Determination of blood glucose concentrations and corresponding medication are an essential part of the daily routine of diabetics. The blood glucose concentration has to be determined quickly and simply several times a day (typically two to seven times) in order, if appropriate, to be able to take suitable medical measures. In many cases, medication is administered by means of automated systems, in particular by what are called insulin pumps.
So as not to restrict the diabetic's daily routine any more than is necessary, suitable portable devices are often employed which are intended to be easy to carry around and to operate, such that the blood glucose concentration can easily be measured, for example, at the workplace or even during leisure time. Various portable devices are presently available on the market, some of them functioning with different measurement techniques and using different diagnostic techniques. A first measurement method is based, for example, on an electrochemical measurement technique, in which a blood sample is applied to an electrode coated with enzymes and mediators. Corresponding test strips for electrochemical measurement methods of this kind are described in U.S. Pat. No. 5,286,362, for example. Other known measurement techniques use optical measurement methods which, for example, are based on the fact that the substance to be detected can react with specific detection reagents, such that there is a change in the color of the reaction mixture. Systems for detecting color reactions of this kind, and therefore for detecting the corresponding analytes, are known from CA 2,050,677, for example.
It has been found that, because of the generally increasing incidence of disease with age, diabetes frequently occurs in elderly people. In elderly people, however, visual acuity is often impaired, particularly in poor lighting. Moreover, damage to the eyes is a common sequela of diabetes mellitus. For this reason, diabetics in particular require easy-to-read display elements in the portable measurement appliances used for self-monitoring. Similar problems also arise in other types of diseases for which portable appliances are used in the context of a homecare concept.
However, the portable medical systems presently available on the market, in particular portable glucose meters, typically use liquid-crystal displays (LCDs) as display instruments for glucose measurement values, warnings, messages, dates, times, etc. Segmented LCDs and also so-called matrix LCDs are used. Because of their low costs and easier control, segmented LCDs are predominantly used. Matrix LCDs are contained in a small number of glucose meters, these meters often being high-quality meters with extensive data management functions.
However, liquid-crystal displays have a number of disadvantages as far as their readability is concerned. In particular, liquid-crystal displays are not self-lighting. Instead, the liquid-crystal elements act only as “switches” for switching local transparency on and off. The symbols presented are thus made visible by means of transmitted light being blocked or let through at certain points of the display or in certain areas of the display. The light has to be provided, however, by means other that the liquid-crystal display itself. On the one hand, this can be done by ambient light being reflected on a reflecting surface behind the liquid-crystal display and being transmitted through the liquid-crystal display. In this case, however, the readability of the liquid-crystal display is strongly dependent on the illuminating strength of the ambient light. In dark surroundings, or in surroundings with poor lighting, liquid-crystal displays can be read only with difficulty or cannot be read at all.
This dependency of the liquid-crystal displays on ambient light can be reduced if light is transmitted through the liquid-crystal displays from behind or from the side (for example by means of light-emitting films or light-emitting diodes) (backlight display). However, a disadvantage of this technique is that the contrast of the display is impaired under good lighting conditions. This contrast cannot be optimized simultaneously for a presentation with and without backlighting, for which reason use of backlighting always leads to a compromise in the contrast of the display element. In addition, backlighting uses up quite a large amount of electrical energy, which can lead to a reduced useful life of the batteries in the meter. This reduced useful life is especially disadvantageous in portable meters in particular, for example portable glucose meters.
A further disadvantage of using liquid-crystal displays is that the readability of the liquid-crystal display is greatly dependent on the reading angle (typically defined as the angle between a normal to the display element and the viewing direction of an observer). This effect occurs both with and without additional backlighting. This greatly restricts the freedom of use of the glucose meter by the diabetic patient. This is particularly disadvantageous in view of the fact that many diabetics use the glucose meter by placing it on a table top in order to carry out a measurement. In some situations, this can involve reading angles at which the display is made difficult or even impossible to read.
In addition to liquid-crystal displays, a number of other display techniques are known. Thus, the technique of organic light-emitting diodes (OLEDs), which is used in various technical modifications, is known from other areas of technology. In organic light-emitting diodes, thin organic layers (one or more organic layers with a total thickness of typically between 50 and 300 nm) are embedded between two electrodes. If an electrical current is passed through the organic layers, a recombination of “electrons” and “holes” (or their organic pendants) takes place in the organic layers, in a manner similar to inorganic semiconductors. Photons are emitted in this recombination. This effect is referred to as organic electroluminescence.
Organic light-emitting diodes are normally constructed as thin-layer systems on a transparent substrate, for example a glass or plastic substrate. Electrode layers and organic layers are usually built up in succession, until the above-described sandwich structure is obtained. A transparent electrode layer, for example indium tin oxide, is normally used as the first electrode layer (for example anode layer). A metal layer, for example calcium or magnesium, is used for example as counterelectrode (usually cathode). The sandwich structure is then suitably encapsulated, in order to protect the structure against the influence of air humidity and oxygen. In addition to this standard structure as described, other structures are also known, for example structures with several OLEDs stacked on one another, or structures in which light is emitted not through the glass substrate, but through a transparent metal electrode layer. Furthermore, there are also various techniques that differ in terms of the organic materials used. Thus, there are techniques in which the materials are composed of (generally vapor-deposited) monomolecular substances. Other techniques use polymers, generally applied by wet chemistry, as organic materials. Hybrid techniques are also known to persons skilled in the art.
Organic light-emitting diodes are now used as lighting means or otherwise for lighting purposes in various technological fields. Examples are cell phones, mixing desks in the audio sector, digital camera displays, and MP3 players or multimedia players. Examples of use are also found in the medical field. In addition to their use as lighting means, applications of OLEDs as display elements are also known in medicine. The medical systems known from the prior art and using OLED displays are typically stationary systems of considerable size, which cannot easily be carried around by a patient on his or her body. Exemplary disclosures of OLEDs for these various purposes and various fields include WO 2004/048881 A2, US 2003/0035109 A1, US 2005/0015115 A1, U.S. Pat. No. 6,579,237 B1, DE 102 53 154 A1, and US 2003/0004403 A1, the disclosures of each of which are hereby incorporated herein by reference in their respective entireties.
It is further known from the prior art to provide a measuring device for determination of an analyte in a liquid sample, comprising a test element with a test field and a detector, in which electrical components are used that are based at least partially on polymer electronics. However, the disadvantage of such measurement devices based on polymer electronics is that polymer electronics, in particular transistors on an organic basis, according to the prior art are still rather susceptible to failure and permit only designs with comparatively low electronic functionality.
A problem in using OLED displays, which is known from other technical fields, is that the displays used often have quite a short useful life and tend to be highly susceptible to errors. This is due in particular to the fact that the organic materials used degrade with time. Furthermore, quality control often proves difficult, and, for example, the electrode materials used (for example reactive metals such as calcium or magnesium) tend to cause oxidization effects. These effects have the result that individual pixels, individual rows or columns, and in some cases entire displays, fail slowly or unexpectedly suddenly. Devices using such displays are generally unable to detect and react to such minimal effects of the kind that arise, for example, through failure of individual rows or columns.
However, specifically in the case of medical appliances, in particular medical appliances used privately for self-monitoring and/or for self-medication, such a failure is often associated with fatal consequences. It can happen, for example, that elderly patients in particular do not notice that faults have occurred or, even if the faults are in fact noticed, they do not react to these faults as they should. This can lead, for example, to incorrect medication, with well-known serious consequences. In this context, so-called segmented displays, for example 7-segment displays, have proven disadvantageous in particular, because in this case the unobserved failure of individual segments can easily lead to distortion of the values displayed. For example, the display “7” can easily result in the display “1” if the top horizontal stroke is missing. In the medical field, a defect of this kind in displays can have fatal consequences.
It is therefore an object of the present invention to make available a portable medical system which is extremely user-friendly in respect of the display properties described above and which is extremely reliable, while at the same time substantially or completely avoiding the described disadvantages of the prior art. Any faults that occur are intended to be identified as quickly as possible, so as to allow appropriate measures to be taken.