Electrospray emitter for microfluidic channel

• US 7,081,622 B2
• Filed: 03/17/2005
• Issued: 07/25/2006
• Est. Priority Date: 03/21/2002
• Status: Expired due to Term

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: Craighead, Harold G., Kameoka, Jun
• Primary Examiner(s): Wells, Nikita
• Application Number:
  US11/082,329
• Publication Number:
  US 20050178960A1
• Time in Patent Office: 495 Days
• Field of Search: None
• US Class Current: 250/288
• CPC Class Codes: G01N 30/6095 Micromachined or nanomachined, e.g. micro- or nanosize
• CPC Class Codes: G01N 30/7266 by electric field, e.g. electrospray
• CPC Class Codes: H01J 49/0018 Microminiaturised spectrometers, e.g. chip-integrated devices, Micro-Electro-Mechanical Systems [MEMS]
• CPC Class Codes: H01J 49/165 Electrospray ionisation

Abstract

An electrospray ionization device incorporates a shaped thin film with a microfluidic channel. The device may be interfaced to a time-of-flight mass spectrometer (TFOMS). In one embodiment, the shaped thin film has a polygonal-shaped or triangle-shaped thin polymer tip formed by lithography and etching. The microfluidic channel is approximately 20 micrometer wide and 10 micrometers deep, and embossed in a substrate using a silicon master. The shaped thin film is aligned with the channel and bonded between the channel substrate and a flat plate to create a microfluidic channel with a wicking tip protruding from the end of the channel. Application of a high voltage at one end of the channel creates an electrospray from the tip, which is provided to the TFOMS.

Claims

1. An electrospray device comprising:

a wicking emitter for coupling to a fluid source, wherein the wicking emitter has an apex shaped to facilitate formation of a Taylor cone from fluid delivered to the wicking emitter.

2. The electrospray device of claim 1 wherein the apex is curved.

3. The electrospray device of claim 2 wherein the apex has a desired radius of curvature.

4. The electrospray device of claim 1, wherein the wicking emitter apex has an apex angle of between 40 and 140 degrees.

5. The electrospray device of claim 1, wherein the wicking emitter is formed with a substantially triangular shape and a curved tip.

6. The electrospray device of claim 1, wherein the wicking emitter is a substantially planar thin film.

7. The electrospray device of claim 6, wherein the wicking emitter is integrally formed as a single piece with a microfluidic device layer.

8. The electrospray emitter of claim 7 wherein the emitter is formed with a material compatible with microfabrication techniques.

9. The electrospray emitter of claim 1 wherein the emitter is formed to guide fluid to the apex of the emitter without the use of microstructure channels.

10. An electrospray emitter for directing a fluid to be ionized from a microfluidic device to a mass spectrometry apparatus, the electrospray emitter comprising:

a substantially planar emitter extending away from a surface of the microfluidic device and positioned substantially adjacent to a fluid exit, wherein the emitter is formed with an external surface to guide formation of a Taylor cone with the ionized fluid emanating from the fluid exit which moves along at least a portion of the emitter towards the mass spectrometry apparatus.

11. The electrospray emitter of claim 10, wherein the emitter is coupled to the microfluidic device and sandwiched in between a cover layer and a substrate layer.

12. The electrospray emitter of claim 10, wherein the emitter is integrally formed as a single piece with a selected microfluidic device layer.

13. The electrospray emitter of claim 10, wherein the microfluidic device is a microfabricated chip.

14. The electrospray emitter as recited in claim 10, wherein the emitter is formed with a material compatible with microfabrication techniques and formed with a polygonal geometry.

15. A method for electrospray ionization of a liquid for mass spectrometric analysis comprising:

providing a microfluidic device formed with a channel exit for releasing the liquid undergoing mass spectrometric analysis;

selecting an emitter formed with an apex that is conducive to formation of a Taylor cone derived from the liquid from the channel exit, wherein the emitter is coupled to the microfluidic device to guide the liquid by wicking along a non-enclosed surface of the emitter to a defined location; and

applying an electrical potential to the liquid sufficient to enable the formation of a Taylor cone on the emitter.

16. The method of claim 15, further comprising:

a reservoir in fluid communication with the channel exit, and wherein the reservoir is operatively connected to a power supply; and

a counter electrode positioned at the defined location wherein a voltage can be applied across the power supply and counter electrode sufficient to form the Taylor cone and achieve electrospray ionization.

17. The method of claim 15, further comprising:

a mass spectrometer with an orifice positioned relative to the Taylor cone and spaced from the emitter to receive at least a portion of the electrospray.

18. The method of claim 17, wherein the orifice of the mass spectrometer is positioned substantially in-line with the Taylor cone.

19. The method of claim 17, wherein the orifice of the mass spectrometer is positioned off-axis relative to the Taylor cone.

20. The electrospray device of claim 15, wherein the emitter is a substantially planar thin polygonal shaped film having an apex that is conducive to formation of a Taylor cone derived from the liquid from the channel exit.