Optics: measuring and testing – For light transmission or absorption – By comparison
Reexamination Certificate
2001-09-04
2004-03-16
Adams, Russell (Department: 2851)
Optics: measuring and testing
For light transmission or absorption
By comparison
C356S435000, C356S436000, C356S039000
Reexamination Certificate
active
06707554
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a method for the photometric analysis of test elements with detection zones, said method being stable in relation to positioning tolerances of the detection zone.
The photometric analysis of test elements is one of the most common methods for rapidly determining the concentration of analytes in samples. Photometric analyses are generally carried out in the field of analytics, environmental analytics and above all in the field of medical diagnostics. Test elements that are analysed photometrically play an important role especially in the field of blood glucose diagnostics from capillary blood.
The general trend in performing analytical tests is to reduce the amounts of sample. This is often due to the fact that only small amounts of sample are present. For example in the field of blood sugar determination, the diabetic himself removes a drop of blood from the finger pad and a reduction in the amount of blood required for the test considerably increases the convenience. This is primarily due to the fact that it is possible to select a smaller depth of cut for the blood collection. A reduction in the amounts of sample is linked to a miniaturization of the test elements and in particular of the detection zones in which the actual reaction of the sample with the analyte takes place. Hence in order to carry out an exact photometric analysis it is necessary to precisely position the detection zone. Numerous test element holders are known in the prior art which allow a quite accurate relative positioning of the detection zone and measurement optics. The European Patent EP-B-0 618 443 (corresponding to U.S. Pat. No. 5,424,035) is mentioned here as an example in which the detection zones of the test element are positioned laterally as well as vertically relative to the measurement optics. The document EP-A-0 319 922 is also mentioned as representative of many other analytical systems which carry out a positioning of test strips. However, the systems known in the prior art operate with detection zones which exceed 5 mm×5 mm. Consequently a positioning in the manner known in the prior art is relatively unproblematic. However, if the lateral dimensions of the detection zone are reduced, great efforts have to be made in the manufacture of the test elements as well as in the positioning within an analytical system in order to obtain reliable analytical results. The object of the present invention was to propose a method and a device of the photometric analysis of test elements which also allow the reliable analysis of test elements with small detection zones.
SUMMARY OF THE INVENTION
This object is achieved by a method for the photometric analysis of test elements in which the test element is placed in a holder in which its detection zone is positioned such that it is disposed relative to an illumination unit with at least two light sources. After the detection zone has been contacted with the sample to be analysed, a first light source is activated in order to irradiate the detection zone. Light reflected from the detection zone or transmitted through the detection zone is detected as a first detection signal. Afterwards a second light source is activated which irradiates a second area of the detection zone which is offset from the first area in the direction of the expected positioning tolerance. The light reflected from this area of transmitted through this area is detected as the second detection signal. The detection signals obtained from the two areas are compared and examined to determine which of the signals was obtained by illumination of an area situated completely in the detection zone. A corresponding detection signal is selected and analysed to determine the analyte concentration in a basically known manner.
A further subject matter of the present invention is a method which can rapidly detect whether an adequate amount of sample liquid has been added to the test element or the detection zone and reports this back to the operator.
In the field of analysis with test elements it is a considerable gain in convenience when the time required to apply sample liquid to a test element can be reduced and when there is also a feedback about whether the applied amount of sample is sufficient. In the case of test elements which utilize an electrochemical principle, it has been common practice for some time to indicate to the user when sample liquid has penetrated into the analytical zone so that he can stop adding sample. In the case of test elements based on electrochemistry this detection can be achieved in a simple manner by a conductivity measurement. However, in the field of optical measurement of test elements such a rapid application detection cannot easily be accomplished. Methods are for example described in the documents U.S. Pat. No. 4,109,261 and EP-A-0 256 806 in which a sample application is detected by the optical system which carries out the measurement and is used as a start signal for awaiting an incubation period. However, in these described methods the user receives no feedback about whether he has applied sufficient sample liquid and can stop further addition. Furthermore optical systems are used in the described methods which detect colour formation in the detection zone of the test element. As shown in
FIG. 7
of this application, several seconds pass between contacting the detection zone with sample liquid and the start of colour formation. If for example in the case of a blood sugar test the user has to hold his finger on the test element until a colour reaction is initiated this would be felt by him to be a constraint on his personal freedom. There is therefore a need to reduce the time for the addition or until the detection of the sample liquid. A blood sugar measuring instrument is described for example in EP-A-0 166 876 in which sample application is detected but it does not allow a check of whether the sample quantity is adequate.
Hence a method is proposed as part of the present invention which allows a rapid detection of sample application on a test element. The method according to the invention for the photometric analysis of test elements comprises the following steps:
irradiation of a control area of the detection zone,
transporting sample liquid to the detection zone in such a manner that a first zone of the detection zone comes in contact with the sample liquid earlier than a second zone which is at a lateral distance from the first zone
monitoring the radiation reflected from the control area or transmitted through the control area,
detecting presence of sample liquid in the control area as a result of a change of the reflected or transmitted radiation
irradiating a detection area of the detection zone
detecting irradiation which has been reflected from the detection area or transmitted through the detection area
analysing the detected radiation in order to determine the concentration of an analyte in the sample liquid,
characterized in that
when the presence of sample liquid is detected in the control area, a signal is emitted so that the supply of sample liquid can be terminated.
In the following the method according to the invention for compensating positioning tolerances is described first.
A device with which the method according to the invention can be carried out has a holder in which a test element is positioned relative to an illumination unit which is also part of the device. Holders that are known in the prior art and especially the holder described in EP-B-0 618 443 can be used in the following invention. Despite the inventive procedure which stabilizes the analysis in relation to positioning tolerances, it is desirable that the holder already results in a positioning of the detection zone that is as accurate as possible. However, the positioning tolerances cannot be reduced below a certain threshold which becomes clearer when one considers the individual factors that impact on the positioning tolerances. The analytical system already results in a number of tolerances for a relative
Miltner Karl
Ruppender Uwe
Wersig Christian
Zimmer Volker
Adams Russell
Brinks Hofer Gilson & Lione
Roche Diagnostics GmbH
Sever Andrew
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