Small volume in vitro analyte sensor and methods of making
A sensor utilizing a non-leachable or diffusible redox mediator is described. The sensor includes a sample chamber to hold a sample in electrolytic contact with a working electrode, and in at least some instances, the sensor also contains a non-leachable or a diffusible second electron transfer agent. The sensor and/or the methods used produce a sensor signal in response to the analyte that can be distinguished from a background signal caused by the mediator. The invention can be used to determine the concentration of a biomolecule, such as glucose or lactate, in a biological fluid, such as blood or serum, using techniques such as coulometry, amperometry; and potentiometry. An enzyme capable of catalyzing the electrooxidation or electroreduction of the biomolecule is typically provided as a second electron transfer agent.
1. A system comprising:
a biosensor comprising a first electrode, a second electrode, a third electrode, and a reagent layer including a reagent which reacts specifically with glucose in a sample solution, which biosensor measures the concentration of the glucose in the sample solution, said reagent layer being present in a sample chamber of the sensor and including glucose dehydrogenase having a coenzyme; and
a sensor reader configured to:
apply a first potential between the first and second electrodes to determine when the sample chamber is beginning to fill with sample;
apply a second potential between the first and third electrodes to determine with the sample chamber is substantially filled with sample;
apply a third potential between the first and second electrodes to electrolyze the glucose, thereby generating a glucose signal; and
measure the concentration of the glucose using the glucose signal.
2. A system as defined in claim 1 , wherein the concentration of the glucose in the sample solution is measured using electrodes including at least a working electrode and a counter electrode, which electrodes are disposed in the sample chamber.
3. A system as defined in claim 2 , wherein the reagent layer, including an electron carrier, is formed on the working electrode.
4. A system as defined in claim 2 , wherein the working electrode and counter electrode are disposed in a facing configuration.
5. A system as defined in claim 2 , wherein the working electrode and counter electrode are disposed in a coplanar configuration.
6. A system as defined in claim 2 , wherein the working electrode and the counter electrode are separated by a closest distance that is no more than 100 μm.
7. A system as defined in claim 2 , wherein the working electrode and the counter electrode are separated by a closest distance that is no more than 50 gm.
8. A system as defined in claim 2 , wherein the biosensor comprises an indicator electrode disposed in the sample chamber.
9. A system as defined in claim 8 , wherein the working electrode, counter electrode, and indicator electrode are disposed in a coplanar configuration.
10. A system as defined in claim 1 , wherein the reagent layer, including an electron carrier, is formed so that the electrodes are disposed in a diffusion area wherein the reagent of the reagent layer is dissolved in the sample solution and diffused.
11. A system as defined in claim 1 , wherein the biosensor comprises an electron carrier comprising:
a transition metal selected from the group consisting of osmium, ruthenium, iron, and cobalt;
two or more ligands coordinately bound to the transition metal, wherein at least one of the ligands is a heterocyclic nitrogen-containing bidentate ligand comprising
wherein R 1 is selected from hydrogen, hydroxy, alkyl, alkoxy, alkenyl, vinyl, allyl, amido, amino, vinylketone, keto, or sulfur-containing groups.
12. A system as defined in claim 11 , wherein the transition metal is osmium.
13. A system as defined in claim 11 , wherein R 1 is an alkyl.
14. A system as defined in claim 13 , wherein R 1 is methyl.
15. A system as defined in claim 11 , wherein at least one of the ligands is a unsubstituted or substituted pyridine.
16. A system as defined in claim 15 , wherein at least one of the ligands is a monosubstituted pyridine.
17. A system as defined in claim 1 , wherein the sample solution is blood obtained from the finger of a user.
18. A system as defined in claim 1 , wherein the sample fluid is blood obtained from a region of a user having a lower nerve end density as compared to a fingertip.
19. A system as defined in claim 18 , wherein the region of the user having a lower nerve end density as compared to a fingertip is selected from the group consisting of: a forearm region, and a thigh region.
20. A system as defined in claim 1 , wherein the reagent layer comprises an electron carrier comprising ferricyanide or ferrocyanide.
21. A system as defined in claim 1 , wherein the sample chamber is sized to contain a volume of no more than 1 μL of the sample fluid.
22. A system as defined in claim 1 , wherein the sample chamber is sized to contain a volume of no more than 0.5 μL of the sample fluid.