Chemical apparatus and process disinfecting – deodorizing – preser – Control element responsive to a sensed operating condition
Reexamination Certificate
2000-09-21
2004-02-24
Alexander, Lyle A. (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Control element responsive to a sensed operating condition
C422S051000, C436S180000, C436S170000
Reexamination Certificate
active
06696024
ABSTRACT:
The invention concerns a device for the capillary transport of a liquid between two opposite, essentially planar layers, in which the two layers are arranged parallel to one another at such a distance that there is a capillary-active gap between the two layers.
So-called carrier-bound tests are often used for the qualitative or quantitative analytical determination of components of body fluids, in particular of blood. In these the reagents are embedded in corresponding layers of a solid carrier which is contacted with the sample. If a target analyte is present, the reaction of the liquid sample and reagents leads to a detectable signal, in particular a colour change which can be evaluated visually or with the aid of an instrument, usually by reflection photometry.
Test elements or test carriers are often in the form of test strips which are essentially composed of an elongate support layer made of plastic material and detection layers which are applied thereto as test fields. However, test carriers are also known which are in the shape of small quadratic or rectangular plates.
Test elements for clinical diagnostics that are evaluated visually or by reflection photometry are frequently constructed, like electrochemical sensors and biosensors, such that the sample application zone and the detection zone are arranged one above the other in a vertical axis. This mode of construction is problematic. When the test strip loaded with sample has to be inserted into an instrument, for example a reflection photometer, for measurement, potentially infectious sample material can come into contact with parts of the instrument and may contaminate them. Furthermore volumetric dosing can only be achieved with difficulty especially in cases in which the test strips are used by untrained persons for example in the self-control of blood sugar by diabetics.
Test elements have recently become available which provide a capillary channel or gap which solves at least some of the described problems.
EP-A-0 287 883 describes a test element which utilizes a capillary interspace between the detection layer and an inert carrier for volumetric dosing. The test element is dipped into the sample to be examined to fill the capillary space requiring large sample volumes which is why this type of volumetric dosing is primarily suitable for the examination of sample material that is present in excess such as urine. There is no spatial separation between the site of sample application and the site of detection.
EP-B-0 034 049 concerns a test element in which the sample is applied to a central sample application site for example an opening in a cover and is transported by capillary force to several detection zones which are spatially separated from the sample application site. The central position of the sample application site in a test element according to EP-B-0 034 049 does not solve the problem of instrument hygiene as described above.
In the described capillary gap test elements, the capillary gap is in each case formed by continuous one-part layers. It would be desirable that at least one layer would be composed of several adjacent parts made of different materials especially in cases where the capillary transport is over not inconsiderable distances such as more than 10 mm, especially to deal with the problem of instrument hygiene. The different materials could then be used for zones with different tasks such as for transport zones, reservoir zones and/or reaction zones. The use of different materials would then enable a specific optimization of the material properties with regard to their desired purpose. However, this poses the problem that even very slight changes in the dimensions of the gap or channel responsible for the capillary effect lead to an abrupt termination of the capillarity. Increases in the cross-section in a micrometer range are adequate for this. Maintenance of capillary continuity at the junction of different zones is a problem which to the knowledge of the applicant has up to now not been satisfactorily solved.
The object of the present invention was therefore to eliminate the disadvantages of the prior art.
This is achieved by the subject matter of the invention as characterized in the patent claims.
The invention concerns a device for the capillary transport of a liquid between two opposite essentially planar layers, in which the layers are arranged at a distance parallel to one another so that there is a capillary-active gap between the two layers, which is characterized in that at least one of the two layers contains at least two discrete adjacent parts and that the capillary-active transport of the liquid is possible beyond the common boundary of the parts that lie in one layer. The opposite planar layers are preferably provided with hydrophilic properties.
In this connection hydrophilic surfaces are water-attracting surfaces. Aqueous samples, also including blood, spread well on such surfaces. Such surfaces are characterized among others in that a water drop placed on it forms an acute rim angle or contact angle at the interface. In contrast an obtuse rim angle is formed at the interface between a water drop and surface on hydrophobic i.e. water repellent surfaces.
The rim angle which is a result of the surface tensions of the test liquid and of the surface to be examined is a measure of the hydrophilicity of a surface. Water for example has a surface tension of 72 mN/m. If the value of the surface tension of the observed surface is much below this value i.e. more than 20 mN/m below this value, then the wetting is poor and the resulting rim angle is obtuse. Such a surface is referred to as hydrophobic. If the surface tension approximates the value which is found for water then the wetting is good and the rim angle is acute. If, in contrast, the surface tension is the same as or higher than that of the value found for water, then the drop runs and there is a total spreading of the liquid. It is then no longer possible to measure a rim angle. Surfaces which form an acute rim angle with water drops or on which a total spreading of a water drop is observed are referred to as hydrophilic.
The ability of a capillary to aspirate a liquid depends on the wettability of the channel surface with the liquid. This means for aqueous samples that a capillary should be manufactured from a material whose surface tension almost reaches 72 mN/m or exceeds this value.
Sufficiently hydrophilic materials for the construction of a capillary which rapidly aspirates aqueous samples are for example glass, metal or ceramics. However, these materials are unsuitable for use in test carriers since they have some severe disadvantages such as risk of breaking in the case of glass or ceramics or change in the surface properties with time in the case of numerous metals. Therefore plastic foils or moulded parts are usually used to manufacture test elements. As a rule the plastics used hardly exceed a surface tension of 45 mN/m. Even with the, in a relative sense, most hydrophilic plastics such as polymethylmethacrylate (PMMA) or polyamide (PA) it is only possible—if at all—to construct slowly sucking capillaries. Capillaries made of hydrophobic plastics such as for example polystyrene (PS), polypropylene (PP) or polyethylene (PE) essentially do not suck aqueous samples. Consequently it is necessary to endow the plastics used as a construction material for test elements with capillary active channels with hydrophilic properties i.e. to hydrophilize them.
In a preferred embodiment of the analytical test element according to the invention at least one, but preferably two and especially preferably two opposite surfaces which form the inner surface of the channel capable of capillary liquid transport are hydrophilized. If more than one surface is hydrophilized then the surfaces can either be made hydrophilic using the same or different methods. Hydrophilization is particularly necessary when the materials that form the capillary active channel, in particular the carrier, are themselves hydrophobic or only very slightl
Leichner Wilhelm
Schwobel Wolfgang
Zimmer Volker
Alexander Lyle A.
Roche Diagnostics GmbH
Woodburn Jill L.
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