Chemical sensor system

• US 20010016683A1
• Filed: 12/20/2000
• Published: 08/23/2001
• Est. Priority Date: 10/05/1998
• Status: Active Grant

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Abraham P. Lee, Amy W. Wang, Christopher B. Darrow, Joe H. Satcher Jr, Stephen M. Lane
• Inventors: Satcher, Joe H. Jr., Wang, Amy W., Darrow, Christopher B, Lee, Abraham P., Lane, Stephen M.
• Granted Patent: US 6,480,730 B2
• Time in Patent Office: Days
• US Class Current: 600/347
• CPC Class Codes: A61B 2562/028 Microscale sensors, e.g. electromechanical sensors [MEMS]
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement

Abstract

An implantable chemical sensor system for medical applications is described which permits selective recognition of an analyte using an expandable biocompatible sensor, such as a polymer, that undergoes a dimensional change in the presence of the analyte. The expandable polymer is incorporated into an electronic circuit component that changes its properties (e.g., frequency) when the polymer changes dimension. As the circuit changes its characteristics, an external interrogator transmits a signal transdermally to the transducer, and the concentration of the analyte is determined from the measured changes in the circuit. This invention may be used for minimally invasive monitoring of blood glucose levels in diabetic patients.

Claims

1. An implantable chemical sensor system for measuring the concentration of an analyte of interest, comprising:

a sensor, comprising a material that selectively responds to an analyte of interest by changing its dimensions;

an implantable transducer, comprising an electronic circuit having at least one variable electrical characteristic that changes in response to dimensional changes of the sensor; and

a telemetry device that interrogates the transducer transdermally to measure the changes in the electrical characteristic of the circuit as the concentration of analyte changes.

2. The sensor system as recited in

claim 1

, wherein the circuit comprises at least one mechanically actuated circuit component, wherein the dimensional changes of the sensor are used to mechanically actuate changes in the circuit component.

3. The sensor system as recited in

claim 2

, wherein the circuit component comprises a variable capacitor.

4. The sensor system as recited in

claim 3

, wherein the capacitor comprises two plates, wherein at least one plate moves relative to the other in response to the sensor changing its dimensions.

5. The sensor system as recited in

claim 4

, wherein the transducer further comprises an area that moves in response to the sensor changing dimensions and that is connected to at least one plate.

6. The sensor system as recited in

claim 1

, wherein the transducer further comprises a housing for the sensor, including an area that moves in response to the sensor changing dimensions, and including a rigid, analyte-permeable material that constrains the sensor in the housing.

7. The sensor system as recited in

claim 6

, wherein the area that moves is a pleated, expansible area.

8. The sensor system as recited in

claim 3

, wherein the capacitor comprises two fixed plates and a movable dielectric, wherein changes in dimensions of the sensor cause relative motion of the dielectric and the plates, whereby the capacitance of the capacitor changes.

9. The sensor system as recited in

claim 2

, wherein the circuit component comprises a variable inductor.

10. The sensor system as recited in

claim 9

, wherein the inductor comprises an inductance coil, and the coil'"'"'s inductance changes in response to the sensor changing its dimensions.

11. The sensor system as recited in

claim 10

, further comprising a magnetic material that moves in response to the sensor changing its dimensions.

12. The sensor system as recited in

claim 9

, wherein the inductor comprises an inductance coil and a magnetic material, wherein at least one of the coil and magnetic material move relative to the other, and the coil'"'"'s inductance changes in response to the sensor changing its dimensions.

13. The sensor system as recited in

claim 1

, wherein the sensor comprises a polymer capable of reversibly expanding and contracting in volume in the presence of the analyte.

14. The sensor system as recited in

claim 1

, wherein the sensor comprises a hydrogel that changes dimensions in the presence of glucose.

15. The sensor system as recited in

claim 1

, wherein the sensor responds to at least one analyte selected from the group consisting of sugars, urea, ammonia, hydrogen ions, alkaline earth ions, alkali metal ions, transition metal ions, enzymes, and narcotic substances.

16. The sensor system as recited in

claim 2

, wherein the circuit component comprises a micro electromechanical system (MEMS) device.

17. The sensor system as recited in

claim 16

, wherein the MEMS device comprises a cavity into which the sensor is situated, and a flexible conductive membrane covering a portion of the cavity such that the membrane moves in response to the sensor changing its dimensions.

18. The sensor system as recited in

claim 17

, wherein the transducer includes a planar conductive material, wherein the planar material and the membrane comprise plates of a capacitor, wherein the capacitor'"'"'s capacitance changes in response to the sensor changing its dimensions.

19. The sensor system as recited in

claim 18

, wherein the planar conductive material is deposited on a surface of an etchable substrate.

20. The sensor system as recited in

claim 19

, wherein a well is formed on the surface of the substrate, and the conductive material is deposited thereon.

21. The sensor system as recited in

claim 17

, wherein the MEMS device comprises at least one variable circuit component comprising a variable capacitor, the capacitance of which varies in response to deflections of the membrane.

22. The sensor system as recited in

claim 21

, wherein the MEMS device further comprises an integrated inductor.

23. The sensor system as recited in

claim 17

, wherein the MEMS device comprises at least one variable circuit component comprising a variable inductor, wherein the inductor comprises an inductor coil and a magnetic material that moves with the membrane.

24. The sensor system as recited in

claim 1

, wherein the circuit comprises a micro electromechanical system (MEMS) device which further comprises at least one variable circuit component co-fabricated with other circuit elements to form an integrated MEMS assembly.

25. The sensor system as recited in

claim 1

, wherein telemetry device measures the resonant frequency of the transducer circuit.

26. The sensor system as recited in

claim 1

, wherein telemetry device measures an acoustic tone, the frequency of which is moderated by the transducer circuit.

27. A method for measuring the concentration of an analyte of interest using an implantable sensor system, comprising:

providing a transducer, comprising an electronic circuit and a sensor, wherein the sensor comprises a material that selectively responds to an analyte of interest by changing its dimensions, and wherein the circuit has at least one variable electrical characteristic that changes in response to dimensional changes of the sensor;

implanting the transducer subcutaneously into a patient; and

providing a telemetry device that interrogates the transducer transdermally to measure the changes in the electrical characteristic of the circuit as the concentration of analyte changes.