Composite particles

1. A composite particle comprising a core and a gold shell, wherein the core comprises a dielectric component and a magnetic component, wherein the dielectric component is a surface-modified inorganic oxide, the gold shell is directly contacting the magnetic component and the dielectric component is not surface modified with a natural or synthetic polymer.

2. The composite particle of claim 1 wherein the inorganic oxide is selected from the group consisting of silica (SiO 2 ), Nb 2 O 5 , Cr 2 O 3 , ZrO 2 , ZnO, CdO, CeO 2 , WO 3 , Al 2 O 3 (alumina), TiO 2 (titania), and mixtures thereof.

3. The composite particle of claim 1 wherein the magnetic component comprises Fe 3 O 4 , FePt, CoFe 2 O 4 , M*Fe 2 O 4 , or a surface modified version thereof, wherein M* is a divalent cation.

4. The composite particle of claim 1 further comprising at least one oligonucleotide, wherein the oligonucleotide is bound to the gold shell.

5. The composite particle of claim 4 wherein the oligonucleotide is bound to the gold shell via a thiol moiety.

6. The composite particle of claim 1 , wherein the magnetic component comprises iron.

7. The composite particle of claim 1 , wherein the surface modified inorganic oxide comprises amino-modified silica.

8. The composite particle of claim 1 , wherein the gold shell is deposited on the magnetic component.

9. A method for identifying a target compound in a sample containing or suspected of containing said target compound comprising the steps of

a) contacting the sample with (i) a first composite particle of claim 4 , wherein the oligonucleotide of said first composite particle hybridizes to at least a first portion of the target compound and (ii) a second composite particle of claim 4 , wherein the oligonucleotide of said second composite particle hybridizes to at least a second portion of the target compound, under conditions that permit complex formation between said oligonucleotide of said first composite particle and said first portion of said target compound and between said oligonucleotide of said second composite particle and said second portion of said target compound, and

b) detecting the composite particles bound to said target compound, wherein said detecting identifies the target compound in the sample.

10. A method for identifying a target compound in a sample containing or suspected of containing said target compound comprising the steps of

a) contacting the sample with a composite particle of claim 1 , wherein the composite particle is modified on its surface with a moiety selected from the group consisting of an oligonucleotide, a polypeptide, a polymer, a polysaccharide, an antibody, a lectin, and an antigen, and wherein said moiety interacts with said target compound to form a complex;

b) removing said complex formed in step (a) from the sample using a magnetic field; and

c) identifying the target compound using an analytic technique.

11. A method for separating a target compound in a mixture comprising the steps of

a) contacting the mixture with (i) a composite particle of claim 1 , wherein the composite particle is modified on its surface with a moiety selected from the group consisting of an oligonucleotide, a polypeptide, a polymer, a polysaccharide, an antibody, a lectin, and an antigen, and wherein said moiety interacts with said target compound to form a complex with the target compound, and (ii) a detectable probe modified on its surface with a moiety selected from the group consisting of an oligonucleotide, a polypeptide, a polymer, a polysaccharide, an antibody, a lectin, and an antigen, and wherein said moiety interacts with said target compound to form a complex with the target compound, under conditions that allow the composite particle and detectable probe to form an aggregate with the target compound; and

b) removing said aggregate formed in step (a) from the sample using a magnetic field, thereby separating the target compound from the mixture.