Surface enhanced Raman spectroscopy using shaped gold nanoparticles
In one aspect, the invention relates to methods for enhancing a Raman signal comprising the steps of providing a sample comprising a metal surface, an analyte adhered to the surface, and a metallic nanoparticle coupled to the surface, wherein the nanoparticle has a plasmon resonance band; exposing the sample to incident energy of an excitation wavelength; and detecting the Raman signal of the analyte. In a further aspect, the invention relates to a compositiion comprising a metal surface, a functionalized self-assembled monolayer adhered to the surface, wherin the self-assembled monolayer comprises an analyte, and a cetyltrimethylammonium halide-capped metallic nanoparticle coupled to the surface. In a further aspect, the invention relates to a cetyltrimethylammonium bromide-capped gold nanoparticle and a method for preparing same. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.
1. A method for enhancing a Raman signal comprising the steps of:
a. providing a sample comprising:
i. a metal surface,
ii. an analyte adhered to the metal surface, and
iii. a metallic shaped nanoparticle coupled to the metal surface by electrostatic immobilization, wherein the nanoparticle has a plasmon resonance band;
b. exposing the sample to incident energy of an excitation wavelength that overlaps with the metallic nanoparticle plasmon resonance band; and
c. detecting the Raman signal of the analyte.
2. The method of claim 1 , wherein the surface comprises at least one of gold, silver, copper, or silicon or a mixture or an alloy thereof.
3. The method of claim 1 , wherein the analyte comprises a thiol moiety.
4. The method of claim 1 , wherein the analyte comprises a carboxylic acid moiety.
5. The method of claim 1 , wherein the analyte comprises a portion of a functionalized self-assembled monolayer.
6. The method of claim 1 , wherein the nanoparticle comprises at least one of gold, silver, or copper or a mixture or an alloy thereof.
7. The method of claim 1 , wherein the nanoparticle comprises a cetyltrialkylammonium halide-capped metallic nanoparticle.
8. The method of claim 1 , wherein the nanoparticle comprises a cetyltrialkylammonium bromide-capped metallic nanoparticle.
9. The method of claim 1 , wherein the nanoparticle comprises a cetyltrimethylammonium bromide-capped metallic nanoparticle.
10. The method of claim 1 , wherein the nanoparticle has a shape comprising a cube, a block, a tetrapod, a sphere, a rod, a star, or a dogbone.
11. The method of claim 1 , wherein the nanoparticle has a shape comprising a cube and the plasmon resonance band comprises a wavelength maximum of about 540 nm.
12. The method of claim 1 , wherein the nanoparticle has a shape comprising a sphere and the plasmon resonance band comprises a wavelength maximum of about 520 nm.
13. The method of claim 1 , wherein the nanoparticle has a shape comprising a rod with an aspect ratio of from about 3.2 to about 16 and the plasmon resonance band comprises a longitudinal wavelength maximum of from about 685 nm to about 1200 nm and a transverse wavelength maximum of about 520 nm.
14. The method of claim 1 , wherein the nanoparticle has a shape comprising a rod with an aspect ratio of greater than about 16 and the plasmon resonance band comprises a wavelength maximum of greater than about 1200 nm.
15. The method of claim 1 , wherein the nanoparticle has a shape comprising a tetrapod or a dogbone and the plasmon resonance band comprises a wavelength of about 633 nm.
16. The method of claim 1 , wherein the incident energy is provided by a HeNe laser.
17. The method of claim 1 , wherein the excitation wavelength comprises a wavelength of about 633 nm.
18. The method of claim 1 , wherein the Raman signal has an enhancement factor of from about 10 7 to about 10 9 relative to the analyte in solution.
19. The method of claim 1 , wherein the nanoparticle has a shape comprising a cube, a block, a tetrapod, a rod with an aspect ratio of at least about 3.2, or a dogbone and the Raman signal has an enhancement factor of from about 10 1 to about 10 2 relative to the analyte in a sample comprising a spherical nanoparticle.
20. A method for enhancing a Raman signal comprising the steps of:
a. providing a sample comprising:
a metal surface,
ii. a functionalized self-assembled monolayer adhered to the metal surface, wherein the self-assembled monolayer comprises an analyte, and
iii. a cetyltrimethylammonium bromide-capped metallic shaped nanoparticle coupled to the metal surface by electrostatic immobilization;
b. exposing the sample to incident energy of an excitation wavelength; and
c. detecting the Raman signal of the analyte.
21. The method of claim 20 , wherein the nanoparticle has a plasmon resonance band and the excitation wavelength overlaps with the metallic nanoparticle plasmon resonance band.
22. The method of claim 20 , wherein the surface comprises at least one of gold, silver, copper, or silicon or a mixture or an alloy thereof.
23. The method of claim 20 , wherein the analyte comprises a thiol moiety.
24. The method of claim 20 , wherein the analyte comprises a carboxylic acid moiety.
25. The method of claim 20 , wherein the nanoparticle comprises at least one of gold, silver, or copper or a mixture or an alloy thereof.
26. The method of claim 20 , wherein the nanoparticle has a shape comprising a cube, a block, a tetrapod, a sphere, a rod, a star, or a dogbone.
27. The method of claim 20 , wherein the nanoparticle has a shape comprising a cube and the plasmon resonance band comprises a wavelength maximum of about 540 nm.
28. The method of claim 20 , wherein the nanoparticle has a shape comprising a sphere and the plasmon resonance band comprises a wavelength maximum of about 520 nm.
29. The method of claim 20 , wherein the nanoparticle has a shape comprising a rod with an aspect ratio of from about 3.2 to about 16 and the plasmon resonance band comprises a longitudinal wavelength maximum of from about 685 nm to about 1200 nm and a transverse maximum of about 520 nm.
30. The method of claim 20 , wherein the nanoparticle has a shape comprising a rod with an aspect ratio of greater than about 16 and the plasmon resonance band comprises a wavelength maximum of greater than about 1200 nm.
31. The method of claim 20 , wherein the nanoparticle has a shape comprising a tetrapod or a dogbone and the plasmon resonance band comprises a wavelength of about 633 nm.
32. The method of claim 20 , wherein the incident energy is provided by a HeNe laser.
33. The method of claim 20 , wherein the excitation wavelength comprises a wavelength of about 633 nm.
34. The method of claim 20 , wherein the Raman signal has an enhancement factor of from about 10 7 to about 10 9 relative to the analyte in solution.
35. The method of claim 20 , wherein the nanoparticle has a shape comprising a cube, a block, a tetrapod, a rod with an aspect ratio of at least about 3.2, or a dogbone and the Raman signal has an enhancement factor of from about 10 1 to about 10 2 relative to the analyte in a sample comprising a spherical nanoparticle.
36. A method for enhancing a Raman signal comprising the steps of:
a. providing a sample comprising:
i. a gold surface,
ii. a functionalized self-assembled monolayer adhered to the gold surface, wherein the self-assembled monolayer comprises an analyte, and
iii. a cetyltrimethylannnonium bromide-capped metallic shaped nanoparticle coupled to the surface by electrostatic immobilization;
b. exposing the sample to incident energy of an excitation wavelength that overlaps with the metallic nanoparticle plasmon resonance hand; and
c. detecting the Raman signal of the analyte, wherein the Raman signal has an enhancement factor of from about 107 to about 109 relative to the analyte in solution.