Site specific fluorescence and contrast marker for same

1. A contrast marker for indicating a presence of a target cell in an environment, the contrast marker comprising:

a fluorophore;

a nanometal particle (NMP);

a short spacer and a long spacer, each directly linking said fluorophore to said NMP, wherein said short spacer holds said fluorophore at a quenching distance from said NMP and said long spacer holds said fluorophore at a fluorescence enhancing distance from said NMP;

wherein said NMP is coated with a targeting biomolecule configured to engage the target cells; and

wherein said short spacer is configured to be cleaved by a molecule characterizing the target cells;

whereby, before said short spacer is cleaved, said short spacer controls a distance between said fluorophore and said NMP to be the quenching distance, so that the fluorescence is quenched; and

whereby, after said short spacer is cleaved, said long spacer controls the distance between said fluorophore and said NMP to be the fluorescence enhancing distance, so that the fluorescence is enhanced.

2. The contrast marker of claim 1 , wherein said long spacer is configured to be biologically stable in the environment.

3. The contrast marker of claim 2 , wherein said NMP comprises a nano-sized gold particle (NGP).

4. The contrast marker of claim 3 , wherein the molecule characterizing the target cells comprises an enzyme secreted by the target cells.

5. The contrast marker of claim 4 , wherein said fluorophore comprises a derivative of Indocyanine Green (ICG).

6. The contrast marker of claim 4 , wherein said long spacer comprises a biocompatible polymer.

7. The contrast marker of claim 6 , wherein said long spacer comprises Poly(ethylene glycol) (PEG).

8. The contrast marker of claim 7 , wherein said short spacer comprises PEG having a G-G-R peptide sequence.

9. The contrast marker of claim 4 , wherein the target cell comprises a cancer cell.

10. The contrast marker of claim 9 , wherein said targeting biomolecule is selected from the group consisting of antibodies and aptamers.

11. A method for detecting a presence of a target cell in an environment, the method comprising:

providing the contrast marker of claim 1 in the environment containing the target cell;

applying an excitation light to the contrast marker; and

detecting fluorescence emitted from the contrast marker, thereby detecting the presence of the target cell in the environment;

whereby, before the short spacer is cleaved, the short spacer controls a distance between the fluorophore and the NMP to be the quenching distance, so that the fluorescence is quenched; and

whereby, after the short spacer is cleaved, the long spacer controls the distance between the fluorophore and the NMP to be the fluorescence enhancing distance, so that the fluorescence is enhanced.

12. The method of claim 11 ,

wherein the targeting biomolecule is configured to engage with a receptor of the target cell; and

wherein, when the targeting biomolecule engages the receptor, the enzyme cleaves the short spacer.

13. The method of claim 12 , wherein the target cell is a cancer cell.

14. The method of claim 12 , wherein the fluorophore comprises a derivative of Indocyanine Green (ICG).

15. The method of claim 14 , wherein the fluorophore comprises Cypate.

16. The method of claim 11 , wherein the providing comprises introducing the contrast marker into a blood stream of a patient.

17. A cancer contrast marker, comprising a fluorophore directly linked to a nanometal particle (NMP) by both a short spacer and a long spacer, wherein the short spacer holds the fluorophore at a quenching distance from the NMP and can be cleaved by enzymes secreted by cancer cells, and the long spacer holds the fluorophore at a fluorescence enhancing distance from the NMP;

wherein before the short spacer is cleaved, the short spacer controls a distance between said fluorophore and the NMP to be the quenching distance, so that the fluorescence is quenched; and

wherein after the short spacer is cleaved, the long spacer controls the distance between the fluorophore and the NMP to be the fluorescence enhancing distance, so that the fluorescence is enhanced.