WO2004029609A1

WO2004029609A1 - Heat-sealed protective film for electrochemical sensors

Info

Publication number: WO2004029609A1
Application number: PCT/GB2003/004187
Authority: WO
Inventors: Seamus Patrick John Higson
Original assignee: Microarray Limited
Priority date: 2002-09-28
Filing date: 2003-09-27
Publication date: 2004-04-08
Also published as: GB0222567D0; AU2003269208A1

Abstract

ABSTRACTThere is disclosed an analytical device comprising: a substrate; analyte detection means disposed upon said substrate; and a protective film disposed over at least a portion of the analyte detection means; in which the protective film is heat sealed to the substrate so as to be partially or wholly removable by peeling.

Description

HEAT- SEALED PROTECTIVE FILM FOR ELECTROCHEMICAL SENSORS

This invention relates to analytical devices, methods of packaging analytical devices, and methods of preparing analytical devices for use. Particular, but by no means exclusive, reference is made to sensor devices.

There are a large number of commercially available sensors suitable for a wide range of applications. Examples of such sensors include biosensor strips, chemical sensor strips and analytical test strips, which may be of a chemical or biochemical nature.

Such sensors might be, for example, electrochemical and/or enzymatic in nature, or might contain immobilised chemical reagents.

Traditionally, such sensors are packaged in a foil or plastic package, with closure of the package being effected with an adhesive seal and/or a lacquer film. There are a number of significant disadvantages associated with such methods. Firstly, the use of adhesive in the presence of sensors is not desirable because, in general, the sensors require clean and uncontaminated conditions. Secondly, the prior art techniques are expensive inter alia because foil is an expensive material. In fact, packaging can comprise up to 40% of the total cost of some commercially available sensors. Thirdly, these prior art techniques are slow.

US 5,421,981 discloses an electrochemical sensor which is enclosed within a hermetically sealed envelope of a gas impermeable material. US 6,153,070 discloses sensor packaging for an ion sensitive field effect transistor comprising a housing having an aperture therein. The aperture is filled with a plug which is heat sealed into place. US 5,759,365 discloses an electrochemical sensor having a base plate which is permanently mated with a solid lid by heat sealing. When mated together in this way, the lid in conjunction with the base forms a capillary space into which a fluid sample may be drawn. Thus, the lid is part of the device itself, and not packaging therefor.

The present invention overcomes the above ment ied disadvantages associated with the prior art.

According to a first aspect of the invention there is provided an analytical device comprising:

a substrate; analyte detection means disposed upon said substrate; and a protective film disposed over at least a portion of the analyte detection means; in which the protective film is heat sealed to the substrate so as to be partially or wholly removable by peeling.

Such devices are conveniently unpackaged, economic to produce and highly amenable to mass production techniques. Furthermore, high quality packaging can be provided, affording excellent protection to the analytical device.

The protective film may be a flexible film.

The protective film may be polymeric (such as a polycarbonate, polyester or nylon film) or a foil, preferably a polymer coated foil.

The protective film may be partially or wholly removable from the substrate with a peel force of less than 50 N (5kg equivalent), preferably less than ION (1kg equivalent). This can be contrasted with the permanently fixed lid of US 5,759,364. The protective film may be heat sealed along a continuous boundary so as to completely enclose a portion of the substrate. Again, this can be contrasted with the permanently fixed lid of US 5,759,364, which is configured to define a capillary space into which a fluid sample is drawn. The protective film may be hermetically sealed to the substrate. In this way the integrity of the analyte sensing means can be maintained. For example, the analyte detection means might be protected from the ingress of moisture from the environment, and/or moisture might be entrapped by the film so as to maintain the analyte detection means at a defined humidity.

The substrate may comprise a strip.

The protective film may be substantially transparent. This enables convenient viewing of the analyte detection means.

Alternatively, the protective film is substantially opaque. This arrangement can be used to protect the analyte detection means from exposure to light.

The substrate may comprise a polymeric, ceramic or metallic material.

The protective film may comprise a tab portion which facilitates the peeling of the protective film from the substrate.

A portion of the protective film may be permanently attached to the substrate. In this way, partial removal of the protective film by peeling is conveniently effected. The permanent attachment may be effected by heat sealing.

The analytical device may comprise a sensor device, in which instance the analyte detection means comprises analyte sensing means. A sensor device might be a biosensor or a chemical sensor. Examples of sensor devices according to the invention include enzymatic, electrochemical, optical, conductimetric, chemical and biological sensor devices. Other examples of analytical devices are analytical test kits, analytical test strips either of a chemical or biochemical nature, and reagent kit devices such as biological reagent kits and analytical reagent kits. Examples of biological reagent kits include hygiene monitoring kits, ATP detectors, immunosensor kits, pregnancy testing kits and biological affinity kits such as antibody containing kits. Examples of analytical reagent kits include agrisensors, sensors for process and industrial control, pharmaceutical sensors and chemical sensors. A sensor device may comprise a DNA sensor and/or a "lab on a chip" type device in which one or more analyte sensing means is formed on an integrated circuit.

Analyte sensing means may comprise electrodes, or other means to facilitate an analysis. Electrodes might in this context be used for an electrochemical sensing process via, for example, amperometric, voltammetric, impedimetric or conductimetric means.

The analyte detection means may comprise one or more reagents which participate in a reaction with an analyte thereby allowing identification of the analyte. Examples of such systems include pregnancy testing kits and chemical sensors. The reagents may be immobilised on a surface of a storage area, such as a pad, may be impregnated with the reagents.

According to a second aspect of the invention there is provided a method of preparing an analytical device according to the first aspect of the invention for use comprising the step of:

peeling the protective film from the substrate so as to either partially or wholly remove the film from the substrate thereby exposing at least a portion of the analyte detection means. According to a third aspect of the invention there is provided a method of packaging an analytical device comprising the steps of:

providing an analytical device comprising a substrate and analyte detection means disposed on said substrate; heat sealing a protective film onto said substrate so that i) the protective film is disposed over at least a portion of the analyte detection means and ii) the protective film is partially or wholly removable from the substrate by peeling.

The protective film may be a flexible film.

The heat sealing of the protective film may permit partial or whole removal of the protective film from the substrate with a peel force of less than 50 N, preferably less than IO N.

The protective film may be heat sealed along a continuous boundary so as to completely enclose a portion of the substrate. The protective film may be hermetically sealed to the substrate.

The substrate may comprise a strip.

The method may further comprise the step of permanently attaching a portion of the protective film to the substrate.

The analytical device may be a sensor device, which may comprise a biosensor or chemical sensor. In this instance, the analyte detection means comprises analyte sensing means, which may comprise electrodes. The analyte detection means of the analytical device may comprise one or more reagents, which participate in a reaction with an analyte thereby allowing identification of the analyte.

Analytical devices in accordance with the invention will now be described with reference to the accompanying drawings, which:

Figure 1 shows (a) a plan view of a first embodiment of a sensor device and (b) a cross sectional view along the line A - A¹ of (a);

Figure 2 is a plan view of a second embodiment of a sensor device;

Figure 3 is a plan view of a third embodiment of a sensor device;

Figure 4 is a plan view of the fourth embodiment of a sensor device;

Figure 5 shows a heat sealing process; and

Figure 6 is a plan view of an analytical device.

Figure 1 shows a first embodiment of a sensor device 10 of the invention comprising a substrate 11, electrodes 12, 14, electrode connections 16, 18 and a protective film 20 disposed upon the substrate 10. The protective film 20 is secured to the substrate 11 by heat sealing, the heat sealing process being performed so that the protective film 20 is easily removed from the substrate by an able bodied user by peeling the film 20 away from the substrate 11 with their fingers. The protective film 20 is heat sealed to the substrate 11 at the boundary 20a of the film 20, the heat sealed region being depicted by hatches in Figure 1. The electrodes 12, 14 can be of any suitable material, typically a metal but possibly comprising, or consisting of, graphite, a conducting polymer or another substantially conductive material. The substrate 11 might be fabricated from a ceramic material, a polymer (such as polyester) or any suitable material which, in this embodiment, should be substantially non-conductive. The fabrication of such sensor devices without the protective film 20 is well known in the art and therefore further details are not provided herein.

In use, the protective film 20 is simply peeled away by a user, to expose the sensing electrodes 12, 14. Before such use the protective film 20 protects the electrodes 12, 14 from degradation by shielding the electrodes from dirt, moisture and other detrimental environmental contaminants.

Figure 2 shows a second embodiment of a sensor device 22 which has substantial similarity with Figure 1. Thus, identical numerals are to denote elements which are shared between Figure 1 and Figure 2. The sensor device 22 further comprises a tab portion 24. The tab portion 24 is part of the protective film 20 but is not heat sealed to the substrate 11. The tab portion 24 is easily raised and grasped by the user of sensor device 22, and thus facilitates the removal of the protective film 20.

Figure 3 depicts a third embodiment of a sensor device 30. Again, many elements are shared with the first and second embodiments, and identical numerals are used to denote such shared features. The protective film 20 of the sensor device 30 comprises a portion 32 which is permanently sealed to the substrate 11. The portion 30 is illustrated in Figure 3 by way of colouring out the portion 30 so as to be opaque to UV or visible light. The permanently sealed portion 30 permits partial, rather than total removal of the film 20 by a user, with the film 20 remaining after peeling, attached to the substrate 11 via the portion 30. The permanent attachment of the portion 30 to the substrate is conveniently achieved by suitable heat sealing treatment, as explained in more detail below. However, other attachment techniques, such as bonding with an adhesive, might be contemplated.

Figure 4 depicts a fourth embodiment of a sensor device 40. Identical numerals are used to denote features shared with the first, second and third embodiments.

In contrast to Figures 1 to 3, in which a subset of the surface of the substrate 11 is covered by the film 20, in Figure 4 substantially the entire surface of the substrate 11 is covered by the protective film 20.

Heat sealing techniques per se are well known in a number of application areas, such as, for example, packaging of foodstuffs. In the present invention, the protective film is heat sealed to the substrate of the sensor device by bringing the portions of the film which are intended to be heat sealed into contact with the substrate at elevated temperatures, typically under conditions of heat and pressure. Attachment of the film to the substrate can be achieved by melting the surface of the film onto the substrate, with attachment occurring once the film solidifies. Additionally, or alternatively, the film may be coated with a lacquer which is activated by the heat sealing process. Such techniques, materials suitable for use with such techniques, are well known to those skilled in the art. The film might be a polymer, such as a polycarbonate, polyester or nylon, or another material, such as a foil. In any event, it is preferred that the film is flexible, since such films are the most convenient from the point of view of handling prior to heat sealing, and in terms of convenient removal from the substrate.

In a convenient, but non-limiting, embodiment, heat sealing is performed using a hot stamping process. Such a process is depicted in Figure 5, which shows a hot stamp 50 disposed above a film 52. The film 52 is itself disposed above a substrate 54 which has formed thereon a number of sensor elements 56. The hot stamp 50 is brought down onto the film 52, forcing the film 52 onto the substrate 54. The hot stamp 50 is shaped so that, with the film 52 in contact with the substrate 54, contact is only made between hot stamp 50 and film 52 in the regions of the substrate where a heat seal with the film 52 is intended. The temperature of the hot stamp 50, the application pressure and the contact time of the hot stamp 50 and the film 52 are controlled so that the film 52 is securely sealed to the substrate 54, but not so strongly that the film 52 cannot be conveniently removed by peeling. The precise nature of these conditions will be dependent on the precise nature of the substrate and film utilised, but can be deduced easily by those skilled in the art. Preferably, the peel force required to remove the protective film is less than 50 N, more preferably less than IO N, most preferably less than 5 N.

The heat sealing process shown in Figure 5 results in film being heat sealed around each sensor unit 56. Subsequently, the individual sensor devices can be produced by dividing the substrate by sawing, dicing or like treatment. In this way, an economy of scale is achieved with concomitant reductions in packaging costs.

Permanently sealed portions of the protective film, such as the portion 30 shown in Figure 3, can be conveniently produced by appropriate adjustment of the heat sealing conditions, eg, heat and pressure may be applied for a longer period of time in these regions.

Hermetic sealing of the film to the substrate improves the protection afforded to the analyte sensing means contained within the protective film. If the protective film is a polymer, hermetic sealing can be improved by metallising a side of the film. Alternatively, the use of foil as the protective film is another possibility.

The invention is not limited to sensors which comprise electrodes. Other types of analytical device, for example light sensitive devices, biological reagent kits or strips and analytical reagent kits or strips, might be packaged using the principles described herein. Reagent kits might comprise a reagent, such as a bio-reagent, deposited onto the substrate by a technique such as screen printing, stencil printing or ink jet deposition. Alternatively, immobilisation or impregnation techniques might be used to secure a reagent to a sensor. In one known type of sensor, a strip .(typically of ca. 4cm length) is provided having at one end a pad which is impregnated with suitable reagents. Prior art packaging techniques involve wrapping foil around the entire strip, even though the active sensing portion (ie, the pad) comprises only a small proportion of the overall device. The reason for this is that water evaporates from the pack, and thus after removal of the foil wrapping, the pad is wetted with a solution prior to use. The strip is of ca. 3 to 4cm length so that it can be picked up for wiping with the solution. Foil wrapping along the entire length of the strip is clearly more expensive than wrapping around the much smaller portion of the strip which houses the pad, since more material is required. However, it is not possible to wrap around a portion of the strip using the prior art techniques, because it is not possible to seal the foil against the strip.

The present invention provides improved packaging of such analytical devices. Figure 6 shows an embodiment of an analytical device 60 comprising a strip substrate 62 having disposed thereon a pad 64 which is impregnated with reagents. The device 60 further comprises a protective film 66 which is heat sealed to the strip substrate 62 in the hatched portions 66a.

It should be noted that the film 66 is only applied to a relatively small portion of the strip 62, at the end of the strip 62 where the pad 64 is disposed, thereby minimising the amount of film required to adequately package the device. Since the film 66 can provide a hermetic seal to the strip 62, it may prove to be unnecessary to treat the pad with a solution prior to use. Thus, it may be possible to reduce the length of the strip 62, thereby providing further economies in the amount of materials required to produce a sensor device. Further variations are possible. For example, it is possible to provide an optically opaque protective film, for example to protect the reagents, absorbent pads or other components from light. Alternatively, the protective film may be optically transparent, thereby facilitating viewing of the underlying analyte detection means, such as underlying electrodes, absorbent pads, immobilised reagents or other components.

Claims

An analytical device comprising:

a substrate; analyte detection means disposed upon said substrate; and a protective film disposed over at least a portion of the analyte detection means;

in which the protective film is heat sealed to the substrate so as to be partially or wholly removable by peeling.

2. A device according to claim 1 in which the protective film is a flexible film.

3. A device according to claim 2 in which the protective film is polymeric.

4. A device according to claim 2 in which the protective film is a foil.

5. A device according to any of claims 1 to 4 in which the protective film is partially or wholly removable from the substrate with a peel force of less than IO N.

6. A device according to any of the previous claims in which the protective film is heat sealed along a continuous boundary so as to completely enclose a portion of the substrate.

7. A device according to claim 6 in which the protective film is hermetically sealed to the substrate.

8. A device according to any of the previous claims in which the substrate comprises a strip.

9. A device according to any of the previous claims in which the protective film is substantially transparent.

10. A device according to any of claims 1 to 8 in which the protective film is substantially opaque.

11. A device according to any of the previous claims in which the substrate comprises a polymeric, ceramic or metallic material.

12. A device according to any of the previous claims in which the protective film comprises a tab portion which facilitates peeling of the protective film from the substrate.

13. A device according to any of the previous claims in which a portion of the protective film is permanently attached to the substrate.

14. A sensor device according to any previous claim in which the analyte detection means comprises analyte sensing means.

15. A device according to claim 14 comprising a biosensor or chemical sensor.

16. A sensor device according to claim 14 or claim 15 in which the analyte sensing means comprises electrodes.

17. A sensor device according to any of claims 1 to 13 in which the analyte detection means comprises one or more reagents which participate in a reaction with an analyte thereby allowing identification of the analyte.

18. A method of preparing an analytical device according to any of claims 1 to 17 for use comprising the step of:

peeling the protective film from the substrate so as to either partially or wholly remove the film from the substrate thereby exposing at least a portion of the analyte detection means.

19. A method of packaging an analytical device comprising the steps of:

providing an analytical device comprising a substrate and analyte detection means disposed on said substrate;

heating sealing a protective film onto said substrate so that i) the protective film is disposed over at least a portion of the analyte detection means and ii) the protective film is partially or wholly removable from the substrate by peeling.

20. A method according to claim 19 in which the protective film is a flexible film.

21. A method according to claim 19 or claim 20 in which the heat sealing of the protective film permits partial or whole removal of the protective film from the substrate with a peel force of less than 50 N, preferably less than 10 N.

22. A method according to any of claims 19 to 21 in which the protective film is heat sealed along a continuous boundary so as to completely enclose a portion of the substrate.

23. A method according to claim 22 in which the protective film is hermetically sealed to the substrate.

24. A method according to any of claims 19 to 23 in which the substrate comprises a strip.

25. A method according to any of claims 19 to 24 further comprising the step of permanently attaching a portion of the protective film to the substrate.

26. A method according to any of claims 19 to 25 in which the device is a sensor device and the analyte detection means comprises analyte sensing means.

27. A method according to claim 26 in which the sensor device is a biosensor or chemical sensor.

28. A method according to claim 26 or claim 27 in which the analyte sensing means of the sensor device comprises electrodes.

29. A method according to any of claims 19 to 26 in which the analyte detection means of the device comprises one or more reagents which participate in a reaction with an analyte thereby allowing identification of the analyte.