Method for chemical sensing using a microfabricated teeter-totter resonator

• US 6,823,720 B1
• Filed: 05/12/2003
• Issued: 11/30/2004
• Est. Priority Date: 05/12/2003
• Status: Active Grant

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Adkins, Douglas Ray, Shul, Randy J., Heller, Edwin J.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Saint-Surin, Jacques M.
• Application Number:
  US10/436,596
• Time in Patent Office: 568 Days
• Field of Search: 73/542.5, 73/544.1, 73/645.3, 73/617.9, 73/240.1, 73/240.6, 735/79
• US Class Current: 73/54.25
• CPC Class Codes: G01N 11/16 by measuring damping effect upon oscillatory body
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 2291/0421 Longitudinal waves
• CPC Class Codes: G01N 29/022 Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices microdevices per se B81B
• CPC Class Codes: G01N 29/036 by measuring frequency or resonance of acoustic waves
• CPC Class Codes: G01N 29/222 Constructional or flow details for analysing fluids optoacoustic fluid cells G01N29/2425

Abstract

A method for sensing a chemical analyte in a fluid stream comprises providing a microfabricated teeter-totter resonator that relies upon a Lorentz force to cause oscillation in a paddle, applying a static magnetic field substantially aligned in-plane with the paddle, energizing a current conductor line on a surface of the paddle with an alternating electrical current to generate the Lorentz force, exposing the resonator to the analyte, and detecting the response of the oscillatory motion of the paddle to the chemical analyte. Preferably, a chemically sensitive coating is disposed on at least one surface of the paddle to enhance the sorption of the analyte by the paddle. The concentration of the analyte in a fluid stream can be determined by measuring the change in the resonant frequency or phase of the teeter-totter resonator as the chemical analyte is added to or removed from the paddle.

Claims

1. A method for sensing a chemical analyte in a fluid stream, comprising:

providing a microfabricated teeter-totter resonator, the resonator comprising;

a frame,

a paddle having a first end and a second end and wherein the paddle is pivotably anchored to the frame by pivot arms at each end of the paddle, the pivot arms defining an axis of rotation of the paddle,

a current conductor line on a surface of the paddle that is displaced from the axis of rotation of the paddle,

means for applying a static magnetic field aligned substantially in-plane with the paddle and substantially perpendicular to the current conductor line and the axis of rotation, and

means for energizing the current conductor line with an alternating electrical current; and

applying the static magnetic field;

energizing the current conductor line with the alternating electrical current to excite an oscillatory motion of the paddle about the axis of rotation;

exposing the resonator to the chemical analyte in the fluid stream; and

detecting the response of the oscillatory motion of the paddle to the chemical analyte.

2. The method of claim 1, wherein the resonator further comprises a chemically sensitive coating disposed on at least one surface of the paddle for sorbing the chemical analyte from the fluid stream.

3. The method of claim 2, wherein the chemically sensitive coating comprises a polymer or getter.

4. The method of claim 1, further comprising collecting the chemical analyte on the paddle.

5. The method of claim 1, wherein the detecting comprises measuring the impedance of the current conductor line.

6. The method of claim 1, wherein the detecting comprises measuring the rotational displacement of the oscillatory motion of the paddle.

7. The method of claim 1, wherein the detecting comprises measuring the phase of the current relative to the voltage of the current conductor line.

8. The method of claim 1, wherein the detecting comprises measuring the phase of the current relative to the rotational displacement of the oscillatory motion.

9. The method of claim 1, wherein the resonator further comprises a second current conductor line on a surface of the paddle that is displaced from the axis of rotation of the paddle for detecting the oscillatory motion excited by the energizing of the current conductor line with the alternating electrical current.

10. The method of claim 9, wherein the detecting comprises measuring the output voltage induced in the second current conductor line.

11. The method of claim 1, wherein the current conductor line substantially follows the periphery of the paddle.

12. The method of claim 1, wherein the paddle comprises a rectangular shape.

13. The method of claim 1, wherein the frame comprises silicon.

14. The method of claim 1, wherein the paddle comprises silicon, polysilicon, silicon nitride, silicon dioxide, or a polymer.

15. The method of claim 1, wherein the energizing of the current conductor line with the alternating electrical current excites the oscillatory motion of the paddle in a resonant mode.

16. The method of claim 1, wherein the resonator further comprises a second paddle having a first end and a second end, and wherein the second paddle is pivotably anchored to the frame by pivot arms at each end of the second paddle, and wherein that the pivot arms of the second paddle are on the axis of rotation of the paddle and the current conductor line is further on a surface of the second paddle that is displaced from the axis of rotation to excite an oscillatory motion of the second paddle about the axis of rotation when the current conductor line is energized with the alternating electrical current.

17. The method of claim 16, wherein the current conductor line is disposed on the surface of the second paddle such that the oscillatory motion of the second paddle is counter-rotating to the oscillatory motion of the paddle.

18. The method of claim 16, wherein the current conductor line of the paddle and the second paddle is configured in a bridge circuit.

19. The method of claim 16, wherein a chemically sensitive coating is disposed on at least one surface of the second paddle for sorbing the chemical analyte from the fluid stream.

20. The method of claim 19, wherein the chemically sensitive coating comprises a polymer or getter.