Microfabrication of a microdialysis probe with nanoporous membrane

Patent metadata

Field	Value
Publication number	US-11014047-B2
Application number	US-201615764124-A
Country	US
Kind code	B2
Filing date	Nov 29, 2016
Priority date	Dec 8, 2015
Publication date	May 25, 2021
Grant date	May 25, 2021

Abstract

Microdialysis sampling is an essential tool for in vivo neuro-chemical monitoring. Conventional dialysis probes are over 220 μm in diameter and have limited flexibility in design because they are made by assembly using preformed membranes. The probe size constrains spatial resolution and governs the amount of tissue damaged caused by probe insertion. To overcome these limitations, we have developed a method to microfabricate probes in Si that are 45 μm thick 180 μm wide. The probes contain a buried, U-shaped channel that is 30 μm deep 60 μm wide and terminates in ports for external connection. A 4 mm length of the probe is covered with a 5 μm thick nanoporous membrane. The membrane was microfabricated by deep reactive ion etching through a porous aluminum oxide layer. The microfabricated probe has cross-sectional area that is 79% less than that of the smallest conventional microdialysis probes. The probes yield 2-7% relative recovery at 100 nL/min perfusion rate for a variety of small molecules. The probe was successfully tested in vivo by sampling from the striatum of live rats. Fractions were collected at 20 min intervals (2 μL) before and after an injection of 5 mg/kg, i.p amphetamine. Analysis of fractions by liquid chromatography-mass spectrometry revealed reliable detection of 13 neurochemicals, including dopamine and acetylcholine, at basal conditions. Amphetamine evoked a 43-fold rise in dopamine, a result nearly identical to a conventional dialysis probe in the same animal. The microfabricated probes have potential for sampling with higher spatial resolution and less tissue disruption than conventional probes. It may also be possible to add functionality to the probes by integrating other components, such as electrodes, optics, and additional channels.

First claim

What is claimed is:

1. A microfabricated microdialysis probe made of a unitary block and comprising, from proximal to distal end, a body, a support shank, a shank, and a tip, wherein the body comprises an inlet port and an outlet port;
the probe further comprising a single channel in the surface of the probe and running from the inlet port to the shank, through the body, through the support shank, and through the shank to the tip and back to the outlet port, the inlet port and the outlet port both being on the proximal end,
wherein a porous layer covers the channel in at least part of the shank and a solid layer covers the channel everywhere the porous layer does not, wherein the porous layer has a plurality of pores having a diameter in the range of 50 nm to 100 nm.

2. The probe according to claim 1 , wherein the channel path is straight with a U-shape turn at the tip.

3. The probe according to claim 1 , wherein the tip is pointed to facilitate entry of the probe into a tissue.

4. The probe according to claim 1 , wherein the overall length of the probe is 2 to 11 mm.

5. The probe according to claim 1 , wherein the thickness of the shank is 10 to 40 microns and the other parts have the same thickness as or a greater thickness than the shank.

6. The probe according to claim 5 , wherein the width of the shank is 30 to 180 microns.

7. The probe according to claim 1 , wherein the depth of the channel is 5 to 35 microns and the width of the channel is 5 to 65 microns.

8. The probe according to claim 1 , wherein the solid layer comprises polysilicon.

9. The probe according to claim 1 , wherein the porous layer comprises anodized aluminum oxide.

10. The probe according to claim 1 , wherein the porous layer comprises a polysilicon layer and a layer of anodized aluminum oxide, wherein the polysilicon layer covers the channel and is in contact with the unitary block and the anodized aluminum oxide layer is disposed on top of the polysilicon.

11. The probe according to claim 1 , wherein the porous layer has a thickness of 1 to 10 microns.

12. The probe according to claim 1 , wherein the porous layer covers a 0.1 to 8 mm length of the shank, including over a portion of the channel.

13. The probe according to claim 1 , wherein the unitary block is made of silicon.

14. The probe according to claim 1 , wherein the porous layer is characterized by a pore density of 8±2×10 13 per square meter.

15. The probe according to claim 1 , wherein the porous layer is characterized by a porosity of 16 to 70 percent, where the porosity is defined as the ratio of the area of the pores to the area of the membrane.

16. A method of identifying molecules in a fluid, comprising inserting the tip and at least a part of the shank of the probe according to claim 1 into the fluid, flowing a solution from the inlet port through the channel and back to the outlet port while the probe is inserted, collecting a fraction or fractions of the solution as it emerges from the outlet port, and analyzing the collected fraction or fractions for the presence of the molecule.

17. The method according to claim 16 , wherein the solution and the fluid are isotonic.

18. The method according to claim 16 , wherein the porous layer is characterized by a pore density of 8±2×10 13 per square meter.

19. The method according to claim 16 , wherein the porous layer is characterized by a porosity of 16 to 70 percent, where the porosity is defined as the ratio of the area of the pores to the area of the membrane.

20. A method for delivering molecules into a fluid, comprising inserting the tip and at least a part of the shank covered by the porous membrane of the probe according to claim 1 into the fluid, flowing a solution from the inlet port through the channel and back to the outlet port while the probe is inserted, wherein the solution has a higher concentration of the molecule than the fluid and the molecules pass by dialysis from the solution through the membrane into the fluid.

21. The method according to claim 20 , wherein the solution and the fluid are isotonic.

22. The method according to claim 20 , wherein the porous layer is characterized by a pore density of 8±2×10 13 per square meter.

23. The method according to claim 20 , wherein the porous layer is characterized by a porosity of 16 to 70 percent, where the porosity is defined as the ratio of the area of the pores to the area of the membrane.

24. A method for forming a dialysis membrane over the single channel in the microfabricated microdialysis probe of claim 1 , comprising:
forming a polysilicon layer over the single channel;
depositing a layer of aluminum over the polysilicon layer;
anodizing the aluminum layer to make a layer of porous anodized aluminum oxide that is a mask on top of the underlying polysilicon layer;
forming holes in the polysilicon layer by deep reactive ion etching through the porous anodized aluminum oxide mask to make the dialysis membrane covering the single channel.

25. The method of claim 24 , wherein the single channel is formed at the surface of a silicon body.

26. The method of claim 24 , further comprising removing the porous anodized aluminum oxide mask, depositing a fresh layer of aluminum, and anodizing the fresh aluminum layer to provide a fresh layer of porous anodized aluminum oxide.

27. The method of claim 26 , wherein the fresh layer of aluminum and the fresh layer of porous anodized aluminum oxide has a thickness greater than the thickness of the porous anodized aluminum oxide mask.

Assignees

• Univ Michigan Regents

Inventors

• Kennedy Robert T
• Yoon Hyeun Joong
• Ngernsutivorakul Thitaphat
• Lee Woong Hee

Classifications

• B01D71/0213

  Silicon · CPC title

• B01D67/0065

  by anodic oxidation · CPC title

• B01D61/243 Primary

  Dialysis · CPC title

• C25D11/045

  for forming AAO templates · CPC title

• B01D61/025

  Reverse osmosis; Hyperfiltration · CPC title