A highly sensitive biosensor that uses a smaller amount of sample for measurement is described. The biosensor includes a first insulating base plate having a working electrode, a second insulating base plate having a counter electrode opposed to the working electrode, and a reagent layer containing at least an oxidoreductase. The biosensor further includes a sample supply pathway formed between the first and second insulating base plates, where the working electrode, counter electrode and reagent layer are exposed to an inside of the sample supply pathway, and the distance between the working electrode and the counter electrode is 150 μm or less.
1. A biosensor comprising a first insulating base plate having a working electrode, a second insulating base plate having a counter electrode opposed to said working electrode, a reagent layer comprising at least an oxidoreductase, and a sample supply pathway formed between the first and second insulating base plates, wherein said working electrode, counter electrode and reagent layer are exposed to an inside of said sample supply pathway, and the distance between said working electrode and said counter electrode is 150 μm or less, and the area of said counter electrode exposed to the sample supply pathway is smaller than the area of said working electrode exposed to the sample supply pathway.
2. The biosensor in accordance with claim 1 , wherein the area of said working electrode exposed to the sample supply pathway is 0.1 to 2.0 mm 2 , and the area of said counter electrode exposed to the sample supply pathway is in a range of not less than 0.05 mm 2 and less than 2.0 mm 2 .
3. The biosensor in accordance with claim 1 , wherein the distance between said working electrode and said counter electrode is 40 μm or more.
4. The biosensor in accordance with claim 1 , wherein a spacer member having a slit is interposed between the first and second insulating base plates such that said sample supply pathway is formed in said slit.
5. A biosensor comprising a first insulating base plate having a working electrode, a second insulating base plate having a counter electrode opposed to said working electrode, a reagent layer comprising at least an oxidoreductase, and a sample supply pathway formed between the first and second insulating base plates, wherein said working electrode, counter electrode and reagent layer are exposed to said sample supply pathway, and the area of said counter electrode exposed to the sample supply pathway is less than the area of said working electrode exposed to the sample supply pathway.
6. The biosensor in accordance with claim 5 , wherein the distance between said working electrode and said counter electrode is 150 μm or less.