For the diagnosis and prophylaxis of diabetes mellitus, the importance of periodically monitoring blood glucose levels is increasingly emphasized. Nowadays, strip-type biosensors designed to be used in hand-held reading devices allow individuals to readily monitor glucose levels in blood.
A large number of commercialized biosensors measure the blood glucose content of blood samples using an electrochemical technique. The principle of the electrochemical technique is based on the following Reaction 1.Glucose+GOx-FAD→gluconic acid+GOx-FADH2 GOx-FADH2+Mox→GOx-FAD+Mred  [Reaction 1]
wherein, GOx represents glucose oxidase; GOx-FAD and GOx-FADH2 respectively represent an oxidized and a reduced state of glucose-associated FAD (flavin adenine dinucleotide), a cofactor required for the catalysis of glucose oxidase; and Mox and Mred denote the oxidized and reduced states of an electron transfer mediator, respectively.
The electrochemical biosensor uses as electron transfer mediators organic electron transfer materials, such as ferrocenes or their derivatives, quinines or their derivatives, organic or inorganic materials containing transition metals (hexaamine ruthenium, polymers containing osmium, potassium ferricyanide and the like), organic conducting salts, and viologens.
The principle of measuring blood glucose using the biosensor is as follows.
Glucose in the blood is oxidized to gluconic acid by the catalysis of the glucose oxidase, with the cofactor FAD reduced to FADH2. Then, the reduced cofactor FADH2 transfers electrons to the mediator, so that FADH2 returns to its oxidized state; that is, FAD and the mediator are reduced. The reduced mediator is diffused to the surface of the electrodes. The series of reaction cycles is driven by the anodic potential applied at the working electrode, and redox current proportional to the level of glucose is measured. Compared to biosensors based on colorimetry, electrochemical biosensors (that is, based on electrochemistry) have the advantages of not being influenced by the turbidity or color of the samples and allowing the use of wider range of samples, even cloudy ones, without pretreatment thereof.
Although this electrochemical biosensor is generally convenient when used to monitor and control the amount of blood glucose, its accuracy is greatly dependent on the lot-to-lot variation between respective mass-production in which the biosensors are produced. In order to eliminate such variation, most of the commercialized biosensors are designed such that a user directly inputs calibration curve information, which is predetermined at the factory, into a measuring device capable of reading the biosensor. However, this method inconveniences the user a great deal and causes the user to make input errors, thus leading to inaccurate results.
In order to solve this problem, a method by which the resistance of each electrode can be adjusted such that the variations in mass production is corrected (US20060144704A1), a method in which a conductor is printed in a bar code fashion on the biosensor strip to record the production information (U.S. Pat. No. 6,814,844), a method in which a connection to a resistor bank is made (WO2007011569A2), and a method by which information is read by varying resistance through the adjustment of the length or thickness of each electrode (US20050279647A1) have been proposed. The methods proposed for the electrochemical biosensors are all based on a technique in which electrical variation is read. Furthermore, a method for distinguishing production lot information by reading the resistivity of a conductor marked on a strip using an electrical method (U.S. Pat. No. 4,714,874) has been proposed.
However, these methods function to accurately adjust resistance, and require a process of mass-producing the sensors first, measuring the statistical characteristics of the sensors, and post-processing the measured information again using a method of adjusting the resistance marked on the sensors. However, the process of accurately adjusting the resistance, marked in large quantities, through the post-processing is very inconvenient, and is difficult to use in practical applications.
Methods in which colored marks are used with a spectral system capable of discriminating colors to realize a colorimetric method (U.S. Pat. No. 3,907,503, U.S. Pat. No. 5,597,532, U.S. Pat. No. 6,168,957), a method in which a plurality of color marks is read at various wavelengths of visible and infrared ray regions using a spectroscope (U.S. Pat. No. 5,945,341), and a method capable of reading bar codes (EP00075223B1, WO02088739A1) have been proposed. These methods using color or bar codes are favorable for a colorimetric method-based sensor using the spectrum system, but they have technical and economic difficulties when applied to a system using an electrochemical measurement mechanism. For example, the size and structure of a portion where the electrochemical sensor strip is inserted into the measuring device for the purpose of electrical connection, that is, a connection space of the sensor strip, is very limited in constructing a device and circuit for spectroscopically identifying a structure into which the production lot information is input. Further, as shown in FIG. 1, because a light emitter-detector system is operated in a manner such that the detector senses the light reflected by or transmitted through a production lot information identification portion to which light is projected from photodiodes of various colors, a process of scattering various wavelengths of the detected light using a filter is required to identify the information of the light, which makes the calculation process, the device, and the program complicated. Thus, the expense for constructing the system is greatly increased.
Furthermore, instead of the methods of marking the production lot information on the sensor strip, a method of recording information on a container or pack containing a sensor and allowing the information to be read by the measuring device (EP0880407B1) has been proposed. However, this method also has a possibility of causing the user to make an error in which a code recorded on the container is incorrectly read.
Leading to the present invention, intensive and thorough research into electrochemical biosensors, conducted by the present inventors, aiming to maintain economic efficiency in the construction of the measuring device while allowing the mass production of an electrochemical biosensor in which the production lot information thereof can be easily and accurately input into the measuring device and which removes the risk of mistakes being made by the user, thus providing an accurate measurement value, resulted in the finding that, when the production lot information is recorded on the electrochemical biosensor strip using infrared absorption/reflection marks and when a production lot information identification portion, at which the production lot information is recorded on the electrochemical biosensor strip, is identified in the measuring device, there is no need to use a high-priced filter in the case where photodiodes of various colors sequentially emit light at regular time intervals, so that the light emitter-detector system has a simple construction and is formed on the same printed circuit board (PCB) of measuring device, and thus can not only reduce a complicated calculation process performed for post-treatment but also maintain economic efficiency in the construction of the measuring device.