Application of electrochemical impedance spectroscopy in sensor systems, devices, and related methods
First Claim
1. A method of performing real-time sensor diagnostics on a subcutaneous or implanted sensor of a sensor system, said sensor including at least one working electrode and said sensor system including a microprocessor that is operatively connected to said sensor, the method comprising:
- (a) periodically performing an electrochemical impedance spectroscopy (EIS) procedure to generate multiple sets of impedance-related data for said at least one working electrode;
(b) calculating, by said microprocessor, respective values of a plurality of impedance-related parameters based on said multiple sets of impedance-related data, said plurality of parameters including impedance, phase angle, and Nyquist slope;
(c) based on said respective values, determining, by said microprocessor, whether the sensor is functioning normally, wherein the microprocessor;
(i) performs a first test based on values of real impedance or phase angle;
(ii) performs a second test based on values of respective frequencies at which successive EIS procedures are performed;
(iii) performs a third test based on a comparison of current and post-sensor initialization impedance values at 1 kHz;
(iv) performs a fourth test based on the value of post-sensor initialization impedance at 0.1 Hz;
(v) performs a fifth test based on a global change in the value of Nyquist slope between 0.1 Hz and 1 Hz;
(vi) performs a sixth test based on a change, over time, in the magnitude of real impedance;
(vii) determines that the sensor is functioning normally if at least 3 of said first through sixth tests are satisfied by generating results that fail within respective predetermined criteria, and that the sensor is not functioning normally if less than 3 of said first through sixth tests are satisfied by generating results that fall within respective predetermined criteria,wherein the microprocessor determines that the third test is satisfied if the current value of impedance is less than the post-initialization value of impedance at 1 kHz,wherein the microprocessor determines that the fourth test is satisfied if the value of impedance is less than 300 kOhms at 0.1 Hz during post-initialization sensor operation, andwherein the microprocessor determines that the sixth test is satisfied if the value of real impedance is determined to be globally decreasing over successive EIS runs; and
(d) based on said determination that the sensor is not functioning normally, sending an alert to a user of the sensor, by the microprocessor, that the sensor should be replaced.
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Abstract
A diagnostic Electrochemical Impedance Spectroscopy (EIS) procedure is applied to measure values of impedance-related parameters for one or more sensing electrodes. The parameters may include real impedance, imaginary impedance, impedance magnitude, and/or phase angle. The measured values of the impedance-related parameters are then used in performing sensor diagnostics, calculating a highly-reliable fused sensor glucose value based on signals from a plurality of redundant sensing electrodes, calibrating sensors, detecting interferents within close proximity of one or more sensing electrodes, and testing surface area characteristics of electroplated electrodes. Advantageously, impedance-related parameters can be defined that are substantially glucose-independent over specific ranges of frequencies. An Application Specific Integrated Circuit (ASIC) enables implementation of the EIS-based diagnostics, fusion algorithms, and other processes based on measurement of EIS-based parameters.
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Citations
13 Claims
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1. A method of performing real-time sensor diagnostics on a subcutaneous or implanted sensor of a sensor system, said sensor including at least one working electrode and said sensor system including a microprocessor that is operatively connected to said sensor, the method comprising:
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(a) periodically performing an electrochemical impedance spectroscopy (EIS) procedure to generate multiple sets of impedance-related data for said at least one working electrode; (b) calculating, by said microprocessor, respective values of a plurality of impedance-related parameters based on said multiple sets of impedance-related data, said plurality of parameters including impedance, phase angle, and Nyquist slope; (c) based on said respective values, determining, by said microprocessor, whether the sensor is functioning normally, wherein the microprocessor; (i) performs a first test based on values of real impedance or phase angle; (ii) performs a second test based on values of respective frequencies at which successive EIS procedures are performed; (iii) performs a third test based on a comparison of current and post-sensor initialization impedance values at 1 kHz; (iv) performs a fourth test based on the value of post-sensor initialization impedance at 0.1 Hz; (v) performs a fifth test based on a global change in the value of Nyquist slope between 0.1 Hz and 1 Hz; (vi) performs a sixth test based on a change, over time, in the magnitude of real impedance; (vii) determines that the sensor is functioning normally if at least 3 of said first through sixth tests are satisfied by generating results that fail within respective predetermined criteria, and that the sensor is not functioning normally if less than 3 of said first through sixth tests are satisfied by generating results that fall within respective predetermined criteria, wherein the microprocessor determines that the third test is satisfied if the current value of impedance is less than the post-initialization value of impedance at 1 kHz, wherein the microprocessor determines that the fourth test is satisfied if the value of impedance is less than 300 kOhms at 0.1 Hz during post-initialization sensor operation, and wherein the microprocessor determines that the sixth test is satisfied if the value of real impedance is determined to be globally decreasing over successive EIS runs; and (d) based on said determination that the sensor is not functioning normally, sending an alert to a user of the sensor, by the microprocessor, that the sensor should be replaced. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of performing real-time sensor diagnostics on a subcutaneous or implanted sensor of a sensor system, said sensor including at least one working electrode and said sensor system including a microprocessor that is operatively connected to said sensor, the method comprising:
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(a) periodically performing an electrochemical impedance spectroscopy (EIS) procedure to generate multiple sets of impedance-related data for said at least one working electrode; (b) calculating, by said microprocessor, respective values of a plurality of impedance-related parameters based on said multiple sets of impedance-related data, said plurality of parameters including impedance, phase angle, and Nyquist slope; (c) based on said respective values, determining, by said microprocessor, whether the sensor is functioning normally, wherein the microprocessor; (i) performs a first test based on values of real impedance or phase angle; (ii) performs a second test based on values of sensor current (Isig) and impedance magnitude at 1 kHz; (iii) performs a third test based on a global change in the value of Nyquist slope between 0.1 Hz and 1 Hz; (iv) performs a fourth test based on the values of phase angle and impedance magnitude at 0.1 Hz; (v) performs a fifth test based on values of impedance magnitude and isig; (vi) performs a sixth test based on values of Isig, phase angle, and imaginary impedance; (vii) performs a seventh test based on values of Isig and imaginary impedance at 0.1 Hz; (viii) determines that the sensor is functioning normally if at least 4 of said first through seventh tests are satisfied by generating results that fall within respective predetermined criteria, and that the sensor is not functioning normally if less than 4 of said first through seventh tests are satisfied by generating results that fall within respective predetermined criteria, wherein the microprocessor determines that the third test is satisfied if the value of Nyquist slope is determined to be globally increasing from 0.1 Hz to 1 Hz, wherein the microprocessor determines that the fifth test is satisfied if the percentage change in the value of impedance magnitude at 1 kHz is less than or equal to 30%, or if the percentage change in the Isig is less than or equal to 30% between a first EIS run and a second EIS run, wherein the microprocessor determines that the sixth test is satisfied if at least two out of the following three criteria axe met;
(a) Isig is greater than or equal to 10 nA;
(b) the value of imaginary impedance at 1 kHz is greater than or equal to −
1500 Ohm; and
(c) the phase angle at 1 kHz is greater than or equal to −
15°
, andwherein the microprocessor determines that the seventh test is satisfied if, at 0.1 Hz, the magnitude of the difference between the value of a first ratio of the imaginary impedance to the Isig from a first run and the value of a second ratio of the imaginary impedance to the Isig from a second EIS run is less than or equal to 30% of the value of said ratio from the first EIS run; and (d) based on said determination that the sensor is not functioning normally, sending an alert to a user of the sensor, by the microprocessor, that the sensor should be replaced. - View Dependent Claims (9, 10, 11, 12, 13)
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Specification