Measurements of analytes in blood is commonly performed by sampling blood from patients and analyzing said samples in a laboratory, often situated at a location remote from the ward. E.g. for glucose analysis there are available special reagent sticks usable for measuring on site i.e. in the ward. However, the accuracy of such measurements is questionable, and the error could be 10-20% at best.
Often it is necessary to perform several sequential measurements over periods of several hours, which is very labor intensive. Furthermore, the risk for errors because of the human intervention is evident, and the low accuracy is of course also a drawback in this regard.
For the purposes of this application, the term “biosensor” means any device having a portion which interacts with biological or biochemical material, and has the capability to generate a signal indicative of a change in some parameter of said biological or biochemical material as a consequence of said interaction.
When analytes such as glucose, urea, lactate, ATP, glycerol, creatinine and pyruvate in biological samples, such as blood, plasma or serum are analyzed using biosensor techniques based on immobilization of enzymes, the sensor surface will be exposed to a certain amount of sample during a certain time sufficient to achieve an adequate sensor response. It is well known that the sensor response gradually will degrade because of fouling of the surface. This in its turn is a consequence of said exposure and the interaction between the surface and the substances present in the sample that occurs. The chemical and physical composition of the sample is thereby of importance, the sample i.a. comprising red cells, blood platelets, macromolecules, electrolytes, lipids, red/ox-compounds etc. It is also known that the support material for the enzyme immobilization in biosensors based on enzyme column technology is fouled by the substances present in the sample.
In cases where selective membranes are used for protection of the sensor surface of biosensors based on enzyme electrode technology, said membranes are also fouled by such substances.
This fouling influences the sensor response by substantially reducing the life and stability of the biosensor.