Standby Biasing Of Electrochemical Sensor To Reduce Sensor Stabilization Time During Measurement

• US 20140209481A1
• Filed: 01/25/2013
• Published: 07/31/2014
• Est. Priority Date: 01/25/2013
• Status: Abandoned Application

• Current Assignee: Verily Life Sciences LLC (Alphabet Inc.)
• Original Assignee: Google Inc. (Alphabet Inc.)
• Inventors: Pletcher, Nathan, Otis, Brian
• Application Number:
  US13/750,493
• Publication Number:
  US 20140209481A1
• Time in Patent Office: Days
• US Class Current: 205/777.5
• CPC Class Codes: A61B 2560/0209 adapted for power saving
• CPC Class Codes: A61B 2560/0214 of power generation or supply
• CPC Class Codes: A61B 2560/0219 of externally powered implanted units
• CPC Class Codes: A61B 5/0004 characterised by the type of physiological signal transmitted
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/14507 specially adapted for measuring characteristics of body fluids other than blood devices for taking samples of body liquids A61B10/0045
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: A61B 5/1486 using enzyme electrodes, e.g. with immobilised oxidase
• CPC Class Codes: A61B 5/14865 invasive, e.g. introduced into the body by a catheter or needle or using implanted sensors
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/6821 Eye
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence
• CPC Class Codes: G01N 27/3271 Amperometric enzyme electrodes for analytes in body fluids, e.g. glucose in blood amperometry per se G01N27/49; aspects concerning the enzyme reagent C12Q1/001

Abstract

An eye-mountable device includes an electrochemical sensor embedded in a polymeric material configured for mounting to a surface of an eye. The electrochemical sensor applies a stabilization voltage between a working electrode and a reference electrode to allow the amperometric current to stabilize before powering measurement electronics configured to measure the amperometric current and communicate the measured amperometric current. The electrochemical sensor consumes less power while applying the stabilization voltage than during the measurement. The measurement is initiated in response to receiving a measurement signal at an antenna in the eye-mountable device.

Claims

1. A method comprising:

applying a stabilization voltage between a working electrode and a reference electrode in an eye-mountable device, wherein the stabilization voltage is sufficient to cause an analyte to undergo an electrochemical reaction at the working electrode;

while the stabilization voltage is being applied, wirelessly receiving a measurement signal at an antenna in the eye-mountable device;

responsive to receiving the measurement signal, activating measurement electronics in the eye-mountable device to transition the measurement electronics from a standby mode to an active mode, wherein the measurement electronics consume more power in the active mode than in the standby mode; and

during the active mode, operating the measurement electronics to (i) measure an amperometric current through the working electrode, wherein the amperometric current is related to the analyte, and (ii) wirelessly communicate the measured amperometric current via the antenna.

2. The method according to claim 1, further comprising:

after wirelessly communicating the measured amperometric current via the antenna, de-activating the measurement electronics to transition the measurement electronics from the active mode to the standby mode.

3. The method according to claim 1, further comprising intermittently activating the measurement electronics to wirelessly communicate a series of amperometric current values measured through the working electrode, wherein each of the amperometric current values is measured following a stabilization period during which the stabilization voltage is applied to allow current through the working electrode caused by the stabilization voltage to reach a stable value prior to measurement.

4. The method according to claim 3, wherein the measurement electronics are intermittently activated with a duty cycle of less than 10 percent.

5. The method according to claim 1, further comprising:

during the active mode, applying a measurement voltage between the working electrode and the reference electrode, wherein the measurement voltage generates the amperometric current.

6. The method according to claim 5, wherein the stabilization voltage is supplied by an auxiliary power supply and the measurement voltage is supplied by a primary power supply.

7. The method according to claim 5, wherein the stabilization voltage and the measurement voltage are approximately equal.

8. The method according to claim 5, wherein the stabilization voltage is within 20 percent of the measurement voltage.

9. The method according to claim 1, further comprising:

during the active mode, harvesting energy from radio frequency (RF) radiation received at the antenna to power the measurement electronics.

10. The method according to claim 1, further comprising:

applying the stabilization voltage during a stabilization period, wherein the stabilization period has a duration sufficient to allow current through the working electrode to reach a stable value prior to activating the control electronics such that the amperometric current measured by the measurement electronics is not affected by transient variations.

11. The method according to claim 1, wherein the received measurement signal includes radio frequency radiation for powering an energy harvesting power supply, and wherein the method further comprises:

rectifying electrical signals on the antenna caused by the received radio frequency radiation to thereby generate a supply voltage; and

applying the generated supply voltage to the measurement electronics to power the measurement electronics.

12. The method according to claim 1, further comprising:

prior to receiving a subsequent measurement signal, validating the measured amperometric current by operating the measurement electronics in the active mode to measure a second amperometric current value through the working electrode and wirelessly communicate the second amperometric current value via the antenna.

13. A method comprising:

during a stabilization period, wirelessly transmitting, by a reader, a stabilization signal to an eye-mountable device comprising a working electrode, stabilization electronics, measurement electronics, and an antenna, wherein the stabilization signal is configured to cause the stabilization electronics to apply a stabilization voltage between the working electrode and the reference electrode, wherein the stabilization voltage is sufficient to cause an analyte to undergo an electrochemical reaction at the working electrode;

during a measurement period following the stabilization period, wirelessly transmitting, by the reader, a measurement signal to the eye-mountable device, wherein the measurement signal is configured to (i) cause the measurement electronics to measure an amperometric current through the working electrode, wherein the amperometric current is related to the analyte, (ii) cause the measurement electronics to wirelessly communicate the measured amperometric current via the antenna, and (iii) supply power for powering the measurement electronics; and

receiving, by the reader, an indication of the measured amperometric current wirelessly communicated from the eye-mountable device.

14. The method according to claim 13, further comprising:

during an idle period following the measurement period, the reader discontinuing transmission of wireless signals to the eye-mountable device.

15. The method according to claim 13, further comprising:

obtaining, by the reader, a series of amperometric current values wirelessly communicated from the eye-mountable device, by;

transmitting a stabilization signal to the eye-mountable device to cause the stabilization electronics to apply the stabilization voltage between the working electrode and the reference electrode;

transmitting a measurement signal to the sensing platform to cause the measurement electronics to measure an amperometric current through the working electrode and wirelessly communicate the measured amperometric current; and

receiving an indication of the measured amperometric current; and

wherein each transmission of the measurement signal immediately follows a transmission of the stabilization signal such that each of the series of amperometric current values is measured following a stabilization period during which the stabilization voltage is applied between the working electrode and the reference electrode to allow current through the working electrode caused by the stabilization voltage to reach a stable value prior to measurement.

16. The method according to claim 15, wherein the measurement signal is transmitted with a duty cycle of less than 10 percent.

17. The method according to claim 13, further comprising:

receiving, by the reader, an indication of a second measured amperometric current obtained during the measurement period;

comparing the values of the two measured amperometric currents; and

determining, based on the comparison, if the current through the working electrode of the electrochemical sensor reached a stable value prior to the measurement period.

18. An eye-mountable device comprising:

a transparent polymeric material having a concave surface and a convex surface, wherein the concave surface is configured to be removably mounted over a corneal surface and the convex surface is configured to be compatible with eyelid motion when the concave surface is so mounted;

an antenna;

an electrochemical sensor that includes a working electrode and a reference electrode;

stabilization electronics operable to apply a stabilization voltage between the working electrode and the reference electrode, wherein the stabilization voltage is sufficient to cause an analyte to undergo an electrochemical reaction at the working electrode;

measurement electronics, wherein the measurement electronics, when activated, are configured to;

(i) apply a measurement voltage between the working electrode and the reference electrode, (ii) measure an amperometric current through the working electrode, wherein the amperometric current is related to the analyte, and (iii) use the antenna to communicate the measured amperometric current; and

a controller, wherein the controller is configured to operate the stabilization electronics to apply the stabilization voltage during a stabilization period and to activate the measurement electronics during a measurement period in response to receiving a measurement signal via the antenna.

19. The device according to claim 18, wherein the controller is further configured to de-activate the measurement electronics during the stabilization period.

20. The device according to claim 18, further comprising a power supply configured to harvest radiation incident on the antenna to power the measurement electronics during the measurement period.

21. The device according to claim 20, wherein the power supply includes a rectifier configured to harvest energy from electrical signals on the antenna caused by incident radio frequency radiation.

22. The device according to claim 20, further comprising an auxiliary power supply configured to power the stabilization electronics during the stabilization period.

23. The device according to claim 22, wherein the auxiliary power supply includes a photovoltaic cell configured to harvest energy from incident light.