An electrochemical test device for use in determining a concentration of each of a first analyte and a second analyte in a fluid sample is provided. The electrochemical test device comprises a set of electrodes including a first working electrode having sensing chemistry for the first analyte and a second working electrode having sensing chemistry for the second analyte, wherein the first analyte is lactate and the sensing chemistry for the lactate comprises lactate oxidase and an electron transfer agent, and wherein the sensing chemistry for the second analyte comprises a diaphorase, an electron transfer agent, an NAD(P).sup.+-dependent dehydrogenase and a cofactor for the NAD(P).sup.+-dependent dehydrogenase.

The present invention provides: a reagent composition having higher storage stability; a sensor involving the reagent composition; and others. According to the present invention, a specific heterocyclic compound is added to a reagent composition to improve the storage stability of the reagent composition and reduce the degree of fluctuation in current values in a sensor that utilizes reagent composition.

A reagent for detecting an analyte comprises a flavoprotein enzyme, a mediator such as a phenothiazine mediator, at least one surfactant, a polymer and a buffer. The reagent may be used with an electrochemical test sensor that includes a plurality of electrodes.

A non-leaching mediator may include a polymer having a polymeric backbone, and a plurality of phenothiazine groups bonded to the polymeric backbone. The plurality of phenothiazine groups may include at least one of a phenothiazine group having the general formula (IV):

##STR00001##

and salts thereof, where n is about 9 and R represents the polymeric backbone to which the phenothiazine group is bonded, and a phenothiazine group having the general formula (V):

##STR00002##

and salts thereof, where n is about 9 and R represents the polymeric backbone to which the phenothiazine group is bonded.

The present invention provides members that produce on a large scale a coenzyme-linked glucose dehydrogenase which has excellent substrate-recognizing ability toward glucose while providing low action on maltose. The present invention relates to a polynucleotide encoding a soluble coenzyme-linked glucose dehydrogenase that catalyzes the oxidation of glucose in the presence of an electron acceptor and has an activity toward maltose of 5% or lower; a polypeptide encoded by the nucleotide sequence of the polynucleotide; a recombinant vector carrying the polynucleotide; a transformed cell produced using the recombinant vector; a method for producing a polypeptide comprising culturing the transformed cell and collecting from the cultivated products a polypeptide that links to FAD to exert the glucose dehydration activity; a method for determination of glucose using the polypeptide; a reagent composition for determination of glucose; and a biosensor.

A reagent for detecting an analyte comprises a flavoprotein enzyme, a mediator such as a phenothiazine mediator, at least one surfactant, a polymer and a buffer. The reagent may be used with an electrochemical test sensor that includes a plurality of electrodes.

Disclosed is a biosensor with improved humidity resistance that can be used as a glucose sensor or a lactate sensor. The biosensor includes: an insulative substrate; an electrode system having a working electrode and a counter electrode provided on the substrate; and a reagent layer provided on the electrode system. The reagent layer contains an oxidoreductase and 1-methoxy-5-methylphenazinium ethyl sulfate. This biosensor can be used as a glucose sensor or a lactate sensor.

A method of determining the presence of bacteria expressing cytochrome c oxidase (the bacteria), the method comprising: providing a sample suspected of containing the bacteria; providing a compound that has two redox states: a reduced state and an oxidised state, wherein cytochrome c oxidase can convert the compound from its reduced state to its oxidised state; contacting an electrode either with (i) the compound in its oxidised state in the presence of the sample, then applying a reductive potential and measuring the current at the electrode; or (ii) the compound in its reduced state in the presence of the sample, then applying an oxidative potential and measuring the current at the electrode; and comparing the magnitude of the current produced by the reductive potential or oxidative potential in the presence of the sample suspected of containing the bacteria with the magnitude of the current produced under the same conditions, but in the absence of the sample suspected of containing the bacteria, wherein a difference between the magnitude of current produced in the presence of the sample suspected of containing the bacteria and the magnitude of current produced in the absence of the sample suspected of containing the bacteria indicates the presence of the bacteria. Also provided herein is a sensor for determining the presence of bacteria expressing cytochrome c oxidase.

A system for the electrochemical detection of ketone levels includes a test strip including an electrode and a counter electrode, the electrode and counter electrode located in a sample reception area. The system further includes a coating on one of the electrode and counter electrode, the coating including a mediator for ketones. Optionally, the mediator is ferricyanide.

The present invention provides members that produce on a large scale a coenzyme-linked glucose dehydrogenase which has excellent substrate-recognizing ability toward glucose while providing low action on maltose. The present invention relates to a polynucleotide encoding a soluble coenzyme-linked glucose dehydrogenase that catalyzes the oxidation of glucose in the presence of an electron acceptor and has an activity toward maltose of 5% or lower; a polypeptide encoded by the nucleotide sequence of the polynucleotide; a recombinant vector carrying the polynucleotide; a transformed cell produced using the recombinant vector; a method for producing a polypeptide comprising culturing the transformed cell and collecting from the cultivated products a polypeptide that links to FAD to exert the glucose dehydration activity; a method for determination of glucose using the polypeptide; a reagent composition for determination of glucose; and a biosensor.