SUPERPARAMAGNETIC COLLOIDAL NANOCRYSTAL STRUCTURES

• US 20100224823A1
• Filed: 04/26/2008
• Published: 09/09/2010
• Est. Priority Date: 04/27/2007
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Yin, Yadong, Ge, Jianping
• Granted Patent: US 10,118,834 B2
• Time in Patent Office: Days
• US Class Current: 252/62.560
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01G 49/08 Ferroso-ferric oxide [Fe3O4]
• CPC Class Codes: C01P 2002/72 by d-values or two theta-values, e.g. as X-ray diagram
• CPC Class Codes: C01P 2002/80 defined by measured data other than those specified in group C01P2002/70
• CPC Class Codes: C01P 2004/04 obtained by TEM, STEM, STM or AFM
• CPC Class Codes: C01P 2004/32 Spheres
• CPC Class Codes: C01P 2004/62 Submicrometer sized, i.e. from 0.1-1 micrometer
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C01P 2004/84 one phase coated with the other
• CPC Class Codes: C01P 2006/42 Magnetic properties
• CPC Class Codes: C01P 2006/60 Optical properties, e.g. expressed in CIELAB-values
• CPC Class Codes: C09C 1/24 Oxides of iron
• CPC Class Codes: G02F 1/09 based on magneto-optical elements, e.g. exhibiting Faraday effect
• CPC Class Codes: G02F 2202/32 Photonic crystals

Abstract

Monodisperse colloidal nanocrystal clusters of magnetite (Fe₃O₄) with tunable sizes from about thirty to about three hundred nanometers have been synthesized using a high-temperature hydrolysis process. The colloidal nanocrystal clusters are capped with polyelectrolytes, and highly water soluble. Each cluster is composed of many single magnetite crystallites, thus retaining the superparamagnetic behavior at room temperature. The combination of superparamagnetic property, high magnetization, and high water dispersibility makes the colloidal nanocrystal clusters ideal candidates for various important biomedical applications such as drug delivery and bioseparation. The present invention is further directed to methods for forming colloidal photonic crystals from both aqueous and nonaqueous solutions of the superparamagnetic colloidal nanocrystal clusters with an external magnetic field applied thereto. The diffraction of the photonic crystals can be tuned from near infrared to visible and further ultraviolet spectral region by varying the external magnetic field.

Claims

1. A method for forming superparamagnetic magnetite colloidal nanocrystal clusters, comprising:

providing an iron salt precursor, a polar solvent, a surfactant, and a precipitation agent having a concentration;

mixing the iron salt precursor, the polar solvent, the surfactant, and the precipitation agent to initiate a hydrolysis reaction; and

obtaining superparamagnetic magnetite (Fe₃O₄) colloidal nanocrystal clusters from a mixture resulting from the hydrolysis reaction.

2. The method of claim 1, wherein the step of mixing comprises:

mixing the iron salt precursor, the polar solvent, and the surfactant to produce a first mixture; and

introducing the precipitation agent into the first mixture to initiate the hydrolysis reaction.

3. The method of claim 1, wherein the step of mixing comprises:

mixing the iron salt precursor and the polar solvent to produce a first mixture;

mixing the surfactant and the precipitation agent to produce a second mixture; and

introducing the second mixture into the first mixture to initiate the hydrolysis reaction.

4. The method of claim 1, wherein the average size of each of the nanocrystal clusters ranges from about thirty nanometers to about three hundred nanometers.

5. The method of claim 4, further comprising controlling the average size of the nanocrystal clusters.

6. The method of claim 5, wherein controlling the average size of the nanocrystal clusters includes modulating the concentration of the precipitation agent while keeping all other parameters fixed so as to obtain the nanocrystal clusters of a desired value of average size.

7. The method of claim 1, further comprising controlling the hydrolysis reaction to occur at a temperature ranging from about 100°

C. to about 320°

C.

8. The method of claim 1, wherein the superparamagnetic magnetite colloidal nanocrystal clusters are highly dispersible in aqueous solution.

9. The method of claim 1, wherein the iron salt precursor is chosen from the group consisting of iron (II) chloride, iron (III) chloride, iron (II) sulfate, iron (III) sulfate, iron (II) nitrate, iron (III) nitrate, iron (II) fluoride, iron (III) fluoride, iron (II) bromide, iron (III) bromide, iron (II) iodide, iron (III) iodide, iron (II) sulfide, iron (III) sulfide, iron (II) selenide, iron (III) selenide, iron (II) telluride, iron (III) telluride, iron (II) acetate, iron (III) acetate;

iron (II) oxalate, iron (III) oxalate, iron (II) citrate, iron (III) citrate, iron (II) phosphate and iron (III) phosphate.

10. The method of claim 1, wherein the polar solvent is chosen from the group consisting of chemical compounds containing multiple hydroxyl groups.

11. The method of claim 1, wherein the polar solvent is chosen from the group consisting of polyols including ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and polyethylene glycols.

12. The method of claim 1, wherein the surfactant is chosen from the group consisting of polyelectrolytes.

13. The method of claim 12, wherein the surfactant is chosen from the group consisting of polyelectrolytes containing carboxylate, sulfonate, sulfate, phosphate, amine, ammonium, betaine and sulfobetaine groups.

14. The method of claim 13, wherein the surfactant is chosen from the group consisting of polyelectrolytes containing carboxylic acid groups.

15. The method of claim 1, wherein the surfactant is chosen from the group consisting of polyacrylic acid and polymethacrylic acid.

16. The method of claim 1, wherein the precipitation agent is chosen from the group consisting of hydroxides, carbonates, bicarbonates, phosphates, hydrogen phosphate, ammonia, group 1 salts of carbanions, amides, hydrides, and dihydrogen phosphates of group 1, 2, and ammonium.

17. The method of claim 1, wherein obtaining nanocrystal clusters includes:

obtaining superparamagnetic magnetite (Fe₃O₄) colloidal nanocrystals from the second mixture resulting from the hydrolysis reaction, and

obtaining superparamagnetic magnetite (Fe₃O₄) colloidal nanocrystal clusters by the aggregation of the nanocrystals.

18. The method of claim 17, wherein the average size of each of the nanocrystals is of the order of ten nanometers.

19. The method of claim 18, wherein the average size of each of the nanocrystal clusters ranges from about thirty nanometers to about three hundred nanometers.

20. The method of claim 1, further comprising:

coating the nanocrystal clusters with a layer of silica or polymer; and

linking a ligand to the surface of the coated nanocrystal clusters.

21. A method of forming colloidal photonic crystals, comprising:

providing superparamagnetic magnetite colloidal nanocrystal clusters formed by the method of claim 1;

dispersing the nanocrystal clusters in an aqueous solution; and

applying an external magnetic field on the nanocrystal clusters so as to form the colloidal photonic crystals from assemblage of the nanocrystal clusters in the polar solution,

wherein the colloidal photonic crystals is tunable in lattice parameters and in diffraction frequency by varying the external magnetic filed.

22. The method of claim 21, wherein the polar solution is chosen from the group consisting of water, alcohols, and other aqueous solutions.

23. The method of claim 21, further comprising cleaning the colloidal photonic crystals, before applying the magnetic field, for removing extra surfactant on the nanocrystal clusters and decreasing ionic strength thereof.

24. The method of claim 21, wherein the diffraction frequency of the colloidal photonic crystals under varying the external magnetic filed covers the entire visible region, the near-ultraviolet region, and the near-infrared region of the light spectrum.

25. The method of claim 21, wherein when the external magnetic field is oscillating, the optical response of the colloidal photonic crystals follows the oscillation.

26. A method of forming colloidal photonic crystals, comprising:

providing superparamagnetic magnetite colloidal nanocrystal clusters formed by the method of claim 1;

modifying the surface of the nanocrystal clusters to be dispersible in nonaqueous solvents;

dispersing the nanocrystal clusters in a nonaqueous solution; and

applying an external magnetic field on the nanocrystal clusters so as to form the colloidal photonic crystals from assemblage of the nanocrystal clusters in the nonaqueous solution,

wherein the colloidal photonic crystals is tunable in lattice parameters and in diffraction frequency under varying the external magnetic filed.

27. The method of claim 26, wherein the nonaqueous solution is chosen from the group consisting of alkanol solvents.

28. The method of claim 26, wherein modifying the surface of the nanocrystal clusters includes coating the nanocrystal clusters with a silica layer.

29. The method of claim 26, further comprising the step of tuning the thickness of the silica layer for further tuning the diffraction frequency under the external magnetic filed.

30. The method of claim 26, wherein the diffraction frequency of the colloidal photonic crystals under varying the external magnetic filed covers the entire visible region, the near-ultraviolet region, and the near-infrared region of the light spectrum.

31. A method of forming a polymer matrix containing droplets of superparamagnetic colloidal photonic crystals, comprising:

providing superparamagnetic magnetite colloidal nanocrystal clusters formed by the method of claim 1;

providing a solid polymer matrix;

dispersing the nanocrystal clusters in an aqueous solution to produce a nanocrystal clusters solution;

embedding droplets of the nanocrystal clusters solution into the solid polymer matrix; and

applying an external magnetic field on the solid polymer matrix containing the nanocrystal cluster solution droplets so as to form colloidal photonic crystals in each of the droplets,

wherein the colloidal photonic crystals is tunable in lattice parameters and in diffraction frequency by varying the external magnetic filed.

32. A method of forming a polymer matrix containing droplets of superparamagnetic colloidal photonic crystals, comprising:

providing superparamagnetic magnetite colloidal nanocrystal clusters formed by the method of claim 1;

providing a solid polymer matrix;

modifying the surface of the nanocrystal clusters to be dispersible in nonaqueous solvents;

dispersing the nanocrystal clusters in a nonaqueous solution to produce a nanocrystal clusters solution;

embedding droplets of the nanocrystal clusters solution into the solid polymer matrix; and

applying an external magnetic field on the solid polymer matrix containing the nanocrystal cluster solution droplets so as to form colloidal photonic crystals in each of the droplets,

wherein the colloidal photonic crystals is tunable in lattice parameters and in diffraction frequency by varying the external magnetic filed.

33. The method of forming a polymer matrix of claim 32 further comprises, before applying the external magnetic field, curing the solid polymer matrix containing the nanocrystal cluster solution droplets.