Magnetic resonance-based viscometers and methods
This invention relates generally to magnetic resonance (MR)-based methods and kits for measuring the viscosity of liquid samples.
1. A method for determining viscosity of a liquid, wherein the liquid comprises a solvent, the method comprising:
(i) exposing a sample comprising the liquid and two or more non-settling particles, each of the particles having a positive magnetic susceptibility and a magnetic moment of at least about 6 ×10 −16 emu per particle, to an applied magnetic field, wherein the applied magnetic field is of a strength sufficient to induce the particles to aggregate; and
(ii) measuring a change in a nuclear relaxation property of the solvent caused by aggregation of the particles in the applied magnetic field;
wherein a change in the nuclear relaxation property relates to the viscosity of the liquid.
2. The method of claim 1 , wherein the nuclear relaxation property of the solvent is a relaxation time of the solvent.
3. The method of claim 2 , wherein step (ii) comprises performing two or more measurements to determine the relaxation time of the solvent, wherein at least two of the measurements are performed over a time interval when the sample is exposed to the applied magnetic field.
4. The method of claim 3 , wherein the method further comprises determining a rate of relaxation time change by:
(a) calculating a difference between a relaxation time measured at a start of the time interval and a relaxation time measured at an end of the time interval; and
(b) dividing the difference calculated in step (a) by a duration of the time interval.
5. The method of claim 4 , wherein the method further comprises determining the viscosity of the liquid by locating the rate of relaxation time change for the sample on a plot of rates of relaxation time change versus 1/viscosity for two or more liquid standards, wherein viscosity for each standard is known.
6. The method of claim 2 , wherein the relaxation time is T2.
7. The method of claim 1 , wherein the solvent is water.
8. The method of claim 1 , wherein the solvent is an organic solvent.
9. The method of claim 1 , wherein the particle is a microparticle having a size greater than 100 nanometers to about 5 microns.
10. The method of claim 9 , wherein the microparticle is a superparamagnetic microparticle.
11. The method of claim 10 , wherein the microparticle comprises a superparamagnetic metal oxide.
12. The method of claim 9 , wherein the microparticles have an R2 relaxivity of at least about 1×10 8 s −1 per mM particle.
13. The method of claim 9 , wherein the microparticles have a magnetic moment of at least about 6×10 −12 emu per particle.
14. The method of claim 9 , wherein the microparticles have a size of from 1 to 5 microns.
15. The method of claim 14 , wherein the microparticles have a magnetic moment of at least about 6×10 −12 emu per particle.
16. The method of claim 1 , wherein the particle has a buoyant density that is about the same as that of the solvent.
17. The method of claim 16 , wherein the nanoparticles have an R2 relaxivity of at least about 1×10 8 s −1 per mM particle.
18. The method of claim 1 , wherein a hydrophilic or hydrophobic moiety is covalently linked to the particle.
19. The method of claim 1 , wherein a carboxylic acid group is covalently linked directly or indirectly to the particle.
20. The method of claim 1 , wherein the particles have an R2 relaxivity of at least about 1×10 8 s −1 per mM particle.