Luminescent core/shell nanoparticles suitable for (F)RET-assays

1. Luminescent inorganic nanoparticles comprising:

(a) a core comprising a first metal salt or oxide; and

(b) a shell surrounding the core, wherein the shell is comprised of a second metal salt that is luminescent and has non-semiconductor properties, and

wherein

(i) said first metal salt or oxide is non-luminescent, or

(ii) said first metal salt or oxide is capable of being excited by excitation energy and transferring said excitation energy to said second metal salt which emits the excitation energy as luminescence.

2. Luminescent nanoparticles according to claim 1 , wherein the first metal salt of the core and the second metal salt of the shell comprise the same anion.

3. Luminescent nanoparticles according to claim 2 , wherein the anion is selected from phosphates, sulfates, or fluorides.

4. Luminescent nanoparticles according to claim 1 , having an average diameter based on their longest axis of less than 30 nm.

5. Luminescent nanoparticles according to claim 1 , wherein the average thickness of the shell does not exceed the average diameter of the core.

6. Luminescent nanoparticles according to claim 1 , wherein (a) the core is non-luminescent and (b) the shell comprises a luminescent metal atom.

7. Luminescent nanoparticles according to claim 6 , wherein the shell comprises said luminescent metal atom as a predominant metal component.

8. Luminescent nanoparticles according to claim 7 , wherein the core consists of LaPO 4 and the shell of TbPO 4 .

9. Luminescent nanoparticles according to claim 7 , wherein the shell comprises said luminescent metal atoms as a sole metal component.

10. Luminescent nanoparticles according to claim 6 , wherein the shell comprises said luminescent metal atom as dopant of a non-luminescent host material.

11. Luminescent nanoparticles according to claim 6 , wherein the luminescent metal atom is selected from Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Cr, Mn, or a combination thereof.

12. Luminescent nanoparticles according to claim 1 , wherein the core metal and the shell metal are selected from Ce, Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, or Yb.

13. Luminescent nanoparticles according to claim 1 , wherein the core metal is selected from Ce and the shell metal from Nd, Dy or Tb.

14. Luminescent nanoparticles according to claim 1 , wherein the core metal is Yb and the shell metal Er.

15. Luminescent nanoparticles according to claim 1 , wherein the core comprises the metal of the first metal salt or oxide as predominant metal component, or the shell comprises the metal of the second luminescent metal salt as predominant metal component, or both.

16. Luminescent nanoparticles according to claim 15 , wherein the core comprises the metal of the first metal salt or oxide as a sole metal component, or the shell comprises the metal of the second luminescent metal salt as a sole metal component, or both.

17. Luminescent nanoparticles according to claim 1 , wherein the core comprises the metal of the first metal salt or oxide as dopant of a host material, or the shell comprises the metal of the second luminescent metal salt as dopant of a host material, or both.

18. Luminescent nanoparticles according to claim 1 , wherein the core consists of LaPO 4 :Ce or CePO 4 and the shell of TbPO 4 .

19. A dispersion comprising the nanoparticles according to claim 1 contained in a fluid or solid medium.

20. The dispersion of claim 19 , wherein the fluid medium is selected from an organic or aqueous dispersion medium, coating composition, ink, dye, polymer composition, or aerosol.

21. The dispersion of claim 19 , wherein the solid medium is selected from a coating, ink, dye, or polymer composition.

22. A (F)RET bioassay method comprising observing an absence, presence, or a change in intensity, of a fluorescence resonance energy transfer between a fluorescent donor and a fluorescent acceptor, wherein at least one of said fluorescent donor and fluorescent acceptor is a nanoparticle according to claim 1 .

23. The (F)RET bioassay method of claim 22 , wherein the method is used for detecting a nucleic acid.

24. A process for the preparation of luminescent inorganic nanoparticles comprising the steps of:

preparing a first mixture comprising nanoparticle cores of a first metal salt or oxide in an organic medium,

reacting said first mixture, an anion source for the shell to be formed and a second mixture comprising shell-forming metal ions and an organic complexing agent for said metal ions at a temperature of 50 to 350° C. until a shell has formed around said nanoparticles cores of a second metal salt;

the resulting luminescent inorganic nanoparticles comprising:

(a) a core comprising a first metal salt or oxide; and

(b) a shell surrounding the core, wherein the shell is comprised of a second metal salt that is luminescent and has non-semiconductor properties, and wherein

(i) said first metal salt or oxide is non-luminescent, or

(ii) said first metal salt or oxide is capable of being excited by excitation energy and transferring said excitation energy to said second metal salt which emits the excitation energy as luminescence.

25. The process according to claim 24 , wherein the organic medium present in the first mixture and the organic complexing agent present in the second mixture are identical.

26. The process according to claim 24 , wherein the organic medium and the complexing agent are selected from mono- or di-alkyl amines wherein the alkyl groups have from 4 to 20 carbon atoms, phosphororganic compounds, polyols or sulfoxides.

27. The process according to claim 24 , further comprising the steps of synthesizing the nanoparticle cores in said organic medium followed by reacting the nanoparticle cores without prior isolation.

28. The process according to claim 24 , wherein the anion source is included in excess molar amounts based on the stoichometrically required amount for reacting with available shell-forming metal ions.

29. The process according to claim 28 , wherein the anion source is selected from phosphate, sulfate, or fluoride.