Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Sample mechanical transport means in or for automated...
Reexamination Certificate
1996-03-15
2001-02-13
Alexander, Lyle A. (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Sample mechanical transport means in or for automated...
C422S051000, C436S165000, C436S169000
Reexamination Certificate
active
06187269
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to assay devices. More particularly it relates to ways in which sensitive reagents within such devices may be protected against moisture-induced degradation during storage.
BACKGROUND TO THE INVENTION
Many assay devices are now available commercially which are intended for quick simple tests in professional circumstances (clinics and doctor's offices) or in the home (for example pregnancy tests). Typically such assays are based on specific binding reactions, and therefore use sensitive reagents such as antibodies. A typical test device will comprise a strip of porous material within a plastics casing. The reagents are contained within the device in the dry state, and when sample liquid (such as urine) is applied to the device it migrates through the porous material and initiates one or more specific binding reactions which lead to the test result. Examples of such devices are described in EP-A-291194 the disclosures of which are included herein by reference.
These assay devices are manufactured and distributed on a large scale, and need to have a lengthy shelf life. The user expects the assay to be highly sensitive and therefore any deterioration in the performance of the assay reagents during storage would be unacceptable. To this end it is common practice for such devices to be provided in individual moisture-impervious packaging such as an aluminium foil pouch. A desiccant is provided within the pouch together with the assay device. Conventionally this is in the form of a small sachet of silica gel. As an alternative, a compressed tablet of desiccant (usually molecular sieve material) can be incorporated within the device itself. Both of these approaches have significant disadvantages.
The necessity to include a sachet of desiccant inside each foil pouch complicates the packaging process. More important, the sachet of desiccant is of no value to the consumer and must be discarded with the rest of the packaging. It can easily become separated from the remainder of the packaging. If mislaid in the home it may be found by an inquisitive child and perhaps ingested with potentially disastrous consequences.
The inclusion of a tablet of desiccant within the device itself adds a further step to the assembly process, and necessitates moulding features to accommodate and retain the tablet. In terms of storage stability there does not appear to be any extra benefit associated with having an internal tablet of desiccant compared to the effectiveness of an external sachet.
GENERAL DESCRIPTION OF THE INVENTION
By the invention we have found that all of these disadvantages can be overcome by incorporating desiccant within the material structure of one or more plastics mouldings from which the device is assembled.
The invention provides an assay device comprising a casing enclosing one or more reagents which are susceptible to moisture-induced degradation during storage, wherein the casing is constructed at least in part of desiccant-containing plastics material. Preferably the desiccant-containing plastics material is enrobed or shielded within non-desiccant-containing plastics material; this can be achieved, for example by sandwich injection moulding.
Conveniently, the desiccant-containing plastics material forms at least part of a removable cap or shroud which forms part of the device as supplied to the user; for example, the cap or shroud can protect means whereby sample liquid can be received into the remainder of the device.
A preferred embodiment of the invention is an assay device comprising within a casing an assay strip together with at least one reagent in the dry state which can participate in a specific binding reaction to reveal the assay result following application of a sample liquid to the device, the casing having means whereby the sample liquid can be applied directly or indirectly to the strip, and wherein a removable cap or shroud is provided to protect the sample liquid application means, the cap or shroud incorporating desiccant in an amount sufficient to enhance storage stability of the reagent. Preferably the cap or shroud is moulded of desiccant-containing plastics material.
Preferably the desiccant-containing plastics material comprises a blend of polystyrene and silica gel. This can be enrobed within conventional plastics material, such as polystyrene. Hence the cap or shroud is preferably manufactured by a process involving sandwich injection moulding.
Very suitable desiccant-containing plastics materials are described in EP-A-599690 the disclosures of which are incorporated herein by reference. A typical desiccant-containing plastics material will comprise, by weight, about 60-65% of thermoplastic or thermosetting polymer such as polystyrene and about 30% of powdered desiccant such as silica gel dust and/or molecular sieve dust. The properties of this blend can be improved by incorporating a few percent of elastomer, and minor amounts of fibrous material. Despite the presence of the desiccant, the blended material can be moulded and processed using the techniques commonly employed in the plastics moulding industry.
According to EP-A-599 690, an ideal desiccant-containing plastics material comprises a blend of:
any thermoplastic or thermosetting polymer, especially polystyrenes, polyolefins (polyethylene, polypropylene), polyamides, polyvinyl chloride alone or combined, or unsaturated polyesters, phenolic resins, bakelites and polyurethanes, alone or combined;
a desiccant such as silica gel and molecular sieves;
an elastomer, such as styrene-butadiene rubbers (SBR), styrene-ethylene-butadiene-styrene copolymers (SEBS), butyl rubbers, ethylene-propylene rubbers (EPR), ethylene-propylene-diene rubbers (EPDM), copolymers of ethylene-vinyl acetate (EVA), ethylene-acrylate or acrylonitrile-butadiene, polynorbornenes, polyisoprenes, polychloroprenes or polybutadienes;
and fibres of length between 0.5 and 4 mm, for example acrylic, polyester or polyamide fibres or natural fibres of animal origin such as wool or silk or of vegetable origin such as cotton or linen.
Optionally, the dessicant-containing plastics material may optionally also contain any conventional inorganic or organic additives, in particular plasticisers, stabilisers, dyes and pigments.
If desired, the desiccant-containing plastics material can be used to form any part of, or indeed the whole of, the plastics mouldings from which the assay device is prepared. However we have found that an ideal circumstance in which to use the desiccant-containing plastics material is in the manufacture of a separate cap or shroud associated with the assay device.
The assay device must have some means whereby sample liquid is applied to the device to initiate the assay. In some devices this is an orifice in the moulding, into which sample liquid can be added eg. dropwise using a pipette. In other devices the sample application is achieved by direct contact of the device with a sample source such as a urine stream. To facilitate sample collection in this latter situation, the device is sometimes provided with a protruding porous member which can take up sample liquid and transfer it elsewhere within the device. In all of these formats it is useful to have a removable cap or cover which can protect the site of sample addition.
There are a number of advantages associated with including the desiccant in the cap as distinct from any other part of the device moulding. The cap will usually be a relatively simple structure, whereas the main device mouldings may be of complex shape necessary to locate and retain specific physical components within the device. Difficulties may arise in attempting to mould a complex high-precision structure from the desiccant-containing plastics material. Moulding difficulties are much less likely to arise in the manufacture of the structurally simpler cap.
The cap will be a comparatively small part of the entire device, so less desiccant-containing plastics material will be required in the moulding. This may be important from cost considerations
Lancesseur Didier
Wiles Stewart John
Alexander Lyle A.
Pillsbury Madison & Sutro LLP
Unipath Limited
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