Composite beads comprising magnetizable substance and electro-conductive substance

1. A bead, which bead comprises:

a) a magnetizable substance; and

b) an electrically conductive substance, and

an optical labeling substance selected from the group consisting of a fluorescent substance, a scattered-light detectable particle and a quantum dot;

wherein the bead has a size of at least 0.1 μm.

2. The bead of claim 1 , wherein the quantum dot comprises a Cd-X core, X being Se, S or Te.

3. The bead of claim 2 , wherein the quantum dot is passivated with an inorganic coating shell.

4. The bead of claim 3 , wherein the coating shell comprises Y-Z, Y being Cd or Zn, and Z being S or Se.

5. The bead of claim 1 , wherein the quantum dot comprises a Cd-X core, X being Se, S or Te, a Y-Z shell, Y being Cd or Zn, and Z being S or Se, and the bead is further overcoated with a trialkylphosphine oxide.

6. The bead of claim 1 , which further comprises a plurality of optical labeling substances.

7. The bead of claim 6 , which comprises at least two different types of optical labeling substances.

8. The bead of claim 1 , which comprises a plurality of quantum dots.

9. The bead of claim 8 , wherein at least two quantum dots have different sizes.

10. The bead of claim 1 , wherein the quantum dot has a size ranging from about 1 nm to about 100 nm.

11. The bead of claim 1 , which has a size up to about 100 μm.

12. The bead of claim 1 , which has a spherical, a cubical or other regular or irregular shape.

13. The bead of claim 1 , which has a magnetizable substance core coated with an electrically conductive substance, a quantum dot and a binding partner that is capable of binding to a moiety.

14. The bead of claim 1 , wherein the bead has a size ranging from 0.3 μm to about 20 μm.

15. The bead of claim 1 , further comprising a stable polymeric coating.

16. A bead, which bead comprises:

a) a magnetizable substance; and

b) an electrically conductive substance,

wherein the bead has a size of at least 0.1 μm,

and wherein the magnetic substance comprises a transition metal composition or alloy selected from the group consisting of cobalt, manganese, tantalum, zirconium and cobalt-tantalum-zirconium (CoTaZr) alloy.

17. The bead of claim 16 , further comprising a quantum dot.

18. A bead, which bead comprises:

a) a magnetizable substance; and

b) an electrically conductive substance,

wherein the bead has a size of at least 0.1 μm,

wherein the electrically conductive substance is selected from the group consisting of gold, silver, and a conductive polymer.

19. The bead of claim 18 , wherein the conductive polymer is a polyaniline, a polypyrrole, or a polythiophene.

20. A bead, which bead comprises:

a) a magnetizable substance; and

b) an electrically conductive substance,

and a binding partner that is capable of specifically binding to a moiety.

21. The bead of claim 20 , wherein the binding partner is selected from the group consisting of a cell, a cellular organelle, a virus, a molecule and an aggregate or complex thereof.

22. A bead, which bead comprises:

a) a magnetizable substance; and

b) an electrically conductive substance,

and a quantum dot.

23. The bead of claim 22 , which further comprises a binding partner that is capable of specifically binding to a moiety.

24. The bead of claim 23 , wherein the binding partner is selected from the group consisting of a cell, a cellular organelle, a virus, a molecule and an aggregate or complex thereof.

25. A bead, which bead comprises:

a magnetizable substance; and

a quantum dot, which quantum dot comprises a Cd-X core, X being Se, S or Te, a Y-Z shell, Y being Cd or Zn, and Z being S or Se,

wherein the bead is further overcoated with a trialkylphosphine oxide.