Devices, systems and methods for measuring analytes in interstitial fluid

Abstract

To provide improved systems, methods and apparatus for confirming proper operation of CGM transmitters and biosensors.SOLUTION: 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.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 933,308, filed November 8, 2019, entitled "DEVICES, SYSTEMS, AND METHODS FOR MEASURING ANALYTES IN INTERSTITIAL FLUID," the disclosure of which is incorporated herein by reference in its entirety for all purposes.

[0002] The present disclosure relates to devices, systems, and methods adapted to measure analytes in interstitial fluid. [Background technology]

[0003] Continuous analyte detection in in vivo and / or in vitro samples, such as continuous glucose monitoring (CGM), has become a routine detection operation, particularly in diabetes care. By providing real-time glucose concentrations, therapeutic / clinical actions can be applied in a more timely manner, leading to better control of glycemic conditions.

[0004] During CGM operation, a biosensor is typically inserted subcutaneously and operates continuously in an environment surrounded by tissue and interstitial fluid. The subcutaneously inserted biosensor provides a signal to the wireless CGM transmitter of the CGM sensor device, which indicates the user's blood glucose level. These measurements may be taken automatically multiple times throughout the day (e.g., every few minutes or at other intervals).

[0005] The wireless CGM transmitter may be attached to the outer surface of the user's skin, such as the abdomen or back of the upper arm, while the biosensor is inserted through the skin to contact the interstitial fluid.

[0006] To ensure accurate glucose measurements, CGM devices may periodically perform self-tests to verify proper operation of the biosensor and CGM transmitter. Self-test systems may require additional switches and other hardware, increasing the complexity and cost of the CGM transmitter. Therefore, improved systems, methods, and apparatus for verifying proper operation of the CGM transmitter and biosensor are desirable. Summary of the Invention

[0007] According to a first aspect, an analyte monitor is disclosed. The analyte monitor includes a controller including a processor coupled to a memory, the memory having instructions stored therein that, when executed by the processor, cause the controller to: provide a working electrode voltage to a working electrode of the 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 at least partially surrounding a contact area of ​​the working electrode. The analyte monitor also includes a current measurement circuit coupled to the controller configured to measure a current to the working electrode. The analyte monitor further includes a reference resistor electrically coupled between the working electrode and the guard ring. The memory further includes instructions that, when executed by the processor, cause the controller to perform at least one integrity check by applying the working electrode voltage to the working electrode, applying a first counter electrode voltage or a second counter electrode voltage to the counter electrode, applying a guard ring voltage to the guard ring, and measuring the current to the working electrode using the current measurement circuit.

[0008] According to a second aspect, an analyte monitoring system is disclosed. The analyte monitoring system includes: an analyte sensor having a working electrode and a counter electrode; a guard ring surrounding at least a portion of the contact area 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 includes a controller including a processor coupled to a memory, the memory having instructions stored therein that, when executed by the processor, cause the controller to: provide a working electrode voltage to the working electrode of the analyte sensor, selectively provide a first counter electrode voltage and a second counter electrode voltage to the counter electrode of the analyte sensor, and provide a guard ring voltage to the guard ring. The analyte transmitter also includes a current measurement circuit coupled to the controller and configured to measure a current to the working electrode. The memory further includes instructions that, when executed by the processor, cause the controller to perform at least one consistency check by: applying a working electrode voltage to the working electrode, applying a first counter electrode voltage or a second counter electrode voltage to the counter electrode, applying a guard ring voltage to the guard ring, and measuring a current to the working electrode using a current measurement circuit.

[0009] In a third aspect, a method of operating an analyte monitoring system is disclosed, the method including: providing an analyte sensor having a working electrode and a counter electrode; providing a guard ring surrounding at least a portion of a contact area of ​​the working electrode; providing a reference resistor coupled between the working electrode and the guard ring; applying a working electrode voltage to the working electrode; selectively applying one of a first counter electrode voltage and a second counter electrode voltage to the counter electrode; applying at least a first guard ring voltage to the guard ring; and measuring a current to the working electrode.

[0010] In another aspect, an analyte sensor configured to be attached to the skin is disclosed, the analyte sensor including: a working electrode; a guard ring surrounding at least a portion of a contact area of ​​the working electrode; and a reference resistor coupled between the working electrode and the guard ring.

[0011] Further aspects, features, and advantages of the present disclosure will be readily apparent from the following description, which sets forth several exemplary embodiments and examples. The present disclosure is also capable of other different embodiments, and its several details may be modified in various respects without departing from its scope. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. The present disclosure covers all modifications, equivalents, and alternatives falling within the scope of the claims. [Brief explanation of the drawings]

[0012] The drawings described below are for illustrative purposes only and are not necessarily drawn to scale. The drawings are not intended to limit the scope of the present disclosure in any way. The same numerals are used throughout to refer to the same or similar elements.

[0013] [Figure 1A] FIG. 1A shows a partial cross-sectional side view of a glucose monitoring system including a glucose sensor attached to the skin and a glucose transmitter shown separated from the glucose sensor, according to one or more embodiments.

[0014] [Figure 1B] FIG. 1B shows a bottom view of a glucose transmitter according to one or more embodiments.

[0015] [Figure 1C] FIG. 1C shows a partial cross-sectional side view of a glucose monitoring system including a glucose sensor attached to a glucose transmitter according to one or more embodiments.

[0016] [Figure 2] FIG. 2 schematically illustrates a portion of a glucose monitoring system including a glucose sensor according to one or more embodiments disclosed herein.

[0017] [Figure 3] FIG. 3 schematically illustrates a portion of a glucose monitoring system including a glucose sensor in operation according to one or more embodiments disclosed herein.

[0018] [Figure 4] FIG. 4 schematically illustrates a portion of a glucose monitoring system including a glucose sensor in a first analysis state according to one or more embodiments disclosed herein.

[0019] [Figure 5] FIG. 5 schematically illustrates a portion of a glucose monitoring system including a glucose sensor in a second analysis state according to one or more embodiments disclosed herein.

[0020] [Figure 6] FIG. 6 schematically illustrates a portion of a glucose monitoring system including a glucose sensor according to one or more embodiments disclosed herein.

[0021] [Figure 7] FIG. 7 shows a top view of a glucose sensor with a resistor connected between the working electrode and the guard ring according to one or more embodiments disclosed herein.

[0022] [Figure 8] FIG. 8 shows a flowchart of a method of operating a glucose monitoring system according to one or more embodiments disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0023] A continuous analyte monitoring (CAM) system can monitor the current between two or more points in interstitial fluid to determine the analyte concentration (e.g., glucose concentration) in the interstitial fluid. The CAM system can include an analyte transmitter electrically coupled to an analyte sensor (e.g., a glucose sensor). The analyte transmitter can include an analog front end having contact areas that electrically couple to contact areas of the electrodes of the analyte sensor, such as a working electrode, a counter electrode, a reference electrode, and / or the like, which creates an electrical connection between the CAM transmitter and the electrodes of the analyte sensor.

[0024] The analyte sensor may be coupled to the base plate at a contact area of ​​the base plate. The base plate may be attached to a user's skin, and the analyte transmitter may be coupled to the base plate. The needle of the analyte sensor extends from the base plate through the user's skin and is configured for subcutaneous placement to contact the user's interstitial fluid. The needle includes electrodes of the analyte sensor, such as a working electrode, a counter electrode, and a reference electrode, and contacts these electrodes with the interstitial fluid beneath the user's skin. The analyte transmitter and / or the base plate may include one or more guard rings at least partially surrounding the contact areas of the working and / or reference electrodes of the analyte sensor. For example, in some embodiments, the guard rings may surround and / or substantially surround 50% or more of the electrode contact areas.

[0025] During CAM, a voltage is applied between the working and counter electrodes, and the current between the electrodes is measured. The current between the electrodes is proportional to the analyte (e.g., glucose) concentration in the interstitial fluid. The same voltage applied to the working electrode may be applied to a guard ring associated with the working electrode to prevent current flow through contaminants on the base plate and / or to prevent the analyte transmitter from interfering with the current measurement through the interstitial fluid. The current through the interstitial fluid may be very small, such as in the nanoampere range, thereby making the analyte monitoring system very sensitive. Consistency checks (e.g., self-diagnostic routines) may be performed by the CAM system to ensure the system is operating accurately.

[0026] Embodiments of the analyte monitoring system disclosed herein may include a reference resistor electrically coupled between a guard ring (associated with the working electrode) and the working electrode. During a first consistency check, the voltages applied to the working electrode, guard ring, and counter electrode are set equal. If the analyte transmitter and / or analyte sensor are operating properly, there will be little or no current between the guard ring and the electrode because they are all set to the same voltage. Any current or current above a predetermined (e.g., threshold) amperage may indicate a fault in the analyte monitoring system (e.g., due to electrical connection errors or contamination of the analyte transmitter, base plate, or sensor).

[0027] During the second consistency check, the voltages applied to the working electrode and counter electrode may be equal, while the voltage applied to the guard ring may be different from the voltage applied to the working electrode. If the analyte transmitter and / or analyte sensor are operating properly, little or no current should flow between the working electrode and counter electrode. However, current should flow between the guard ring and working electrode only through the reference resistor. The magnitude of the current should be equal to the voltage difference between the working electrode and guard ring divided by the resistance of the reference resistor. If any other current is measured, a fault in the analyte monitoring system may exist (e.g., due to electrical connection errors or contamination of the analyte transmitter, base plate, or sensor).

[0028] These and other embodiments are described in detail with reference to Figures 1A-8 herein. Although primarily described with respect to determining glucose concentrations using a glucose monitoring system, the embodiments described herein may be used with other analyte monitoring systems (e.g., cholesterol, lactate, uric acid, alcohol, or other analyte monitoring systems).

[0029] Reference is now made to FIG. 1A , which illustrates a partial cross-sectional side view of a glucose monitoring system 100 including a glucose transmitter 102 and a glucose sensor assembly 104. The glucose transmitter 102 is shown separated from the glucose sensor assembly 104 to illustrate various features described below, and the glucose sensor assembly 104 is shown attached to the skin 106. Reference is also made to FIG. 1B , which illustrates a bottom view of one embodiment of the glucose transmitter 102. Interstitial fluid 108 is located below the skin 106. The components of the glucose monitoring system 100 and the skin 106 may not be drawn to scale. The glucose sensor assembly 104 may include a substrate 110 (e.g., a base plate) on which the components of the glucose sensor assembly 104 are located. Portions of the substrate 110 may be made of a non-conductive material, such as plastic, ceramic, or another suitable material. In some embodiments, the substrate 110 may include a laminate material. The substrate 110 may include electrical traces (not shown) that conduct electrical current to components within or attached to the substrate 110. An adhesive 112 such as acrylic, silicone, etc. may attach the substrate 110 to the outer surface of the skin 106 .

[0030] 1A-1B, the glucose sensor assembly 104 may include a sensor electrode contact area 114A, including a working electrode contact area 116A, a reference electrode contact area 118A, and a counter electrode contact area 120A, for contacting a working electrode 117, a reference electrode 119, and a counter electrode 121, respectively, as further described below. Fewer or more electrode contact areas and / or electrodes, and / or other suitable electrode configurations may be used. For example, in some embodiments, a second working electrode (e.g., a background electrode) may be used. The electrodes 117, 119, and 121 may be formed with and / or enclosed within needles 122 configured to be positioned at least partially below the skin 106 in the interstitial fluid 108 such that the electrodes 117, 119, and 121 can contact the interstitial fluid and pass current through the sensor electrode contact areas 116A, 118A, and 120A.

[0031] The glucose transmitter 102 may include a surface 124 on which the transmitter contact area 114B is located. The transmitter contact area 114B may include corresponding individual contact areas as the sensor electrode contact area 114A. For example, the transmitter contact area 114B may include a working electrode contact area 116B, a reference electrode contact area 118B, and a counter electrode contact area 120B. The individual contact areas of the sensor electrode contact area 114A and the transmitter contact area 114B may have any shape, such as a circle, an oval, a square, or a rectangle.

[0032] In addition to the contact areas described above, the glucose transmitter 102 and / or glucose sensor assembly 104 may have guard rings that at least partially surround at least one of the contact areas. In the embodiment illustrated in Figures 1A and 1B, the glucose sensor assembly 104 includes a working electrode guard ring 128A that surrounds at least a portion of the working electrode contact area 116A. The glucose sensor assembly 104 may also include a reference electrode guard ring 130A that surrounds at least a portion of the reference electrode contact area 118A. The glucose transmitter 102 may include a working electrode guard ring 128B that surrounds at least a portion of the working electrode contact area 116B, and a reference electrode guard ring 130B that surrounds at least a portion of the reference electrode contact area 118B.

[0033] During operation of glucose monitoring system 100, glucose transmitter 102 and glucose sensor assembly 104 may be attached together, as shown in FIG. 1C , such that transmitter contact area 114B is in electrical contact with sensor electrode contact area 114A. The guard rings of glucose transmitter 102 may also be in electrical contact with the respective guard rings of glucose sensor assembly 104. When glucose sensor assembly 104 is attached to glucose transmitter 102, working electrode contact areas 116A and 116B may be in electrical contact with working electrode 117, reference electrode contact areas 118A and 118B may be in electrical contact with reference electrode 119, and counter electrode contact areas 120A and 120B may be in electrical contact with counter electrode 121. Additionally, working electrode guard ring 128A and working electrode guard ring 128B may form guard ring 128, and reference electrode guard ring 130A and reference electrode guard ring 130B may form guard ring 130. Sensor electrode contact area 114A and transmitter contact area 114B may be collectively referred to as electrode contact area 114. In some embodiments, guard ring 128 and / or guard ring 130 may have an annular shape. In some embodiments, at least one of guard ring 128 and / or guard ring 130 may have a circular, oval, rectangular, or any other suitable shape.

[0034] The electrodes 117, 119, and 121 may apply a voltage and / or pass a current through the interstitial fluid 108 via the needle 122. For example, during operation of the glucose monitoring system 100, a current may flow between the working electrode 117 and the counter electrode 121. The reference electrode 119 may have no or little current and may function to set the voltage of the counter electrode 121. As described herein, the current between the working electrode 117 and the counter electrode 121 is proportional to the glucose concentration of the interstitial fluid 108. Thus, the glucose monitoring system 100 may measure the current between the working electrode 117 and the counter electrode 121 to determine the glucose concentration of the interstitial fluid 108.

[0035] The guard ring 128 prevents stray currents from flowing on the surface 124 of the glucose transmitter 102 and / or the surface of the substrate 110 and being interpreted as current flowing through the interstitial fluid 108. The guard ring 128 may include a conductive ring that surrounds at least a portion of the working electrode contact area 116 and may contact the surface 124. During operation of the glucose sensor assembly 104, the guard ring 128 may operate at the same voltage as the working electrode 117. Because the guard ring 128 and the working electrode 117 operate at the same voltage, no current flows between the working electrode 117 and the guard ring 128. Therefore, only current flowing through the interstitial fluid 108 flows through the working electrode 117.

[0036] Reference is further made to Figure 2, which schematically illustrates one embodiment of a portion of a glucose monitoring system 100 provided herein. The glucose monitoring system 100 illustrated in Figure 2 may include a glucose transmitter 102 electrically coupled to a glucose sensor assembly 104. The glucose transmitter 102 may include an analog front end 220 that may be configured to electrically couple to the components of the glucose sensor assembly 104.

[0037] The glucose transmitter 102 may include a controller 222 configured to control and monitor components within the glucose monitoring system 100 and / or the analog front end 220. The controller 222 may include a processor 222P coupled to a memory 222M. The memory 222M may have instructions stored therein that, when executed by the processor 222P, cause the controller 222 to control and / or monitor various components of the glucose monitoring system 100 described herein.

[0038] The processor 222P may be a computational resource such as, but not limited to, a microprocessor, a microcontroller, an embedded microcontroller, a digital signal processor (DSP), a field programmable gate array (FPGA) configured to operate as a microcontroller, etc. The memory 222M may be any suitable type of memory, such as, but not limited to, one or more of volatile memory and / or non-volatile memory.

[0039] The analog front end 220 may also include multiple power supplies configured to be electrically coupled to the components of the glucose sensor assembly 104 and controlled by the controller 222. For example, the power supplies may bias components such as the electrodes 117, 119, and 121 at different predetermined voltages. In the embodiment shown in FIG. 2, the analog front end 220 may include three power supplies, individually referred to as a working electrode (WE) source 224, a guard source 226, and a counter electrode (CE) source 228. The analog front end 220 may include other components not shown. For example, the analog front end 220 may include a component that monitors the voltage of the reference electrode 119.

[0040] The WE source 224 generates the working electrode voltage V WE to the working electrode contact area 116A of the glucose sensor assembly 104. The WE source 224 has a control input 224A coupled to the controller 222 and a working electrode voltage V WE For example, the controller 222 may send commands to the WE source 224 via the control input 224A, which in turn may cause the WE source 224 to apply a working electrode voltage V via the output 224B and provide a current I21. WE can be output.

[0041] The analog front end 220 may also include a current measurement circuit (e.g., an ammeter) 230 configured to measure the output current I21 of the WE source 224, which may be the current flowing through the working electrode 117. The ammeter 230 may generate signals indicative of the amperage of the current I21 and send these signals to the controller 222. In some embodiments, the memory 222M may include instructions that, when executed by the processor 222P, cause the controller 222 to generate a signal in response to the measured current of the ammeter 230 exceeding a predetermined (e.g., threshold) amperage or being outside a predetermined (e.g., threshold) amperage range. For example, in some embodiments, the controller 222 may be configured to generate a signal in response to the current I21 measured by the ammeter 230 being greater than a first predetermined amperage or less than a second predetermined amperage. The signal generated by the controller 222 may indicate that an error condition exists in the glucose monitoring system 100.

[0042] The CE source 228 may be configured to provide two or more counter electrode voltages to the counter electrode contact area 120. The CE source 228 may include a control input 228A and an output 228B that output two or more counter electrode voltages. The control input 228A may be coupled to the controller 222 and may receive instructions regarding the voltage to output at the output 228B. The CE source 228 provides at least a first counter electrode (CE) voltage V CE1 and the second CE voltage V CE2 to the counter electrode 121. For example, the controller 222 may be configured to send a command to the CE source 228 via the control input 228A to cause the CE source 228 to output a first CE voltage V CE1 or the second CE voltage V CE2 At least one of the following may be output.

[0043] In some embodiments, the CE source 228 generates a first CE voltage V during normal operation of the glucose monitoring system 100. CE1CE source 228 may output a second CE voltage V when glucose monitoring system 100 is in an analysis (e.g., self-diagnostic) state as described herein. CE2 In some embodiments, the first CE voltage V CE1 is the working electrode voltage V WE The second CE voltage V is not equal to CE2 is the working electrode voltage V WE Other suitable voltages may be used.

[0044] The guard source 226 may be configured to apply one or more guard ring voltages to the guard ring 128. In the embodiment illustrated in FIG. 2, the guard source 226 applies at least a first guard ring voltage V G1 and the second guard ring voltage V G2 to the guard ring 128. The guard source 226 may include a control input 226A coupled to the controller 222 and an output 226B configured to be electrically coupled to the guard ring 128. The output 226B may be configured to output at least a first guard ring voltage V G1 or the second guard ring voltage V G2 For example, the controller 222 may send a command to the guard source 226 via the control input 226A to instruct the guard source 226 to apply a first guard ring voltage V G1 or the second guard ring voltage V G2 At least one of the signals may be output to the guard ring 128.

[0045] In some embodiments, the first guard ring voltage V G1 is the working electrode voltage V WE and the second guard ring voltage V G2 is the working electrode voltage V WE . Other suitable voltages may be used. In some embodiments, guard source 226 generates a first guard ring voltage V when glucose monitoring system 100 is in an operational state. G1Guard source 226 may output a second guard ring voltage V when glucose monitoring system 100 is in the analysis state. G2 In some embodiments, output 226B of guard source 226 may have a low impedance to source or sink current (e.g., current I21) when glucose monitoring system 100 is in an analysis state as described herein.

[0046] The reference resistor R21 may be configured to be electrically coupled between the working electrode 117 (e.g., working electrode contact area 116A and / or 116B) and, for example, the guard ring 128. In some embodiments, the reference resistor R21 may be electrically coupled between the output of the ammeter 230 and the output 226B of the guard source 226. In some embodiments, the reference resistor R21 may have a high resistance value, such as, for example, about 5 MΩ with an accuracy of 0.5 to 1%. The reference resistor R21 may have other suitable resistance and accuracy values. In some embodiments, the reference resistor R21 may be located within the glucose transmitter 102, while in other embodiments, the reference resistor R21 may be located within the glucose sensor assembly 104 (e.g., as shown in glucose sensor assembly 704 of FIG. 7).

[0047] In some embodiments, glucose monitoring system 100 can operate in at least an operating state, a first analysis state, and a second analysis state. When glucose monitoring system 100 is in the operating state, it measures the glucose concentration of interstitial fluid 108 ( FIG. 1A ), as described herein. The glucose concentration in interstitial fluid 108 is proportional to the conductivity of the interstitial fluid 108. Therefore, the glucose concentration in interstitial fluid 108 can be continuously measured by continuously measuring (e.g., under a constant bias) the current I21 flowing through working electrode contact area 116A. For example, ammeter 230 can continuously measure current I21. Current I21 can be equal to the current flowing between working electrode 117 and counter electrode 121 plus the current flowing through reference resistor R21. In normal operation, in which glucose monitoring system 100 monitors glucose concentration, the working electrode voltage V WE and the first guard ring voltage V G1 may be equal, so no current flows through the reference resistor R21.

[0048] In all states of the glucose monitoring system 100 and glucose transmitter 102 described herein, the WE source 224 supplies the working electrode voltage V WE For example, the controller 222 may send a command to the WE source 224, causing the WE source 224 to apply a working electrode voltage V on output 224B. WE In some embodiments, the working electrode voltage V WE may be approximately 1.5v, although other suitable values ​​(e.g., greater than 1.5 volts, 1.5 volts, 1.0 volts, 0.5 volts, less than 0.1 volts, etc.) may be used. Output 224B of WE source 224 may have a low impedance so that WE source 224 can source and / or sink current I21.

[0049] The glucose transmitter 102 may be in one or more analytical states and may perform one or more self-diagnostic or integrity checks. The glucose transmitter 102 may also be in an operational or normal state when the glucose transmitter 102 processes a signal from the glucose sensor assembly 104 to measure the glucose concentration. Example states of the outputs of the WE source 224, guard source 226, and CE source 228 are summarized by their relative values ​​in Table 1. V for different states WE , V CE1 , V CE2 , V G1 , and V G2 Exemplary values ​​for are shown in Table 2. Other suitable voltages may be used.

[0050] [Table 1]

[0051] [Table 2]

[0052] 3, an embodiment of glucose monitoring system 100 configured in an operational state is shown schematically. When glucose monitoring system 100 is in an operational state, CE source 228 applies a first CE voltage V to counter electrode contact area 120A. CE1 For example, the controller 222 may send a command to the CE source 228 via the control input 228A to cause the CE source 228 to apply a first CE voltage V at the output 228B. CE1 The first CE voltage V output by the CE source 228 when the glucose monitoring system 100 is in an operational state may be CE1 is the working electrode voltage V WE For example, the first counter electrode voltage V CE1 is the working electrode voltage V WE or the first counter electrode voltage V CE1 is the working electrode voltage V WETherefore, a current can flow between the working electrode 117 and the counter electrode 121. In some embodiments, the working electrode voltage V WE and the first counter electrode voltage V CE1 In some embodiments, the difference between the working electrode voltage V WE is about 1.5V, and the first counter electrode voltage V CE1 is approximately 1.0 V. Other suitable voltages may be used.

[0053] When glucose monitoring system 100 is in an operational state, guard source 226 generates a first guard ring voltage V G1 may be applied to the guard ring 128. As mentioned above, the first guard ring voltage V G1 is the working electrode voltage V WE For example, the controller 222 may send a command to the guard source 226 via a control input 226A to cause the guard source 226 to generate a first guard ring voltage V at an output 226B. G1 The first guard ring voltage V G1 is the working electrode voltage V WE By setting ⁢ ⁢ ⁢ ⁢ ⁢ ⁢ equal to ⁢ ...

[0054] To ensure accuracy, glucose monitoring system 100 may perform periodic self-tests (e.g., consistency checks). Conventional glucose monitoring devices may include switches or the like for use during self-tests. The glucose monitoring system 100 described herein includes a reference resistor R21 that may be permanently electrically coupled between working electrode contact area 116A and guard ring 128. Thus, the glucose monitoring system 100 described herein does not require additional switching circuitry.

[0055] 4, one embodiment of analog front end 220 is shown in a schematic diagram in a first analysis state for performing a first consistency check. When analog front end 220 is in the first analysis state, the voltages of the electrodes are set to be equal by controller 222. Thus, WE source 224, guard source 226, and CE source 228 are set to V WE =V G1 =V CE2 In some embodiments, all voltages may be set to 1.5V. Because the voltages of the working electrode 117, guard ring 128, and counter electrode 121 are the same, no current should flow between the electrodes. Therefore, the ammeter 230 may not measure any current. In response to the ammeter 230 measuring a current, the controller 222 may generate a signal indicating a fault in the glucose monitoring system 100. In some embodiments, the controller 222 may generate a signal in response to the ammeter 230 measuring a current greater than a predetermined (e.g., threshold) amperage. In some embodiments, the predetermined amperage that causes the controller 222 to generate a signal (e.g., an error message, fault signal, and / or alarm) may be approximately 10-20 nanoamperes or greater, although other suitable values ​​may be used. For example, some stray current associated with a component may flow such that the stray current does not adversely affect the glucose monitoring system 100. In some embodiments, the predetermined amperage that causes controller 222 to generate a signal can be set based on the tolerances in glucose monitoring system 100 (FIG. 1A).

[0056] 5, one embodiment of analog front end 220 is shown in a schematic diagram in a second analysis state for performing a second consistency check. When analog front end 220 is in the second analysis state, the voltages of all electrodes are set by controller 222 so that a current I21 is drawn through reference resistor R21. For example, a second CE voltage V CE2 is the working electrode voltage VWE The guard source 226 may be equal to the working electrode voltage V WE Second guard ring voltage V not equal to G2 In some embodiments, the second guard ring voltage V G2 is the working electrode voltage V WE For example, the working electrode voltage V WE can be 1.5V, and the second guard ring voltage V G2 can be 1.0v.

[0057] As described above, when the analog front end 220 is in the second analysis state, a voltage difference exists between the working electrode 117 and the guard ring 128. As shown in Figure 5, this voltage difference exists across the reference resistor R21. The second CE voltage V output by the CE source 228 is CE2 is the working electrode voltage V at the working electrode 117 WE Therefore, no current flows between the working electrode 117 and the counter electrode 121. When the glucose monitoring system 100 is operating correctly, the only current measured by the ammeter 230 is the current I21 through the reference resistor R21. The reference resistor R21 may be a precision resistor and is connected to the working electrode voltage V WE and the second guard ring voltage V G2 can be a precision voltage, such that the accuracy of the resistance and voltage is proportional to the accuracy of the second self-test performed by glucose monitoring system 100. Under ideal conditions, the current measured by ammeter 230 is the voltage difference (V) divided by the resistance of reference resistor R21. WE ~V G2 ).

[0058] Controller 222 may generate a signal (e.g., an error message, a fault signal, and / or an alarm) in response to the current measured by ammeter 230 being greater than a first predetermined (e.g., threshold) amperage and / or less than a second predetermined (e.g., threshold) amperage during the second consistency check. For example, in some embodiments, the first predetermined amperage may be slightly greater (e.g., 2% greater, 5% greater, etc.) than the current measured under ideal conditions, and the second predetermined amperage may be slightly less (e.g., 2% less, 5% less, etc.) than the current measured under ideal conditions. Other suitable predetermined amperages may be used. The signal generated by controller 222 may indicate a fault, such as contamination, in glucose monitoring system 100.

[0059] Reference is now made to Figure 6, which schematically illustrates another embodiment of an analog front end 620 of the glucose monitoring system 100. The analog front end 620 may include digital-to-analog converters (DACs) coupled to the controller 222, which output the voltages described above to the glucose sensor assembly 104. For example, the controller 222 may output digital (e.g., binary) values ​​representing the voltages output by the individual DACs.

[0060] The analog front end 620 shown in FIG. 6 may include a first DAC 640A having a digital input coupled to the controller 222. The analog output of the first DAC 640A may be coupled to a non-inverting input of a first operational amplifier 642A, which may be configured as a buffer. The output of the first operational amplifier 642A may be configured to couple to the working electrode contact area 116. The analog front end 620 may also include a second DAC 640B having a digital input coupled to the controller 222. The analog output of the second DAC 640B may be coupled to a non-inverting input of a second operational amplifier 642B. The output of the second operational amplifier 642B may be configured to couple to the guard ring 128. The second operational amplifier 642B may be configured as a buffer. The analog front end 620 may also include a reference resistor R21 coupled between the output of the ammeter 230 and the output of the second operational amplifier 642B. In some embodiments, the reference resistor R21 can be located in the glucose sensor assembly 104 shown in FIG.

[0061] The analog front end 620 may also include a third DAC 640C having a digital input coupled to the controller 222. The analog output of the third DAC 640C may be coupled to the non-inverting input of a third operational amplifier 642C, which may be configured as a buffer. In some embodiments, the counter electrode contact area 120 and the reference electrode contact area 118 may be coupled together by a switch SW61, which may be controlled by the controller 222. The controller 222 may close the switch SW61 when the analog front end 620 is in the analysis state, and the controller 222 may open the switch SW61 when the analog front end 620 is in the normal operating state. The switch SW61 may be closed when the glucose transmitter 602 is in the analysis state, which applies the counter electrode voltage as the reference electrode voltage. The switch SW61 may be open when the glucose transmitter 602 is in normal operation to measure glucose concentrations. In some embodiments, a similar switching mechanism (not shown) may be included in the glucose transmitter 102 of FIGS. 2-5.

[0062] Analog front end 620 may operate in the same manner as analog front end 220 (FIGS. 2-5). For example, analog front end 620 may operate by varying voltage V WE , V CE1 , V CE2 , V G1 , and V G2 may be output.

[0063] In some embodiments, the reference resistor R21 may be located on or within the glucose sensor assembly 104. Referring to FIG. 7, a top view of the glucose sensor assembly 704 with the reference resistor R21 located thereon is shown. The reference resistor R21 may be electrically connected, for example, between the working electrode contact area 116 and the guard ring 128. Alternatively, the reference resistor R21 may be directly coupled between the working electrode 117 and the guard ring 128 in other embodiments. The glucose transmitter 102 (FIG. 1A) may be electrically coupled to the glucose sensor assembly 704 and function as described herein.

[0064] 8, a flowchart 800 is shown illustrating a method of operating an analyte monitoring system (e.g., glucose monitoring system 100) according to embodiments provided herein. The method includes, at 802, providing an analyte sensor (e.g., glucose sensor assembly 104 or 704) having a working electrode (e.g., working electrode 117), a counter electrode (e.g., counter electrode 121), and a guard ring (e.g., guard ring 128) surrounding at least a portion of the working electrode contact area. The method includes, at 804, providing a reference resistor (e.g., reference resistor R21) electrically coupled between the working electrode and the guard ring of the analyte sensor. The method includes, at 806, determining a working electrode voltage (e.g., working electrode voltage V WE ) to the working electrode of the analyte sensor. At 808, the method includes applying a first counter electrode voltage (e.g., a first CE voltage V CE1 ) and a second counter electrode voltage (e.g., a second CE voltage V CE2) to the counter electrode of the analyte sensor. At 810, the method includes selectively applying at least a first guard ring voltage (e.g., a first guard ring voltage V G1 ) to a guard ring of the analyte sensor. At 812, the method includes measuring a current to the working electrode.

[0065] In some embodiments, the first counter electrode voltage V CE1 and the first guard ring voltage V G1 is the working electrode voltage V WE In other embodiments, the first guard ring voltage V G1 is the working electrode voltage V WE The current to the working electrode 117 can be measured to determine whether the glucose monitoring system 100 is functioning properly (e.g., whether the current is as expected based on the voltages applied to the working electrode 117, counter electrode 121, guard ring 128, and / or reference electrode 119).

[0066] In some embodiments, the reference electrode contact area 118A / 118B may include a guard ring 130 that at least partially surrounds the reference electrode contact area 118A / 118B.

[0067] While the present disclosure is susceptible to various modifications and alternative forms, specific assembly and apparatus embodiments and methods have been shown by way of example in the drawings and are herein described in detail. The invention is not, however, limited to the particular assemblies, apparatus, or methods disclosed herein, but on the contrary, the invention covers all modifications, equivalents, and alternatives falling within the scope of the claims.

Claims

1. an analyte monitor comprising a working electrode, a counter electrode, a guard ring, a current measurement circuit, and a controller; the guard ring is associated with the working electrode; the current measurement circuit is configured to measure the current to the working electrode; the controller is coupled to the current measurement circuit; the controller comprises at least one processor and at least one memory; The at least one memory has instructions stored therein that, when executed by the at least one processor, cause the controller to perform an integrity check including the steps of: applying a working electrode voltage to the working electrode; applying a first counter electrode voltage or a second counter electrode voltage to the counter electrode; and applying a guard ring voltage to the guard ring wherein the integrity check is based on measuring the current to the working electrode using the current measurement circuit. Analyte monitor.

2. The analyte monitor of claim 1 , wherein the guard ring voltage is equal to the working electrode voltage.

3. 10. The analyte monitor of claim 1, wherein the at least one memory further comprises instructions that, when executed by the at least one processor, cause the controller to generate a signal in response to a measured current to the working electrode exceeding a predetermined amperage during measurement of an analyte concentration.

4. The analyte monitor of claim 3 , wherein the predetermined amperage is greater than 20.0 nanoamperes.

5. The analyte monitor of claim 3 , further comprising a reference resistor electrically coupled between the working electrode and the guard ring.

6. 6. The analyte monitor of claim 5, wherein the predetermined number of amplifiers is at least 2% greater than the difference between the working electrode voltage and the guard ring voltage divided by the resistance of the reference resistor.

7. 10. The analyte monitor of claim 1, wherein the second counter electrode voltage is equal to the working electrode voltage.

8. The analyte monitor of claim 1 , wherein the working electrode and the counter electrode are each enclosed within a needle.

9. a working electrode power supply coupled to the working electrode; a counter electrode power supply coupled to the counter electrode; and a power supply for the guard ring coupled to the guard ring; The analyte monitor of claim 1 further comprising:

10. an analyte monitor comprising a working electrode, a counter electrode, a guard ring, and current measurement circuitry; the working electrode is operable to receive a working electrode voltage from at least one power source associated with the analyte monitor; the counter electrode is operable to receive two or more counter electrode voltages from the at least one power source; the guard ring is associated with the working electrode, the guard ring operable to receive a guard ring voltage from at least one power source associated with the analyte monitor; the current measurement circuit is configured to measure the current to the working electrode; wherein the analyte monitor performs an integrity check based on measuring current to the working electrode using the current measurement circuit after applying the working electrode voltage, at least one of the two or more counter electrode voltages, and the guard ring voltage.

11. The at least one power source a working electrode power supply configured to apply the working electrode voltage to the working electrode; a counter electrode power supply configured to apply the two or more counter electrode voltages to the counter electrode; a guard ring power supply configured to apply the guard ring voltage to the guard ring; 11. The analyte monitor of claim 10, comprising:

12. 11. The analyte monitor of claim 10, further comprising a reference resistor electrically coupled between the working electrode and the guard ring.

13. 13. The analyte monitor of claim 12, wherein the reference resistor has a high resistance value of 5 megaohms.

14. 11. The analyte monitor of claim 10, wherein the analyte monitor performs a second integrity check, different from the integrity check, based on measuring current to the working electrode using the current measurement circuit after applying the working electrode voltage, at least one of the two or more counter electrode voltages, and a second guard ring voltage.

15. 15. The analyte monitor of claim 14, wherein the second guard ring voltage is different from the working electrode voltage.

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