Among the conventional biosensors is a biosensor for measuring the density of glucose in blood, as disclosed in the Japanese Patent Publication No. 5-256811. The conventional sensor comprises, as shown in FIG. 3, leads 2 and 3 formed on an insulating substrate 1 by a screen-printing technology, and a measuring electrode 4 and a counter-electrode 5, coupled respectively with leads. On the measuring electrode 4 and the counter-electrode 5 is a reagent layer 6 comprised of glucose oxidase as an enzyme, potassium ferricyanide as a mediator, etc.
On the insulating substrate 1, a cover 10 having an air hole 9 is attached with a spacer 8 having a void 7 at one end in between. These components constitute a biosensor.
For measuring the blood glucose density using a conventional biosensor having the above described constitution, one end of a capillary formed by the void 7 of spacer 8 is placed on blood, then the blood is sucked into the capillary by a capillary phenomenon with the other end of the capillary forming an air hole 9, and the reagent layer 6 is resolved causing an oxidation/reduction. If a voltage is applied between measuring electrode 4 and counter-electrode 5, electric current flows in proportion to the density of glucose. The blood sugar level is thus measured.
In the conventional biosensor, carbon is employed as an electrode material suitable for the potassium ferricyanide mediator. The electrode is formed through screen-printing technology.
Namely, a silver paste is screen-printed on substrate 1 for forming the leads 2 and 3, and a carbon paste is screen-printed to form the measuring electrode 4 and the counter-electrode 5. Then, in order to regulate the effective area of measuring electrode 4, a resist layer is formed on the electrode and the leads by screen-printing an insulating paste.
In a conventional manufacturing method wherein a screen-printing process is employed a plurality of times, drying time is needed after each of the steps of paste preparation and screen-printing. The drying thus increases manufacturing time.
Furthermore, in printing the insulating paste, it is inevitable that some paste will ooze out as a result. A wide dispersion in the area of measuring electrode 4 and an adverse influence on the accuracy of response of the finished biosensor will result. Therefore, a need exists to develop a simpler method of providing an measuring electrode, while at the same time enabling a biosensor of higher measuring accuracy to be obtained.