Microfabricated AC impedance sensor

• US 6,437,551 B1
• Filed: 11/01/2000
• Issued: 08/20/2002
• Est. Priority Date: 11/02/1999
• Status: Expired due to Fees

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Boser, Bernhard E., Hamilton, Julie K., Ackler, Harold D., Eldredge, Adam B., Gascoyne, Peter R. C., Krulevitch, Peter, Fuller, Christopher K., Wang, Xiao-Bo, Becker, Frederick, Swierkowski, Stefan P.
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): Deb, Anjan K.
• Application Number:
  US09/704,355
• Time in Patent Office: 657 Days
• Field of Search: 324/71.4, 324/71.1, 324/609, 324/601, 324/649, 324/525, 324/693, 428/34.4, 156/99, 436/518
• US Class Current: 324/71.1
• CPC Class Codes: B01L 3/5027 by integrated microfluidic structures, i.e. dimensions of channels and chambers are such that surface tension forces are important, e.g. lab-on-a-chip B01L3/5023 takes precedence; micromixers B01F33/30; microreactors for synthesis B01J19/0093; microcapillary devices in general B81B1/00
• CPC Class Codes: G01N 2015/139 Measuring the ratio of AC/DC impedances
• CPC Class Codes: G01N 27/026 Dielectric impedance spectroscopy electrochemical impedance spectroscopy for measuring corrosion G01N17/02
• CPC Class Codes: G01N 33/5438 Electrodes

Abstract

A microfabricated instrument for detecting and identifying cells and other particles based on alternating current (AC) impedance measurements. The microfabricated AC impedance sensor includes two critical elements: 1) a microfluidic chip, preferably of glass substrates, having at least one microchannel therein and with electrodes patterned on both substrates, and 2) electrical circuits that connect to the electrodes on the microfluidic chip and detect signals associated with particles traveling down the microchannels. These circuits enable multiple AC impedance measurements of individual particles at high throughput rates with sufficient resolution to identify different particle and cell types as appropriate for environmental detection and clinical diagnostic applications.

Claims

1. A device including at least one microfabricated alternating current (AC) impedance sensor, including:

at least one microfluidic channel for the passage therethrough of particle laden sample fluid,

a first electrode located in the at least one microfluidic channel,

a second electrode located adjacent the microfluidic channel and in spaced relation to said first electrode,

an alternating current source operatively connected to said first and second electrodes, and

means for electrically connecting said first and second electrodes to an impedance measuring circuit,

whereby impedance between the first and second electrode is changed by particles or cells in the sample fluid passing through said microfluidc channel.

2. The impedance sensor of claim 1, wherein said microfluidic channel is located intermediate a pair of bonded members formed of material selected from the group consisting of glass, plastic, and non-conductive material.

3. The impedance sensor of claim 2, wherein one of said pair of bonded members includes a plurality of openings in alignment with said microfluidic channel and with said first and second electrodes, said openings functioning as a fluid inlet/outlet or as an electronic feedthrough for connecting said electrodes to said impedance measuring circuit.

4. The impedance sensor of claim 1, wherein said microfluidic channel is located within low parasitic capacitance material.

5. The impedance sensor of claim 1, wherein said first and second electrodes are composed of material selected from the group consisting of platinum and gold.

6. The impedance sensor of claim 5, wherein said first and second electrodes are composed of platinum with a chromium adhesion layer.

7. The impedance sensor of claim 6, wherein the platinum has a thickness of 0.1-0.2 microns and the chromium has a thickness of about 0.5 nm.

8. The impedance sensor of claim 1, wherein said first and second electrodes have a length of 10 μ

m to 200 μ

m and width of 10 μ

m to 200 μ

m.

9. The impedance sensor of claim 1, wherein said impedance measuring circuit comprises an integrated chip capable of measuring a plurality of frequencies simultaneously and eliminates a need for a reference channel.

10. The device of claim 9, comprising a microfluidic chip containing at least a sample input and a reference input in fluid communication with said at least two microfluidic channels, a fluid output in fluid communication with each of said microfluidic channels, three electrode contacts located adjacent said at least two microfluidic channels, and a fluid ground contact operatively connected to said sample input.

11. The device of claim 10, wherein at least said electrodes are composed of material selected from the group consisting of platinum and gold.

12. The AC sensor of claim 11, which has an operational bandwidth which approaches 10 MHz with a signal-to-noise ratio of about 40 dB.

13. The AC sensor of claim 11, includes an impedance measuring circuit constructed to measure particle impedance at three or more frequencies simultaneously, enabling derivation of multiple particle parameters.

14. The AC sensor of claim 11, including two identical microchannel sensors, one for sensing particles as they flow through a microchannel and other for use as an electrical reference.

15. The AC sensors of claim 11, wherein the two identical microchannel sensors are fabricated in a microfluidic chip mounted on a circuit board.

16. The AC sensors of claim 11, wherein the two identical microchannel sensors include a pair of microchannels, a sample input and a reference input connected to one end of each of said microchannels, a fluid output connected to opposite ends of said microchannels, three electrode contacts positioned adjacent said pair of microchannels, and a fluid ground contact electrically connected to said sample input.

17. The impedance sensor of claim 1, additionally including a reference electrode, said impedance measuring circuit being electrically connected to said reference electrode.

18. The device of claim 17, wherein adjacent of said three electrode contacts are electrically connected to electrodes located in one of the two microfluidic channels.

19. The device of claim 18, wherein at least said electrodes are constructed of platinum with a chromium adhesion layer.

20. The device of claim 1, having two identical AC impedance sensors and at least two microfluidic channels, one of said channels have a sample fluid therein, another of said channels having a reference fluid, said impedance measuring circuits containing electronics that simultaneously measure resistive and reactive changes in the differential impedance of the two sensors.

21. A microfluidc device operative connected to an impedance measuring circuit, comprising:

a pair of aligned and bonded glass members,

at least one of said glass members having a microchannel therein,

said at least one glass member having a pair of electrode pads located on a surface thereof and on opposite sides of said microchannel,

an electrode located in said microchannel and electrically connected to one of said pair of electrode pads,

another of said glass members having a plurality of openings extending therethrough, two of said openings being in alignment with said pair of electrode pads and at least one of said openings being in communication with said microchannel,

said another of said glass members having an electrode located on a surface thereof adjacent said at least one of said glass members and electrically connected to another of said pair of electrode pads, and

an alternating current source operatively connected to said electrodes,

whereby said electrodes are electrically connected to said impedance measuring circuit via said two of said openings.

22. A microfabricated flow-through impedance characterization system capable of performing AC multi-frequency measurements on cells and other particles, comprising:

an AC sensor which measures both resistive and reactive impedance of passing particles at rates of up to 100 particles per second.