] Figure 8 shows a plot of mean current versus haemoglobin concentration;

[0123] Figure 9 shows a plot of mean current versus glucose concentration;

[0124] Figure 10 shows a plot of mean potential versus potassium concentration;

[0125] Figure 11 shows a plot of mean potential versus pH;

[0126] Figure 12 shows a plot of mean current versus creatinine concentration wherein the measurement is taken using chronoamperometry;

[0127] Figure 13 shows a plot of mean current versus creatinine concentration wherein the measurement is taken using chronoamperometry;

[0128] Figure 14 shows a plot of mean current versus creatinine concentration wherein the measurement is taken using chronoamperometry;

[0129] Figure 15 shows a logarithmic plot of mean current versus haemoglobin concentration;

[0130] Figure 16 shows a mean current versus glucose concentration;

[0131] Figure 17 shows a logarithmic plot of mean potential versus sodium concentration;

[0132] Figure 18 shows a plot of mean current versus total protein concentration wherein the measurement is taken using chronoamperometry; and

[0133] Figure 19 shows a plot of mean current versus total protein concentration wherein the measurement is taken using differential pulse voltammetry.

[0134] With reference initially to Figure 1, a sample testing device 1 is shown. The sample testing device 1 comprises an elongate rectangular substrate 2 formed from an electrically insulating material. In this particular embodiment, there are seven working electrodes 3 provided on the substrate 2 although the person skilled in the art will understand that a greater or lesser number of working electrodes 3 may also be provided.

[0135] Each working electrode 3 comprises a corresponding reagent 4 dried on the surface of the working electrode 3. Nevertheless, the skilled person will appreciate that in alternative embodiments, the reagent may be dried on and / or adjacent to the surface of the working electrode. Provision of a solid reagent 4 helps to retain the reagent on the surface of the working electrode 3 prior to use and enhances the stability and shelf life of the sample testing device. A first reagent 4a is provided on the surface of the first working electrode 3 a. The first reagent 4a comprises a protein receptor in the form of an albumin receptor. The albumin receptor may detect albumin and at least one other protein. Alternatively, the skilled person will appreciate that the protein receptor may comprise a total protein receptor. In this embodiment, the albumin receptor comprises a copper (II) salt in the form of either copper sulphate (CuSCh) or copper chloride (CuCh). In other examples the protein receptor may comprise elemental copper, such as in the form of copper nanoparticles (which may provide an albumin receptor). The first reagent 4a further comprises an acidic buffering agent which confers a pKa of between 3.0 and 8.0 and may be selected from the group of acidic buffering agents consisting of: acidified phosphate buffer, MES buffer, sodium acetate, L-tartaric acid, maleic acid, and any combination thereof. The first reagent 4a also comprises at least one particulate provided in addition to and mixed homogeneously with any particulate of copper salt and acidic buffering agent. The at least one particulate is configured to retain the first reagent 4a on the surface of the first working electrode 3 a and is selected from the group consisting of: a montmorillonite clay, a silica-based particulate, and any combination thereof.

[0136] The first working electrode 3 a is configured to produce a response when a liquid or liquid based sample comprising the bio-analyte albumin contacts the first reagent 4a and is configured to be read using differential pulse voltammetry (DPV). In alternative embodiments, the skilled person will appreciate that the first working electrode 3 a may also be configured to be read using chronoamperometry. Provision of the acidic buffering agent assists in maintaining the optimal pH range for the reaction between albumin, the bio-analyte in the sample and the albumin receptor, thereby helping to improve the accuracy of measurements recorded using the first electrode 3a. This is particularly advantageous when the sample testing device 1 is used to test urine whose pH may range from pH 4-8.

[0137] A second reagent 4b is provided on the surface of the second working electrode 3b. The second reagent 4b comprises a creatinine receptor which is an enzymatic receptor. In this particular embodiment, the enzymatic receptor comprises creatininase, creatinase, sarcosine oxidase, and horseradish peroxidase however, the skilled person will appreciate that alternative enzymatic receptors may also be used.

[0138] The second working electrode 3b is configured to take amperometric measurements and to produce a response when a liquid or liquid based sample comprising the bio-analyte creatinine contacts the second reagent 4b. The skilled person will appreciate that in alternative embodiments, the second working electrode may be configured to take chronoamperometric measurements. By measuring the concentration of creatinine present within a liquid or liquid based sample, measurements of different bio-analytes such as the protein albumin may be provided as an albumin / creatinine ratio. This may improve the accuracy of the measurement of albumin concentration in a urine sample for example as the concentration of creatinine corrects for the concentration of the urine when the sample is taken.

[0139] A third reagent 4c is provided on the surface of the third working electrode 3c. The third regent 4c comprises a potassium receptor. In this particular embodiment, the potassium receptor comprises valinomycin, counter ion (Potassium tetrakis [3, 5- bis(trifluoromethyl)phenyl]borate), membrane (PVC) and plasticiser (DOS or NPOE).

[0140] The third working electrode 3c is configured to take potentiometric measurements and to produce a response when a liquid or liquid based sample comprising the bio-analyte potassium contacts the third reagent 4c.

[0141] A fourth reagent 4d is provided on the surface of the fourth working electrode 3d. The fourth reagent comprises a sodium receptor. In this particular embodiment, the sodium receptor comprises sodium ionophore VI, counter ion (sodium tetrakis [3,5- bis(trifluoromethyl)phenyl]borate), membrane (PVC) and plasticiser (DOS or NPOE).

[0142] The fourth working electrode 3d is configured to take potentiometric measurements and to produce a response when a liquid or liquid based sample comprising the bio-analyte sodium contacts the fourth reagent 4d.

[0143] By providing the sample testing device 1 with the capability of testing for both potassium and sodium in a liquid or liquid-based sample, the device may provide an indication of a user’s cardiovascular health. As albumin / creatinine ratio (P:CR) is widely acknowledged to be an indicator of several health outcomes including kidney health, chronic kidney disease, and cardiovascular health, this device may provide a more detailed overview of the patient’ s health.

[0144] A fifth reagent 4e is provided on the fifth working electrode 3e. The fifth reagent 4e comprises a pH detector reagent. In this particular embodiment, the pH detector reagent comprises hydrogen ionophore II, counter ion (sodium tetrakis [3,5- bis(trifluoromethyl)phenyl]borate) membrane (PVC) and plasticiser (DOS or NPOE). The fifth working electrode 3e is configured to take potentiometric measurements and to produce a response when a liquid or liquid based sample contacts the fifth reagent 4e to indicate the pH of the liquid or liquid-based sample.

[0145] A sixth reagent 4f is provided on the sixth working electrode 3f. The sixth reagent 4f comprises a haemoglobin receptor. In this particular embodiment, the haemoglobin receptor comprises carbon black, lithium perchlorate, phosphate buffer and saponin.

[0146] The sixth working electrode 3f is configured to take amperometric measurements and to produce a response when a liquid or liquid based sample comprising the bio-analyte haemoglobin contacts the sixth reagent 4f.

[0147] A seventh reagent 4g is provided on the seventh working electrode 3g. The seventh reagent comprises a glucose receptor. In this particular embodiment, the glucose receptor comprises glucose oxidase, ruthenium hexamine, trehalose, tween 20 and phosphate buffer. The skilled person will appreciate that in alternative embodiments a different glucose receptor may be provided. For example, an alternative glucose receptor may comprise glucose dehydrogenase and methylene blue.

[0148] The seventh working electrode 3g is configured to take amperometric measurements and to produce a response when a liquid or liquid based sample comprising the bio-analyte glucose contacts the seventh reagent 4g.

[0149] Each working electrode 3 configured to take amperometric measurements i.e. the second, sixth and seventh working electrodes 3b, 3f, 3g are grouped together in a consecutive series, and each working electrode configured to take potentiometric measurements i.e., the first, third, fourth and fifth working electrodes 3a, 3c, 3d, 3e are also grouped together in a consecutive series. Providing the working electrodes 3 in this particular configuration may help the working electrodes to be easily read as when the sample testing device 1 is read, for example by a test reader (not shown), the amperometric working electrodes 3b, 3f, 3g may form part of a separate circuit to the potentiometric working electrodes 3a, 3c, 3d, 3e. Furthermore, separating the amperometric working electrodes 3b, 3f, 3g from the potentiometric working electrodes 3a, 3c, 3d, 3e may minimise noise (e.g. from leakage currents) between each set of working electrodes 3.

[0150] The skilled person will appreciate that there may be additional working electrodes. For example, there may be an eighth working electrode provided with an eighth reagent. The eighth reagent may comprise a creatine receptor. The eighth reagent may be configured to take amperometric or chronoamperometric measurements and to produce a response when a liquid or liquid based sample comprising the bio-analyte creatine contacts the eighth reagent.

[0151] Each reagent 4 comprises at least one particulate configured to retain the reagent on the surface of the working electrode 3. The particulate is selected from the group consisting of: a montmorillonite clay, a silica-based particulate, and any combination thereof. In this embodiment, the montmorillonite clay is bentonite and the silica-based particulate is cabosil M5. Provision of such particulates may form structure on the surface of the working electrode 3, thereby assisting in the structural immobilisation of the reagent 4 close to the surface of the working electrode 3.

[0152] The sample testing device 1 also comprises a reference electrode 5 provided on the substrate 2. The reference electrode 5 is configured to provide a stable reference potential which may assist in improving the accuracy of the measurement of the potential of the or each working electrode 3. The reference electrode may be formed from any material selected from the group consisting of: silver / silver chloride and silver.

[0153] The sample testing device 1 comprises a counter electrode 6 provided on the substrate 2. The counter electrode 6 is configured to allow current from each working electrode 3 to flow through the cell without increasing the current flowing through the reference electrode 5. The counter electrode 6 may be formed from any material selected from the group consisting of: carbon, graphite, silver, gold, platinum, and any combination thereof.

[0154] The sample testing device 1 also comprises nine conductive tracks 7 provided on the substrate 2. Each conductive track 7 extends from a first end of the substrate 2a along the length of the substrate 2 and is connected to a corresponding working electrode 3 or reference electrode 5 or counter electrode 6 at a terminal end. In this way, each working electrode 3, the reference electrode 5, and the counter electrode 6 is connected to a single conductive track 7. Each conductive track 7 is formed from an electrically conductive material selected from the group consisting of: carbon, graphite, gold, silver, silver / silver chloride, and any combination thereof and is formed on the substrate 2 by at least one of screen-printing, sputter coating, or laser ablation.

[0155] The sample testing device 1 comprises a flow channel 8 which extends longitudinally. Seven sample chambers 9 extend laterally from the flow channel 8. Each working electrode 3 is housed in a corresponding sample chamber 9 at the end distal to the flow channel 8. Each sample chamber 9 is substantially rectangular and is delimited by at least one wall 10. Each sample chamber 9 has a depth of approximately 100 pm and a defined volume. This may help limit diffusion of each reagent away from the corresponding working electrode 3 during use. Furthermore, a high buffer concentration (where buffering agent is present) may be maintained in the immediate vicinity of the working electrode 3 thereby increasing its buffering capacity. This solution is preferable to adding an excess of acidic buffering agent, which may have other effects on the product performance such as slower dissolution of the reagent.

[0156] The sample testing device 1 comprises a cover 11 provided over each working electrode 3, the reference electrode 5 and the counter electrode 6. The cover 11 is formed from a hydrophilic material which in this embodiment is polyethylene terephthalate (PET).

[0157] Although not shown, the sample collection device 1 may comprise an outer housing which surrounds at least a portion of the sample collection device 1 and is formed from a rigid plastics material. This may act to protect the components of the sample testing device 1. The outer housing may comprise a gripping portion provided distal to each working electrode 3 to encourage the user to grip the sample testing device away from each working electrode 3 thereby minimising the risk of the user coming into contact with the liquid or liquid-based sample during use. At least one opening may be provided in the housing over each working electrode 3 such that the sample collection device 1 may be read by another device such as a test reader.

[0158] The sample testing device 1 is configured to receive a sample. In this embodiment, the sample is a liquid or liquid based sample selected from the group consisting of: urine, blood, and saliva. The liquid or liquid-based sample may comprise at least one target bio-analyte selected from the consisting of: a protein, creatinine, sodium, potassium, pH, haemoglobin, glucose, and any combination thereof.

[0159] In use the liquid or liquid based sample is released into the flow channel 8 via an opening proximal to an edge of the substrate 2. In some embodiments, the sample testing device 1 may comprise a sample storage portion (not shown) in liquid communication with each sample chamber 9 via the flow channel 8. The sample storage portion may be configured to at least temporarily store the liquid or liquid based sample as a stored liquid or liquid-based sample and may be actuable to release a fixed volume of the stored liquid or liquid-based sample. A barrier or valve or similar may be provided between the sample storage portion and the flow channel 8. The barrier or valve or similar may be moveable from a first position in which the barrier or valve or similar may block liquid communication between the sample storage portion and the flow channel 8, to a second position in which the barrier or valve or similar may allow liquid communication between the sample storage portion and the flow channel 8.

[0160] Once the liquid or liquid-based sample has been released into the flow channel 8, it is drawn into each sample chamber 9. As each sample chamber 9 has a depth of approximately 100 pm and a defined volume, at least a portion of the released liquid or liquid-based sample from the flow channel is efficiently transferred via capillary action into each sample chamber 9 such that the or each working electrode 3 is covered by the liquid or liquid based sample. As such, when the or each sample chamber 9 is full, no more liquid or liquid based sample is drawn in. This may help provide a still fluid within each sample chamber 9 which may assist in providing a stable measurement.

[0161] Each working electrode 3 is configured to produce a response when the liquid or liquidbased sample contacts the corresponding reagent 4. Each response may indicate whether the specific target bio-analyte to which the corresponding reagent 4 is directed is present within the liquid or liquid-based sample. Each response may indicate that the target bio-analyte to which the corresponding reagent 4 is directed is present within the liquid or liquid-based sample if the concentration of the target bio-analyte present is above a threshold value. The threshold value may be selected in accordance with the specific target bio-analyte to which the corresponding reagent 4 is directed, for example albumin or creatinine. The response may indicate the concentration of target bio-analyte present within the liquid or liquid-based sample.

[0162] The sample testing device 1 is configured to be received and read by a test reader (not shown). The test reader comprises a sensing portion having at least one sensor configured to read at least one working electrode 3. In this particular embodiment, the test reader comprises seven sensors which each correspond to a working electrode 3 of the sample testing device 1. The test reader stores seven reference curves which each correspond to a working electrode 3 and the specific target bio-analyte to which the corresponding reagent 4 is directed.

[0163] With reference now to Figure 2, a plot of current versus voltage is plotted for samples containing albumin in varying concentrations between 0 and 300 mg / L. To obtain such a graph, a liquid or liquid based sample comprising a known concentration of albumin contacts the first reagent 4a, and a differential pulsed voltage is applied to the first working electrode 3a. The corresponding current is then recorded, and the test is repeated using liquid or liquid based samples comprising different known concentrations of albumin. The current peaks of Figure 2 are then plotted against the known concentration of albumin within the sample as shown in Figure 3.

[0164] Figure 3 shows an example of a reference curve stored by the test reader corresponding to the first working electrode 3a and first reagent 4a, comprising the protein receptor. In use, once the liquid or liquid based sample has been released into the flow channel 8 and drawn into the first sample chamber 9, it contacts the first reagent 4a provided on the surface of the first working electrode 3a. The sample testing device 1 may then be inserted into the test reader whereby the sensing portion reads the response i.e., the current, of the first working electrode 3a. The reader then compares the response with the corresponding reference curve shown in Figure 3 and outputs a reading indicating whether albumin is present within the liquid or liquidbased sample, as well as outputting a reading corresponding to the concentration of albumin present in the sample based upon comparison with the reference curve of Figure 3.

[0165] With reference now to Figures 4 to 6, examples of reference curves corresponding to the third working electrode 3c, the fourth working electrode 3d, and the fifth working electrode 3e respectively are shown. Figure 4 shows an example of a reference curve stored by the test reader corresponding to the third working electrode 3c and third reagent 4c, comprising the potassium receptor.

[0166] Figure 5 shows an example of a reference curve stored by the test reader corresponding to the fourth working electrode 3d and fourth reagent 4d, comprising the sodium receptor.

[0167] Figure 6 shows an example of a reference curve stored by the test reader corresponding to the fifth working electrode 3e and the fifth reagent 4e comprising the pH detecting receptor.

[0168] In use, when the liquid or liquid based sample is released into the flow channel 8 and flows into each sample chamber 9, it contacts each of the third, fourth and fifth reagents 4c, 4d, 4e. The sample testing device 1 may be inserted into the test reader. As each of the third, fourth, and fifth working electrodes 3c, 3d, 3e are configured to take potentiometric measurements, the sensing portion reads the response i.e., potential, of each working electrode 3c, 3d, 3e and compares it with the corresponding reference curves shown in Figures 4 to 6. The test reader then outputs a reading indicating whether potassium and sodium are present within the liquid or liquid based sample, as well as outputting a reading corresponding to the concentration of potassium and sodium present in the sample based upon comparison with the reference curves of Figures 4 and 5 respectively. The test reader also outputs a reading indicating the pH of the liquid or liquid based sample based upon comparison of the reading of the fifth working electrode 3e with the reference curve of Figure 6.

[0169] With reference now to Figures 7 to 9, examples of reference curves corresponding to the second working electrode 3b, the sixth working electrode 3f, and the seventh working electrode 3g respectively are shown.

[0170] Figure 7 shows an example of a reference curve stored by the test reader corresponding to the second working electrode 3b and second reagent 4b, comprising the creatinine receptor.

[0171] Figure 8 shows an example of a reference curve stored by the test reader corresponding to the sixth working electrode 3f and sixth reagent 4f, comprising the haemoglobin receptor.

[0172] Figure 9 shows an example of a reference curve stored by the test reader corresponding to the seventh working electrode 3g and seventh reagent 4g, comprising the glucose receptor.

[0173] In use, when the liquid or liquid based sample is released into the flow channel 8 and flows into each sample chamber 9, it contacts each of the second, sixth and seventh reagents, 4b, 4f, 4g. The sample testing device 1 may be inserted into the test reader. As each of the second, sixth and seventh working electrodes 3b, 3f, 3g are configured to take amperometric measurements, the sensing portion reads the response i.e., current, of each working electrode 3b, 3f, 3g and compares it with the corresponding reference curves shown in Figures 7 to 9. The test reader then outputs a reading indicating whether creatinine, haemoglobin, and glucose are present within the liquid or liquid based sample, as well as outputting a reading corresponding to the concentration of creatinine, haemoglobin, and glucose present in the sample based upon comparison with the reference curves of Figures 7, 8, and 9 respectively.

[0174] The reader is also configured to output calibrated readings, for example the test reader may output each reading relative to the creatinine reading. This enables users to obtain an albumin to creatinine ratio which provides a more accurate measure of albumin concentration as the concentration of creatinine may correct for the concentration of urine when the sample is taken, for example.

[0175] The skilled person will appreciate that the reference curves shown in Figures 4 to 9 are merely examples provided as evidence of proof of concept and alternative curves may also be used in practice. For example, Figures 10 to 19 show a number of alternative reference curves which may also be used in practice. Figure 10 shows another example of a reference curve stored by the test reader corresponding to the third working electrode 3c and third reagent 4c, comprising the potassium receptor is shown. This reference curve was obtained using potentiometric measurements of eight pooled urine samples spiked with potassium of known concentration. The log calibration model R2is 0.98.

[0176] Figure 11 shows another example of a reference curve stored by the test reader corresponding to the fifth working electrode 3e and the fifth reagent 4e comprising the pH detecting receptor. This reference curve was obtained using potentiometric measurements of four pooled urine samples adjusted by HCl / NaOH titration to pH0.5 intervals. The linear calibration model R2is 0.96.

[0177] Figure 12 shows another example of a reference curve stored by the test reader corresponding to the second working electrode 3b and second reagent 4b, comprising the creatinine receptor. In this example, the creatinine receptor comprised an enzymatic receptor comprising a 3-enzyme cascade of creatinase, creatininase, and sarcosine oxidase. The enzymatic receptor also comprised a ferricyanide mediator. The second working electrode comprised a carbon electrode and a cover without a vent. This reference curve was obtained using chronoamperometric measurements of two pooled urine samples spiked with creatinine of known concentration. The linear calibration model R2is 0.88.

[0178] Figure 13 shows another example of a reference curve stored by the test reader corresponding to the second working electrode 3b and second reagent 4b, comprising the creatinine receptor. In this example, the creatinine receptor comprised an enzymatic receptor comprising a 4-enzyme cascade of creatinase, creatininase, sarcosine oxidase, and horseradish peroxidase. The enzymatic receptor also comprised a ferrocyanide mediator. The second working electrode comprised a carbon electrode and a cover with a vent. This reference curve was obtained using chronoamperometric measurements of two pooled urine samples spiked with creatinine of known concentration. The linear calibration model R2is 0.99.

[0179] Figure 14 shows another example of a reference curve stored by the test reader corresponding to the second working electrode 3b and second reagent 4b, comprising the creatinine receptor. In this embodiment, the creatinine receptor comprised an enzymatic receptor comprising a 3-enzyme cascade of creatinase, creatininase, and sarcosine oxidase. The second working electrode was a Prussian blue electrode comprising a cover having an air vent to allow oxygen from the surroundings to drive the sarcosine oxidase reaction. This reference curve was obtained using chronoamperometric measurements of a urine sample spiked with creatinine of known concentration. The polynomial calibration model R2is 0.97.

[0180] Figure 15 shows another example of a reference curve stored by the test reader corresponding to the sixth working electrode 3f and sixth reagent 4f, comprising the haemoglobin receptor. This reference curve was obtained using chronoamperometric measurements of samples pooled from duplicate donations, spiked with haemoglobin of known concentration. The test reader may be configured to output a binary signal indicating whether the sample contains a concentration of urinary haemoglobin above or below a threshold value, for example, a threshold value of 5nM. The logarithmic calibration model R2is 0.7.

[0181] Figure 16 shows another example of a reference curve stored by the test reader corresponding to the seventh working electrode 3g and seventh reagent 4g, comprising the glucose receptor. This reference curve was obtained using chronoamperometric measurements of three pooled samples spiked with glucose of known concentration. The linear calibration model R2is 0.99.

[0182] Figure 17 shows another example of a reference curve stored by the test reader corresponding to the fourth working electrode 3d and fourth reagent 4d, comprising the sodium receptor. This reference curve was obtained using potentiometric measurements of four pooled urine samples spiked with sodium of known concentration. The log calibration model R2is 0.97.

[0183] Figure 18 shows another example of a reference curve stored by the test reader corresponding to the first working electrode 3a wherein the first reagent 4a comprises a protein receptor. In this example, the protein receptor is a total protein receptor. This reference curve was obtained using chronoamperometric measurement of a urine sample spiked with protein of known concentration. The polynomial calibration model R2is 0.96.

[0184] Figure 19 shows another example of a reference curve stored by the test reader corresponding to the first working electrode 3a wherein the first reagent 4a comprises a protein receptor. In this example, the protein receptor is a total protein receptor. This reference curve was obtained using differential pulse voltametric measurement of a urine sample spiked with protein of known concentration. The polynomial calibration model R2is 0.89.

Claims

CLAIMS1. A sample testing device comprising: at least one working electrode; and a reagent dried on and / or adjacent to the surface of the working electrode; wherein the reagent comprises a protein receptor comprising copper and / or a copper salt, and an acidic buffering agent.

2. The sample testing device of claim 1 wherein the protein receptor is an albumin receptor.

3. The sample testing device of claim 1, wherein the copper salt is a copper (II) salt.

4. The sample testing device of claim 3, wherein the copper (II) salt is at least one of copper sulphate (CuSCL) or copper chloride (CuCh).

5. The sample testing device of any preceding claim, wherein the acidic buffering agent is an agent conferring a pKa of between 3.0 and 8.0.

6. The sample testing device of any preceding claim, wherein the acidic buffering agent is at least one agent selected from the group consisting of: acidified phosphate buffer, MES buffer, sodium acetate, L-tartaric acid, maleic acid, and any combination thereof.

7. The sample testing device of any preceding claim, wherein the reagent comprises at least one film forming agent and / or at least one copper chelating agent, and wherein the at least one film forming agent and / or at least one copper chelating agent is selected from the group comprising: sodium gluconate, citrate, EDTA, and any combination thereof.

8. The sample testing device of any preceding claim, wherein the reagent comprises at least one particulate configured to retain the reagent on the surface of the working electrode.

9. The sample testing device of claim 8, wherein the at least one particulate is selected from the group consisting of: a montmorillonite clay, a silica-based particulate, and any combination thereof.

10. The sample testing device of any preceding claim further comprising a substrate.

11. The sample testing device of claim 10 further comprising a reference electrode and a counter electrode provided on the substrate.

12. The sample testing device of claim 11 further comprising at least one conductive track provided on the substrate.

13. The sample testing device of claim 12 wherein each of the at least one working electrode, reference electrode and counter electrode are connected to a corresponding conductive track.

14. A sample testing device comprising: at least a first working electrode and a second working electrode; and at least a first reagent and a second reagent; wherein the first reagent is provided on and / or adjacent to the surface of the first working electrode and the second reagent is provided on and / or adjacent to the surface of the second working electrode, wherein the first reagent comprises a protein receptor and the second reagent comprises a creatinine receptor, the creatinine receptor comprising an enzymatic receptor.

15. The sample testing device of claim 14, wherein the enzymatic receptor comprises creatininase, creatinase, sarcosine oxidase, and / or horseradish peroxidase.

16. The sample testing device of any one of claims 14 or 15, wherein the first reagent is dried on and / or adjacent the surface of the first working electrode.

17. The sample testing device of any one of claims 14-16, wherein the protein receptor comprises copper and / or a copper (II) salt.

18. The sample testing device of claim 17, wherein the copper (II) salt is at least one of copper sulphate (CuSCh) or copper chloride (CuCl).

19. The sample testing device of any one of claims 14-18, wherein the protein receptor comprises an acidic buffering agent.

20. The sample testing device of any one of claims 14-19, further comprising a substrate and at least one conductive track provided thereon.

21. The sample testing device of any one of claims 14-20, further comprising a third working electrode wherein a third reagent is provided on the surface of the third working electrode, and the third reagent comprises a potassium receptor.

22. The sample testing device of claim 21, further comprising a fourth working electrode wherein a fourth reagent is provided on the surface of the fourth working electrode, and the fourth reagent comprises a sodium receptor.

23. The sample testing device of any one of claims 14-22, further comprising at least two sample chambers wherein each working electrode is provided in a corresponding sample chamber.

24. The sample testing device of claim 23, further comprising a flow channel wherein each sample chamber extends from the flow channel.

25. A test reader configured to read the sample testing device of any preceding claim, the test reader comprising a sensing portion having at least one sensor configured to read at least one working electrode of a sample testing device.

26. The test reader of claim 25 wherein the number of sensors is selected in accordance with the number of working electrodes of the sample testing device.

27. The test reader of any one of claim 25 or 26, wherein the test reader uses differential pulse voltammetry (DPV) and / or chronoamperometry to read the at least one working electrode of the sample testing device.

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