Devices, systems, and methods for measuring analytes in interstitial fluid
An analyte monitor includes a controller including a processor coupled to a memory. The memory has instructions stored therein that, when executed by the processor, cause the controller to: provide a working electrode voltage to a working electrode of an analyte sensor; selectively provide a first counter electrode voltage and a second counter electrode voltage to a counter electrode of the analyte sensor; and provide a guard ring voltage to a guard ring associated with the working electrode. The analyte monitor further includes a current measurement circuit coupled to the controller and configured to measure current flow to the working electrode and a reference resistor electrically coupled between the working electrode and the guard ring associated with the working electrode. Other monitors, systems, sensors, and methods are disclosed.
1. An analyte monitor, comprising:
a working electrode voltage source configured to provide a working electrode voltage to a working electrode;
a counter electrode voltage source configured to provide one or more counter electrode voltages to a counter electrode;
a guard ring voltage source configured to provide a guard ring voltage to a guard ring;
a current measurement circuit configured to measure current flow from the working electrode voltage source to the working electrode; and
a controller including at least one processor coupled to a memory, the memory including instructions stored therein that, when executed by the at least one processor, perform at least one integrity check comprising:
providing a first instruction to the working electrode voltage source to provide the working electrode voltage to the working electrode of an analyte sensor;
providing a second instruction to the counter electrode voltage source to provide a first counter electrode voltage or a second counter electrode voltage to the counter electrode of the analyte sensor,
providing a third instruction to the guard ring voltage source to provide the guard ring voltage to the guard ring that at least partially surrounds a contact region of the working electrode,
wherein the working electrode voltage source, the counter electrode voltage source, and the guard ring voltage source are separate and distinct voltage sources;
measuring the current flow by the current measurement circuit; and
determining that the analyte monitor is faulty based on the current flow.
2. The analyte monitor of claim 1 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to measure an analyte concentration by:
applying the working electrode voltage to the working electrode,
applying the first counter electrode voltage to the counter electrode, wherein the first counter electrode voltage is independent of and not equal to the working electrode voltage, and
applying the guard ring voltage to the guard ring, wherein the guard ring voltage is independent of and equal to the working electrode voltage.
3. The analyte monitor of claim 2 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to generate a signal in response to measured current flow to the working electrode exceeding a predetermined amperage during measurement of the analyte concentration.
4. The analyte monitor of claim 1 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to perform a first integrity check by:
applying the working electrode voltage to the working electrode,
applying the second counter electrode voltage to the counter electrode, wherein the second counter electrode voltage is equal to the working electrode voltage, and
applying the guard ring voltage to the guard ring, wherein the guard ring voltage is equal to the working electrode voltage.
5. The analyte monitor of claim 4 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to generate a signal in response to measured current flow to the working electrode exceeding a predetermined amperage during the first integrity check.
6. The analyte monitor of claim 5 , wherein the predetermined amperage is greater than 20 nanoamperes during the first integrity check.
7. The analyte monitor of claim 4 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to apply a reference electrode voltage equal to the second counter electrode voltage to a reference electrode of the analyte sensor during the first integrity check.
8. The analyte monitor of claim 1 , wherein:
the memory further comprises instructions that, when executed by the at least one processor, cause the controller to;
selectively provide a first guard ring voltage and a second guard ring voltage to the guard ring;
the memory further comprises instructions that, when executed by the at least one processor, cause the controller to perform the at least one integrity check by:
applying the second counter electrode voltage to the counter electrode, wherein the second counter electrode voltage is equal to the working electrode voltage, and
applying the second guard ring voltage to the guard ring, wherein the second guard ring voltage is not equal to the working electrode voltage.
9. The analyte monitor of claim 8 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to generate a signal in response to the measured current flow to the working electrode exceeding a first predetermined amperage or being less than a second predetermined amperage during the at least one integrity check.
10. The analyte monitor of claim 9 , wherein the first predetermined amperage is at least 2% greater than a difference between the working electrode voltage and the second guard ring voltage divided by a resistance of a reference resistor, and the second predetermined amperage is at least 2% less than a difference between the working electrode voltage and the second guard ring voltage divided by the resistance of the reference resistor during the at least one integrity check.
11. The analyte monitor of claim 8 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to apply a reference electrode voltage equal to the second counter electrode voltage to a reference electrode of the analyte sensor during the at least one integrity check.
12. An analyte monitoring system, comprising:
an analyte sensor having a working electrode and a counter electrode;
a guard ring surrounding at least a portion of a contact region of the working electrode;
a reference resistor electrically coupled between the working electrode and the guard ring; and
an analyte transmitter coupled to the analyte sensor, the analyte transmitter including:
a working electrode voltage source;
a counter electrode voltage source;
a guard ring voltage source;
a current measurement circuit configured to measure current flow from the working electrode voltage source to the working electrode; and
a controller including at least one processor coupled to a memory, the memory having instructions stored therein that, when executed by the at least one processor, perform at least one integrity check comprising:
providing a first instruction to the working electrode voltage source to provide a working electrode voltage to the working electrode;
providing a second instruction to the counter electrode voltage source to selectively provide a first counter electrode voltage and a second counter electrode voltage to the counter electrode,
wherein the first counter electrode voltage is indicative of an analyte monitoring mode of the analyte monitor and the second counter electrode voltage is indicative of an integrity check of the analyte monitor;
providing a third instruction to the guard ring voltage source to provide a guard ring voltage to the guard ring,
wherein the working electrode voltage source, the counter electrode voltage source, and the guard ring voltage source are separate and distinct voltage sources;
measuring the current flow by the current measurement circuit; and
determining that the analyte monitor is faulty based on the current flow.
13. The analyte monitoring system of claim 12 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to measure an analyte concentration by:
applying the working electrode voltage to the working electrode,
applying the first counter electrode voltage to the counter electrode,
wherein the first counter electrode voltage is not equal to the working electrode voltage, and
applying the guard ring voltage to the guard ring, wherein the guard ring voltage is equal to the working electrode voltage.
14. The analyte monitoring system of claim 13 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to generate a signal in response to measured current flow to the working electrode exceeding a predetermined amperage during measurement of the analyte concentration.
15. The analyte monitoring system of claim 13 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to perform a first integrity check by:
applying the working electrode voltage to the working electrode,
applying the second counter electrode voltage to the counter electrode,
wherein the second counter electrode voltage is equal to the working electrode voltage, and
applying the guard ring voltage to the guard ring, wherein the guard ring voltage is equal to the working electrode voltage.
16. The analyte monitoring system of claim 15 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to generate a signal in response to measured current flow to the working electrode exceeding a predetermined amperage during the first integrity check.
17. The analyte monitoring system of claim 16 , wherein the predetermined amperage is greater than 20.0 nanoamperes.
18. The analyte monitoring system of claim 15 , wherein the analyte sensor has a reference electrode, and wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to apply a reference electrode voltage equal to the second counter electrode voltage to the reference electrode during the first integrity check.
19. The analyte monitoring system of claim 13 , wherein:
the memory has instructions stored therein that, when executed by the at least one processor, cause the controller to:
selectively provide a first guard ring voltage and a second guard ring voltage to the guard ring; and
perform the at least one integrity check by:
applying the second counter electrode voltage to the counter electrode, wherein the second counter electrode voltage is equal to the working electrode voltage, and
applying the second guard ring voltage to the guard ring, wherein the second guard ring voltage is not equal to the working electrode voltage.
20. The analyte monitoring system of claim 19 , wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to generate a signal in response to measured current flow to the working electrode exceeding a first predetermined amperage or being less than a second predetermined amperage during the at least one integrity check.
21. The analyte monitoring system of claim 20 , wherein the first predetermined amperage is at least 2% greater than a difference between the working electrode voltage and the second guard ring voltage divided by a resistance of the reference resistor, and the second predetermined amperage is at least 2% less than a difference between the working electrode voltage and the second guard ring voltage divided by the resistance of the reference resistor during the at least one integrity check.
22. The analyte monitoring system of claim 19 , wherein the analyte sensor has a reference electrode, and wherein the memory further comprises instructions that, when executed by the at least one processor, cause the controller to apply a reference electrode voltage equal to the first counter electrode voltage to the reference electrode during the at least one integrity check.
23. A method of operating an analyte monitoring system, comprising:
providing an analyte sensor having a working electrode and a counter electrode;
providing a guard ring surrounding at least a portion of a contact region of the working electrode;
providing a reference resistor coupled between the working electrode and the guard ring;
providing a first instruction, by at least one processor, to a working electrode voltage source to apply a working electrode voltage to the working electrode;
providing a second instruction, by the at least one processor, to a counter electrode power source to apply one of a first counter electrode voltage or a second counter electrode voltage to the counter electrode;
providing a third instruction, by the at least one processor, to a counter electrode voltage source to apply at least a first guard ring voltage to the guard ring from a guard ring voltage source,
wherein the working electrode voltage source, the counter electrode voltage source, and the guard ring voltage source are separate and distinct voltage sources; and
measuring current flow to the working electrode by an ammeter disposed between the working electrode voltage source and the working electrode.
24. The method of claim 23 , further comprising measuring an analyte concentration by:
applying the first counter electrode voltage to the counter electrode, wherein the first counter electrode voltage is not equal to the working electrode voltage, and
applying the first guard ring voltage to the guard ring, wherein the first guard ring voltage is equal to the working electrode voltage.
25. The method of claim 23 , further comprising performing a first integrity check by:
applying the second counter electrode voltage to the counter electrode, and
applying the first guard ring voltage to the guard ring,
wherein the second counter electrode voltage and the first guard ring voltage are equal to the working electrode voltage.
26. The method of claim 23 , further comprising performing a second integrity check by:
applying the second counter electrode voltage to the counter electrode, wherein the second counter electrode voltage is equal to the working electrode voltage, and
applying a second guard ring voltage to the guard ring, wherein the second guard ring voltage is not equal to the working electrode voltage.