Enhanced fill-factor NMR coils and associated methods
An NMR probe which includes a probe matrix ( 24 ) having a void sample ( 28 ) volume therein. A conductive coil ( 16, 26 ) can be at least partially embedded in the probe matrix ( 24 ). By embedding the conductive coil ( 16, 26 ) in the probe matrix ( 24 ), the fill-factor can be significantly increased. NMR probes can be formed by a method which includes wrapping a conductive wire ( 16 ) around a coil form ( 18 ) to produce a coil precursor assembly. The probe matrix ( 24 ) can be formed around the conductive wire and coil form with a matrix material using any suitable technique such as soft lithography and/or molding. The coil form can be removed from the probe matrix leaving a void sample volume ( 28 ) in the probe matrix. Advantageously, the NMR probes of the present invention allow for fill-factors approaching and achieving 100%.
1. An NMR probe, comprising:
a) a probe matrix having a uniform composition, an inner surface of the probe matrix defining a void sample volume therein; and
b) a conductive coil at least partially embedded in the probe matrix.
2. The probe of claim 1 , wherein the void sample volume is a cylindrical cavity.
3. The probe of claim 2 , wherein the cylindrical cavity has a diameter from about 50 μm to about 200 μm.
4. The probe of claim 1 , wherein the NMR probe is a micro-NMR probe.
5. The probe of claim 1 , wherein the void sample volume is a non-cylindrical cavity.
6. The probe of claim 1 , wherein the probe has a fill-factor of about 97% to 100%.
7. The probe of claim 6 , wherein the fill-factor is about 100%.
8. The probe of claim 1 , wherein the probe matrix comprises a material selected from the group consisting of polydimethylsiloxane, polytetrafluoroethylene, polyethylene, polypropylene, spin-on glass, and combinations thereof.
9. The probe of claim 1 , wherein the void sample volume has interior walls coated with a nano-film.
10. A method of forming an NMR probe, comprising:
a) forming a conductive coil embedded in a probe matrix having a uniform composition, an inner surface of the probe matrix defining a void sample volume at least partially within an interior volume of the conductive coil.
11. The method of claim 10 , wherein the step of forming includes:
a) wrapping a conductive wire around a cylindrical form to produce a coil precursor assembly;
b) forming the probe matrix around the conductive wire and cylindrical form with a matrix material; and
c) removing the cylindrical form leaving the void sample volume in the probe matrix.
12. The method of claim 11 , wherein the cylindrical form is a needle, polytetrafluoroethylene fiber, optical fiber, or combination or composite thereof.
13. The method of claim 11 , wherein the step of forming further includes orienting a mold around the coil precursor assembly and at least partially filling the mold with the matrix material.
14. The method of claim 10 , wherein the step of forming includes a deposition process or soft lithography process.
15. The method of claim 10 , wherein the probe matrix comprises a material selected from the group consisting of polydimethylsiloxane, polytetrafluoroethylene, polyethylene, and combinations thereof.
16. The method of claim 11 , wherein wrapping the cylindrical form leaves substantially no space between wrapped portions of the conductive wire and the cylindrical form.
17. The method of claim 10 , wherein the NMR probe has a fill-factor of about 90% to 100%.
18. The method of claim 10 , further comprising the step of coating the void sample volume in the probe matrix with a nano-film.
19. A method of using a probe including a probe matrix having a uniform composition, an inner surface of the probe matrix defining a void sample volume therein, and a conductive coil at least partially embedded in the probe matrix, the method comprising:
a) operatively connecting the NMR probe to a micro-NMR unit within a magnetic field;
b) inserting a fluid test sample within the void sample volume;
c) applying an electrical current to the conductive coil; and
d) detecting an output radio frequency and calculating an NMR spectrum for the test sample.
20. The method of claim 19 , wherein the NMR probe has a fill factor of about 100%.
21. The method of claim 19 , wherein the probe is disposed of after a single use.