METHOD FOR PREPARING A WORKING ELECTRODE

Abstract

The present invention relates to a method for the preparation of a working electrode, the method comprising application of a sensing material in several steps. Further, the present invention relates to an analyte sensor comprising the working electrode as well as to the use of the analyte sensor for detecting at least one analyte in a sample.

Claims

1. A method for manufacturing a working electrode of an analyte sensor is provided, wherein the method comprises the following steps: (a) providing a substrate comprising a first side and a second side, at least one conductive material positioned on the first side of the substrate, (b) applying a sensing material to an application area on the first side of the substrate, and (c) obtaining the working electrode of the analyte sensor on the first side of the substrate, wherein the sensing material comprises at least one enzyme and at least one cross-linker, wherein the sensing material is applied in step (b) in a wet layer thickness of greater than about 20 μm in a single application, wherein step (b) is carried out via cannula-coating.

2. The method of claim 1, wherein step (b) is performed only once.

3. The method of claim 1, wherein the at least one conductive material positioned on the first side of the substrate is selected from gold, carbon, carbon paste and any combination thereof.

4. The method of claim 1, wherein the sensing material comprises at least chemical crosslinker, particularly PEGDGE 500.

5. The method of claim 1, wherein the at least one crosslinker is present in the sensing material in an amount up to about 25% (w/w), particularly of about 0.5% (w/w) to about 25% (w/w) based on the dry weight of the sensing material.

6. The method of claim 1, wherein (i) the cannula has an inner diameter of about 0.3 mm to about 0.4 mm, particularly about 0.33 mm; and/or (ii) the speed of the substrate relative to the cannula during step (b) is in the range from about 1 mm/s to about 20 mm/s, particularly in the range from about 2 mm/s to about 15 mm/s, e.g. about 8 mm/s, and/or (iii) the flow rate of the sensing material during step (b) is in the range from about 0.007 ml/min to about 0.05 ml/min, preferably in the range from about 0.01 ml/min to about 0.03 ml/min, particularly of about 0.015 ml/min, and/or (iv) the distance between the cannula and the surface of the first side of the substrate to which the sensing material is applied during step (b) is in the range from 50 μm to about 100 μm, particularly about 70 μm.

7. The method of claim 1, wherein after step (b) the sensing material is dried.

8. The method of claim 1, wherein after drying the sensing material of the working electrode has a dry total thickness in the range from about 3 μm to about 8 μm, particularly from about 3 μm to about 6 μm and more particularly from about 4 μm to about 5 μm.

9. The method of claim 1, which is carried out continuously, particularly wherein the substrate is a raw substrate material, particularly a sheet or a roll onto which the layer of sensing material is applied.

10. A method for manufacturing an analyte sensor comprising manufacturing a working electrode according to claim 1 and providing at least one further electrode.

11. An analyte sensor comprising: (i) a substrate comprising a first side and a second side, and at least one conductive material positioned on the first side of the substrate, (ii) a working electrode comprising a sensing material, which at least partially covers the first side of the substrate, wherein the sensing material forms a layer on the first side of the substrate, wherein the layer of sensing material comprises edges generated by the application of the sensing material onto an application area on the substrate, wherein the sensing material comprises at least one enzyme and optionally at least one crosslinker, wherein the layer of sensing material has a dry average total thickness in the range from about 3 μm to about 8 μm, particularly from about 3 μm to about 6 μm and more particularly from about 4 μm to about 5 μm, and wherein the dry total thickness of the layer of sensing material along at least one of said edges is substantially the same or is increased compared to the dry average total thickness of the layer of the sensing material.

12. The analyte sensor of claim 11, wherein the dry total thickness of the sensing material at least along one of the edges of the application area, particularly along all edges of the application area, is at least about 75% and up about 125% compared to the dry average total thickness of the layer of the sensing material (being defined as 100%), or wherein the dry total thickness of the sensing material at least along one of the edges of the application area, particularly along all edges of the application area, is at least about 125% compared to the dry average total thickness of the layer of the sensing material (being defined as 100%).

13. The analyte sensor of claim 11 comprising at least one further electrode, particularly precisely one further electrode, particularly wherein the at least one further electrode is selected from a counter electrode, a reference electrode and a combined counter/reference electrode.

14. The analyte sensor of claim 11, which is a two-electrode sensor comprising precisely one working electrode and precisely one combined counter/reference electrode.

15. Use of an analyte sensor of claim 11 for detecting at least one analyte in a sample.

Description

DESCRIPTION OF THE FIGURES

[0225] FIG. 1 shows a schematic depiction of a working electrode of the present invention.

[0226] FIG. 2 shows a topographic measurement of the dry total thickness of a working electrode of the prior art.

[0227] FIG. 3 shows the course of the sensitivity over time for a working electrode of the prior art.

[0228] FIG. 4 shows a topographic measurement of the dry total thickness of a working electrode of the present invention.

[0229] FIG. 5 shows the course of the sensitivity over time for a working electrode of the present invention.

[0230] FIG. 1 shows an embodiment of a working electrode comprising a sensing material layer prepared in a single application step with a wet layer thickness of more than 20 μm. An analyte sensor 124 comprises a sensor substrate 114 having a first side 120. The first side 120 comprises at least one conductive material 111 comprising more preferably two materials, e.g. gold and/or carbon. Specifically, the conductive material may comprise a layer of gold 112 and a layer of a further material 110, for example carbon. A sensing material layer 118 applied in a single step onto the conductive material 111 positioned on the first side 120 of the sensor substrate 114 and subsequently dried is shown. The sensing material layer 118 covers at least a portion of the conductive material 111. At the edges 121a and 121b, a substantial increase in the dry total thickness 125a, i.e. in a section spanning a distance of 10 μm from the outermost boundary of the sensing material layer 118 inward, a substantial increase in the dry total thickness 125a compared to the dry average total thickness of the sensing material layer 118 and also to the total dry total thickness 125b in the central section, i.e. a 10 μm section spanning a distance around the center of the sensing material layer 118, is observed.

[0231] In a further embodiment of the invention (not shown), the dry total thickness at the edges may be substantially the same as the dry average total thickness of the sensing material layer.

[0232] The analyte sensor 124 is an electrochemical sensor comprising at least one electrode and respective circuitry. More particularly, the analyte sensor 124 is an amperometric electrochemical sensor comprising the at least one working electrode. Typically, the analyte sensor 124 comprises at least one further electrode, particularly a counter electrode and/or a reference electrode and/or a combined counter/reference electrode. The working electrode may be sensitive for the analyte to be measured at a polarization voltage which may be applied between working and reference electrodes and which may be regulated by a potentiostat. A measurement signal may be provided as an electric current between the counter electrode and the working electrode. A separate counter electrode may be absent and a pseudo reference electrode may be present, which may also work as a counter electrode. Thus, an analyte sensor 124 typically may comprise a set of at least two or a set of three electrodes. Specifically, the sensing material 118 is present in the working electrode 122 only.

[0233] The invention is not limited to one of the embodiments described above, but is modifiable in a great variety of ways. Those skilled in the art recognize that the embodiments according to the invention can easily be adapted without departing from the scope of the invention. Thus, simple adaptations are conceivable for the preparation of the analyte sensor. The invention enables the preparation of an analyte with reproducible sensor sensitivity at reduced production costs. Further characteristics, details and advantages of the invention follow from the wording of the claims and from the following description of practical examples based on the drawings.

[0234] The content of all literature references cited in this patent application is hereby included by reference to the respective specific disclosure content and in its entirety.

EXAMPLES

[0235] The following examples serve to illustrate the invention. They must not be interpreted as limiting with regard to the scope of protection.

Example 1: Preparation of a Sensing Material Layer of the Prior Art on a Working Electrode According to the Prior Art

[0236] A sensor substrate based on polyethylene terephthalate and a thin layer of gold was coated with a carbon paste via doctor blading. Suitable Carbon conductive inks are available from Ercon, Inc. (Wareham, Mass.), E.I. du Pont de Nemours and Co. (Wilmington, Del.), Henkel AG & Co. KGaA, Emca-Remex Products (Montgomeryville, Pa.), or TEKRA, A Division of EIS, Inc (New Berlin, Wis.). Afterwards, the carbon paste was dried for 12 h at 50° C.

[0237] A layer of sensing material was applied on the sensor substrate by cannula-coating (cannula 1.6 mm (inner diameter), flow rate 0.03 ml/min, speed 8 mm/s, distance between cannula and substrate 30 μm). The sensing material was dried for 3 minutes at 22° C. It was applied in three layers, each with a wet layer thickness of 30 μm.

[0238] The sensing material comprised 57% by weight of a polymeric transition metal complex (modified poly (vinylpyridine) backbone loaded with poly(biimidizyl) Os complexes covalently coupled through a bidentate linkage), 33% by weight of glucose oxidase and 10% by weight of PEG-DGE (poly(ethylene glycol)-diglycidylether) in each case based on the sum of the percentages by weight of the polymeric transition metal complex, glucose oxidase and PEG-DGE. Water was used as solvent. The total concentration of the polymeric transition metal complex, glucose oxidase and PEG-DGE in water was 50 mg/ml.

[0239] After drying, a reduced thickness due to spillage at the edges of the sensing material layer was found by a topography measurement on the sensor. The thickness of the sensing material layer was 0-4 μm at the edges being significantly lower than in the in the center region as shown in FIG. 2.

[0240] The reduced thickness at the edges has a negative effect on the sensor stability as shown in FIG. 3 by a substantial decrease in the current.

Example 2: Preparation of a Sensing Material Layer on a Working Electrode According to the Present Invention

[0241] A sensor substrate coated with gold and carbon paste was prepared as described in Example 1.

[0242] The sensing material of Example 1 was used.

[0243] A layer of sensing material was applied on the sensor substrate by cannula-coating (cannula 0.33 mm (inner diameter), flow rate 0.015 ml/min, speed 8 mm/s, distance between cannula and substrate 70 μm). The sensing material was dried for 3 minutes at 22° C.

[0244] FIG. 4 shows a topography measurement on a sensor after application of the sensing material. A substantially increased thickness at the edges of the sensing material was found.

[0245] The increased thickness at the edges has a positive effect on the sensor stability as shown in FIG. 5 by a substantially constant current.

Example 3: Variation of Dry Layer Thickness

[0246] A sensor substrate coated with gold and carbon paste was prepared as described in Example 1.

[0247] The sensing material of Example 1 was used.

[0248] The sensing material was applied to the substrate and the dry layer thickness was varied. The sensor drift was determined for the different sensors in a 180 mg/ml solution of glucose, buffered with phosphate over a time range of 14 days. Table 1 shows the average drift per day in % for the different dry layer thicknesses.

TABLE-US-00001 TABLE 1 dry layer thickness drift % per day 0.5 μm −20.0 1.2 μm −5.0 2.5 μm −0.7 4.0 μm −0.1

[0249] The sensor drift is an indicator of the change in sensitivity of the sensor. It can be seen that a dry layer thickness of 2.5 μm or less leads to a significantly increased drift.