Water-soluble fluorescent nanocrystals

• US 6,444,143 B2
• Filed: 05/29/2001
• Issued: 09/03/2002
• Est. Priority Date: 09/18/1998
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Lee, Jin-Kyu, Bawendi, Moungi G., Mikulec, Frederick V.
• Primary Examiner(s): Koslow, C. Melissa
• Application Number:
  US09/865,513
• Publication Number:
  US 20010040232A1
• Time in Patent Office: 462 Days
• Field of Search: 252/301.4 R, 252/301.4 S, 252/301.6 R, 252/301.6 S, 428/690, 428/403, 428/407
• US Class Current: 252/301.60S
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01B 19/007 Tellurides or selenides of metals C01B19/002 takes precedence
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: G01N 33/533 with fluorescent label
• CPC Class Codes: G01N 33/588 with semiconductor nanocrystal label, e.g. quantum dots
• CPC Class Codes: Y10T 428/2991 Coated
• CPC Class Codes: Y10T 428/2998 including synthetic resin or polymer

Abstract

A water soluble semiconductor nanocrystal capable of light emission is provided, including a quantum dot having a selected band gap energy, a layer overcoating the quantum dot, the overcoating layer comprised of a material having a band gap energy greater than that of the quantum dot, and an organic outer layer, the organic layer comprising a compound having a least one linking group for attachment of the compound to the overcoating layer and at least one hydrophilic group space apart from the linking group by a hydrophobic region sufficient to prevent electron charge transfer across the hydrophobic region. The particle size of the nanocrystal core is in the range of about 12Å to about 150Å, with a deviation of less than 10% in the core. The coated nanocrystal exhibits photoluminescende having quantum yield of greater than 10% in water.

Claims

1. A water-soluble semiconductor nanocrystal comprising:

a non-doped semiconductor material having a selected band gap energy;

a layer overcoating the semiconductor material, the overcoating layer comprised of a material having a band gap energy greater than that of the semiconductor material; and

an outer layer comprising a compound having at least one linking group for attachment of the compound to the overcoating layer and at least one hydrophilic group spaced apart from the linking group by a hydrophobic region sufficient to prevent charge transfer across the hydrophobic region.

2. The water-soluble nanocrystal of claim 1, wherein each linking group independently comprises a moiety selected from the group consisting of amines, thiols, phophines, phosphine oxides, and amine oxides.

3. The water-soluble nanocrystal of claim 1, wherein the hydrophilic group is a charged or polar group.

4. The water-soluble nanocrystal of claim 1, wherein the hydrophilic group is selected from the group consisting of carboxylic acid, carboxylate, sulfonate, hydroxide, alkoxide, ammonium salt, and phosphate.

5. The water-soluble nanocrystal of claim 1, wherein the hydrophilic group comprises an unsaturated hydrophilic group that is crosslinkable or polymerizable.

6. The water-soluble nanocrystal of claim 7, wherein the unsaturated hydrophilic group is selected from the group consisting of methacrylic acid, acrylic acid, and hydrophilically derivatized styrene.

7. The water-soluble nanocrystal of claim 1, wherein the compound comprises two or more hydrophilic groups.

8. The water-soluble nanocrystal of claim 1, wherein the hydrophobic region is selected from the group consisting of an alkane, an alkene and derivatives thereof modified to include moieties capable of attractive interaction with each other.

9. The water-soluble nanocrystal of claim 1, wherein the hydrophobic region comprises a hydrocarbon chain of the formula —

(CH₂)_n—

, where n is greater than or equal to six.

10. The water-soluble nanocrystal of claim 9, wherein n≧

8.

11. The water-soluble nanocrystal of claim 9, wherein n≧

10.

12. The water-soluble nanocrystal of claim 1, wherein the hydrophobic regions of adjacent compounds being crosslinked or polymerized to each other.

13. The water-soluble nanocrystal of claim 1, wherein the compound comprises the formual H_zX((CH₂)_n)CO₂H)_y and salts thereof, where X is N, P, or O═

P;

n≧

6; and

z and y are selected to satisfy the valency requirements of X.

14. The water soluble nanocrystal of claim 1, wherein the compound comprises the formula

where X and X′ are the same or different and are S, N, P or O═

P;

X and X′

may include other substitituents in order to satisfy valence requirements;

atoms bridging X and X′

are selected to form a 5-membered to 8 membered ring upon coordination to the semiconductor surface;

Y is a hydrophilic moiety; and

Z is a hydrophilic region having a backbone of at least 6 atoms.

15. The water-soluble nanocrystal of claim 1, wherein the compound comprises the formula,

where X, X′

and X″

are the same or different and are S, N, P or O═

P;

X, X′ and

X″

may include other substituents in order to satisfy valence requirements;

atoms bridging X, X′ and

X″

are selected to form a 5-membered to 8-membered ring upon coordination to the semiconductor surface;

Y is a hydrophilic moiety; and

Z is a hydrophobic region having a backbone of at least 6 atoms.

16. The water-soluble nanocrystal of claim 1, wherein the compound comprises the formula,

where X is the same or different and is S, N, P or O═

P; and

X optionally includes other substituents in order to satisfy valence requirements, Y is a hydrophilic moiety, m is in the range about 3 to 200; and

n is in the range about 3 to 100, and each of R and R′

is an organic moiety.

17. The water-soluble nanocrystal of claim 1, wherein the compound is a multidentate ligand.

18. The water-soluble nanocrystal of claim 17, wherein the band gap energy of the overcoating layer is in the ultraviolet energy range.

19. The water-soluble nanocrystal of claim 17, wherein the band gap energy of the overcoating layer is in the visible energy range.

20. The water-soluble nanocrystal of claim 1, wherein the overcoating layer is selected from the group consisting of ZnS, ZnSe, CdSe, CdS, GaN, and magnesium chalcogenides.

21. The water-soluble nanocrystal of claim 1, wherein the band gap energy of the semiconductor material is in the near IR energy range.

22. The water-soluble nanocrystal of claim 1, wherein the band gap energy of the semiconductor material is in the visible energy range.

23. The water-soluble nanocrystal of claim 1, wherein the band gap energy of the semiconductor material is in the ultraviolet energy range.

24. The water-soluble nanocrystal of claim 1, wherein the semiconductor material is a member of a substantially monodisperse particle population.

25. The water-soluble nanocrystal of claim 1, wherein when irradiated the nanocrystal emits energy in a spectral range of no greater than about 40 nm at full width at half max (FWHM).

26. The water-soluble nanocrystal of claim 1, wherein the semiconductor material exhibits less than a 10% rms deviation in diameter.

27. The-water-soluble nanocrystal of claim 1, wherein when irradiated the nanocrystal emits energy in a spectral range of no greater than about 30 nm full width at half max (FWHM).

28. The water-soluble nanocrystal of claim 1, wherein when irradiated the nanocrystal emits energy in a spectral range of no greater than about 25 nm full width at half max (FWHM).

29. The water-soluble nanocrystal of claim 1, wherein the nanocrystal exhibits photoluminescence having quantum yields of greater than 10% in aqueous medium.

30. The water-soluble nanocrystal of claim 1, wherein the nanocrystal exhibits photoluminescence having quantum yields in the range of 10-30% in aqueous medium.

31. The water-soluble nanocrystal of claim 1, wherein the semiconductor material comprises YX, where Y is selected from the group consisting of Zn, Cd, and mixtures thereof and X is selected from the group consisting of S, Se, Te, and mixtures thereof.

32. The water soluble nanocrystal of claim 1, wherein the overcoating layer is comprises AB, where A is selected from the group consisting of Zn, Cd, Mg and mixtures thereof and B is selected from the group consisting of S, Se and Te, such that AB is not the same as the semiconductor material and AB has a higher band gap energy than the semiconductor material.

33. The water-soluble nanocrystal of claim 1, wherein the nanocrystal has an emission in the range of about 470 nm to about 650 nm.

34. The-water-soluble nanocrystal of claim 1, wherein the particle size of the semiconductor material is selected from the range of about 12 Å

to about 150 Å

.

35. The water-soluble nanocrystal of claim 1, wherein a spectral range of emission is selected from the spectrum in the range of about 470 nm to about 650 nm.

42. The water-soluble nanocrystal of claim 1, 36, or 37, wherein the semiconductor material is selected from the group consisting of ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, GaN, GaP, GaAs, GaSb, InP, InAs, InSb, AlS, ALP, AlAs, AlSb, PbS, PbSe, Ge, and Si and ternary and quaternary mixtures thereof.

36. A water-soluble semiconductor nanocrystal comprising:

a non-doped semiconductor material having a selected band gap energy and being a nanocrystal; and

an outer layer comprising a compound having at least one linking group for attachment of the compound to a layer overcoating the semiconductor material, and at least one hydrophilic group spaced apart from the linking group by a hydrophobic region sufficient to prevent electron charge transfer across the hydrophobic region.

37. A water soluble semiconductor nanocrystal comprising:

a non-doped semiconductor material having a selected band gap energy; and

a layer overcoating the semiconductor material, the overcoating layer comprised of a material having a band gap energy greater than that of the semiconductor material; and

a bilayer, the bilayer comprising an inner layer having an affinity for a surface of the layer overcaoting the semiconductor material and an outer layer having a hydrophilic group spaced apart from the inner layer by a hydrophobic region adjacent to the inner layer.

38. The water-soluble nanocrystal of claim 37, wherein the inner layer comprises a coordinating lyophilic compound.

39. The water-soluble nanocrystal of claim 38, wherein the coordinating lyophilic compound is selected from the group consisting of a trialkyl phosphine, phosphine oxide and an alkyl amine.

40. The water-soluble nanocrystal of claim 37, wherein the outer layer comprises a surfactant.

41. The water-soluble nanocrystal of claim 40, wherein the surfactant is selected from the group consisting of sodium dioctyl sulfosuccinate, C₁₂H₂₅(OCH₂CH₂)₂₃OH, C₁₈H₃₇(OCH₂CH₂)₁₀OH, C₁₈H₃₇(OCH₂CH₂)₂₀OH, and a sodium salt of acids.

43. A composition comprising:

a water-soluble nanocrystal including a semiconductor material having a selected band gap energy and an outer layer comprising at least one water-solubilizing moiety, the water-solubilizing moiety having at least one linking group for attachment of the compound to a layer overcoating the semiconductor material and at least one hydrophiloc group spaced apart from the linking group by a hydrophobic region sufficient to prevent electron charge transfer across the hydrophobic region, the water soluble nanocrystal dispersed or dissolved in an aqueous medium.

44. A water-soluble semiconductor nanocrystal comprising:

a semiconductor material having a selected band gap energy, wherein the semiconductor material is a member of a substantially monodisperse particle population;

a layer overcoating the semiconductor material, the overcoating layer comprised of a material having a band gap energy greater than that of the semiconductor material; and

an outer layer comprising a compound having at least one linking group for attachment of the compound to the overcoating layer and at least one hydrophilic group.

45. A water-soluble semiconductor nanocrystal comprising:

a semiconductor material having a selected band gap energy;

a layer overcoating the semiconductor material, the overcoating layer comprised of a material having a band gap energy greater than that of the semiconductor material; and

an outer layer comprising a compound having at least one linking group for attachment of the compound to the overcoating layer and at least one hydrophilic group,

wherein when irradiated the nanocrystal emits energy in a spectral range of no greater than about 40 nm at full width at half max (FWHM).

46. A water-soluble semiconductor nanocrystal comprising:

a semiconductor material having a selected band gap energy;

a layer overcoating the semiconductor material, the overcoating layer comprised of a material having a band gap energy greater than that of the semiconductor material; and

an outer layer comprising a compound having at least one linking group for attachment of the compound to the overcoating layer and at least one hydrophilic group,

wherein the nanocrystal exhibits photoluminescence having quantum yields of greater than 10% in aqueous medium.