Analyte measurement
A method for determining the concentration of an analyte in a sample is disclosed which comprises contacting the sample with a micro electrode which comprises an enzyme capable of reacting with said analyte and a redox mediator which is capable of being converted by being oxidised or reduced by said enzyme once the latter has reacted with the analyte, allowing the analyte to react with the enzyme, then applying a potential across the electrode and measuring the resulting concentration of the converted mediator electrochemically.
1. A method for determining the concentration of an analyte in a sample which comprises contacting the sample with a micro electrode which comprises an enzyme capable of reacting with said analyte and a redox mediator which is capable of being converted by being oxidised or reduced by said enzyme once the latter has reacted with the analyte, allowing the analyte to react with the enzyme, said reaction going to completion or substantially to completion before a potential is applied, then applying a potential across the electrode and measuring the resulting concentration of the converted mediator electrochemically.
2. A method according to claim 1 wherein the resulting concentration is measured from the resulting current.
3. A method according to claim 1 wherein the micro electrode comprises a working electrode, a counter electrode and a reference electrode.
4. A method according to claim 3 wherein the counter electrode and reference electrode are combined.
5. A method according to claim 3 wherein the working electrode is made of palladium, platinum, gold or carbon and the counter electrode is made of carbon, Ag/AgCl, Ag/Ag 2 SO 4 , palladium, gold, platinum, Cu/CuSo 4 , Hg/HgO, Hg/HgCl 2 , Hg/HgSO 4 , or Zu/ZuSO 4 .
6. A method according to claim 1 wherein the mediator is ferricyanide, phenazine ethosulphate, phenazine methosulphate, 1-methoxy phenazine methosulphate, phenylene diamine or ruthenium hexamine.
7. A method according to claim 1 wherein the enzyme is glucose dehydrogenase, cholesterol esterase, horseradish peroxidase, cholesterol dehydrogenase, cholesterol oxidase, lipo protein lipase, glycerol kinase, glycerol dehydrogenase, glycerol-3-phosphate oxidase, lactate oxidase or lactate dehydrogenase.
8. A method according to claim 1 which comprises allowing a time of 0.5 to 180 seconds to elapse after the sample has been applied to the micro electrode before applying a potential across the electrode and making an electrochemical measurement no more than 5 seconds thereafter.
9. A method according to claim 8 wherein the potential applied is from −2 to +2 volt.
10. A method according to claim 8 wherein the measurement is taken 10 to 500 milliseconds after the potential has been applied.
11. A method according to claim 8 wherein 10 to 100 measurements are taken.
12. A method according to claim 1 wherein the micro electrode has previously been calibrated to provide a direct reading.
13. A method according to claim 1 wherein the mediator is present in excess in relation to the analyte.
14. A method of determining the concentration of an analyte in a sample which comprises contacting the sample with a micro electrode which contains an enzyme capable of reacting with said analyte and a redox mediator which is capable of being converted by being oxidised or reduced by said enzyme once the latter has reacted with the analyte, allowing the analyte to react with the enzyme, then applying a potential across the electrode, measuring the resulting current, reversing the potential and measuring the current again, expressing the two currents as a ratio or a percentage and determining the concentration of the analyte directly therefrom.
15. A method according to claim 14 wherein the micro electrode comprises a working electrode, a counter electrode and a reference electrode.
16. A method according to claim 15 wherein the counter electrode and reference electrode are combined.
17. A method according to claim 15 wherein the working electrode is made of palladium, platinum, gold or carbon and the counter electrode is made of carbon, Ag/AgCl, Ag/Ag 2 SO 4 , palladium, gold, platinum, Cu/CuSo 4 , Hg/HgO, Hg/HgCl 2 , Hg/HgSO 4 , or Zu/ZuSO 4 .
18. A method according to claim 14 wherein the mediator is ferricyanide, phenazine ethosulphate, phenazine methosulphate, 1-methoxy phenazine methosulphate, phenylene diamine or ruthenium hexamine.
19. A method according to claim 14 wherein the enzyme is glucose dehydrogenase, cholesterol esterase, horseradish peroxidase, cholesterol dehydrogenase, cholesterol oxidase, lipo protein lipase, glycerol kinase, glycerol dehydrogenase, glycerol-3-phosphate oxidase, lactate oxidase or lactate dehydrogenase.
20. A method according to claim 14 which comprises allowing a time of 0.5 to 60 seconds to elapse after the sample has been applied to the micro electrode before applying a potential across the electrode and making an electrochemical measurement no more than 5 seconds thereafter.
21. A method according to claim 20 wherein the potential applied is from −2 to +2 volt.
22. A method according to claim 20 wherein the measurement is taken 10 to 500 milliseconds after the potential has been applied.
23. A method according to claim 20 wherein 10 to 100 measurements are taken.
24. A method according to claim 14 wherein the micro electrode has previously been calibrated to provide a direct reading.
25. A method according to claim 14 wherein the mediator is present in excess in relation to the analyte.