Tear fluid conductivity sensor

• US 9,572,522 B2
• Filed: 12/20/2013
• Issued: 02/21/2017
• Est. Priority Date: 12/20/2013
• Status: Active Grant

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: Verily Life Sciences LLC (Alphabet Inc.)
• Inventors: Liu, Zenghe, Yao, Huanfen
• Primary Examiner(s): Natnithithadha, Navin
• Assistant Examiner(s): MESSERSMITH, ERIC J
• Application Number:
  US14/136,895
• Publication Number:
  US 20150173658A1
• Time in Patent Office: 1,159 Days
• US Class Current: 1/1
• CPC Class Codes: A61B 2560/0219 of externally powered implanted units
• CPC Class Codes: A61B 2562/028 Microscale sensors, e.g. electromechanical sensors [MEMS]
• CPC Class Codes: A61B 2562/12 Manufacturing methods specially adapted for producing sensors for in-vivo measurements
• CPC Class Codes: A61B 3/101 for examining the tear film
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• 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 5/1468 using chemical or electrochemical methods, e.g. by polarographic means A61B5/1486 takes precedence
• CPC Class Codes: A61B 5/6821 Eye

Abstract

Disclosed herein is a fluid conductivity sensor that can be used to obtain in-vivo measurements of conductivity of biological fluid samples, for example, to determine osmolarity. The conductivity sensor can be disposed on a substrate that is at least partially embedded within a polymeric material of a body-mountable device. The conductivity sensor can include a frame having a trench formed therein that defines a fluid sample cell. First and second electrodes can be formed on sidewalls of the trench, such that the first and second electrodes are on opposite sides of the fluid sample cell. A controller in the body-mountable device can operate the sensor by applying a voltage to the electrodes and measuring a current through a fluid occupying the fluid sample cell. The body-mountable device may indicate the current measurements wirelessly using an antenna.

Claims

1. An eye-mountable device comprising:

a transparent polymeric material;

a substrate at least partially embedded within the polymeric material;

an antenna disposed on the substrate;

a conductivity sensor disposed on the substrate, wherein the conductivity sensor includes;

a frame having a trench formed therein that defines a fluid sample cell, wherein the trench includes a first sidewall and a second sidewall,

a first electrode formed on the first sidewall, and

a second electrode formed on the second sidewall such that the first and second electrodes are on opposite sides of the fluid sample cell; and

a controller electrically connected to the sensor electrodes and the antenna, wherein the controller is configured to;

(i) apply a voltage to the electrodes sufficient to generate a current through the electrodes related to a conductance of a fluid occupying the fluid sample cell;

(ii) measure the generated current; and

(iii) use the antenna to indicate the measured current.

2. The eye-mountable device of claim 1, wherein the first electrode and the second electrode are separated by a substantially constant separation distance throughout the fluid sample cell.

3. The eye-mountable device of claim 2, wherein the separation distance between the two electrodes is less than about 100 micrometers.

4. The eye-mountable device of claim 1, wherein the transparent polymeric material has a concave surface and a convex surface, and 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.

5. The eye-mountable device of claim 4,

wherein the first and second electrodes each include a width dimension and a length dimension;

wherein the width dimension of each electrode extends along a depth of the fluid sample cell, which depth is oriented approximately perpendicular to a locally proximate region of the convex surface of the polymeric material; and

wherein the length dimension of each electrode extends within a plane approximately co-planar with the locally proximate region of the convex surface.

6. The eye-mountable device of claim 4,

wherein the two electrodes each substantially span a depth of the fluid sample cell that extends transverse to a locally proximate region of the convex surface of the polymeric material;

and

wherein the depth of the fluid sample cell is greater than about 20 micrometers.

7. The eye-mountable device of claim 6, wherein the depth of the fluid sample cell is between about 50 micrometers and about 100 micrometers.

8. The eye-mountable device of claim 4, wherein the polymeric material includes a channel situated so as to expose the electrodes to tear fluid, via the channel, when the concave surface is mounted over an eye.

9. The eye-mountable device of claim 4, wherein the polymeric material includes an electrolyte-absorbant silicon hydrogel in the vicinity of the electrodes so as to expose the electrodes to electrolytes in tear fluid, via diffusion through the silicon hydrogel, when the concave surface is mounted over an eye.

10. The eye-mountable device of claim 1, wherein the fluid sample cell has a volume less than about 100 nano liters.

11. The eye-mountable device of claim 1, wherein the voltage applied to the sensor electrodes is a periodically varying AC voltage which causes the generated current to be an AC current, and wherein the controller is further configured to generate the AC voltage and to measure the AC current.

12. The eye-mountable device of claim 1, wherein the frame of the conductivity sensor includes a silicon wafer.

13. The eye-mountable device of claim 1, wherein the transparent polymeric material includes a silicone elastomer.

14. The eye-mountable device of claim 1, further comprising an energy harvesting system that captures electrical energy from incident radiation to power the controller.