Detection of biomarkers using plasmonic gratings
The invention broadly relates techniques for imaging and medical diagnosis and, more particularly, to the fabrication of flexible plasmonic gratings and the use thereof in detection of biomarkers. A first aspect of the invention provides for techniques for the fabrication of novel, flexible plasmonic gratings that can be inexpensively fabricated onto fiber optic cables, flexible films and substrates with non-uniform surfaces to enhance the imaging resolution. A second aspect of the invention provides for an ultra¬high sensitivity (single molecule counting) biomarker detection platform useable for medical diagnosis based on a fluorescent sandwich ELISA assay performed on a plasmonic grating platform incorporated with a fluorescence detection unit.
1. A method of fabricating a fluorescence-enhancing, flexible, nanoscale plasmonic grating, comprising:
exposing a master mold to a hydrophilicity agent such that surface methyl groups of the master mold are converted to hydroxyl groups and carboxyl groups, wherein the master mold is hydrophobic prior to exposure to the hydrophilicity agent;
spin coating the master mold with a grating material;
curing the grating material to produce a flexible nanoscale polymer grating in the master mold;
removing the flexible nanoscale polymer grating from the master mold;
coating the flexible nanoscale polymer grating in a fluorescence-enhancing reflective layer;
coating the fluorescence-enhancing reflective layer with a protective capping layer, the protective capping layer comprising a corrosion resistant material; and
applying an adhesion layer to the protective capping layer.
2. The method of claim 1 , wherein the hydrophilicity agent is oxygen plasma, and wherein the master mold is exposed to the oxygen plasma for approximately 30 seconds at a power of approximately 7 watts.
3. The method of claim 1 , wherein the grating material is selected from a set consisting of Norland Optical adhesive (NOA) 71, NOA 73 and NOA 81.
4. The method of claim 1 , wherein the flexible nanoscale polymer grating is between approximately 40 micrometers and approximately 110 micrometers thick.
5. The method of claim 1 , wherein the method further comprises:
positioning a plastic substrate over the grating material; and
exposing the master mold, the grating material, and the plastic substrate to vacuum for at least ten minutes prior to curing the grating material.
6. The method of claim 1 , wherein curing the grating material comprises exposing the grating material to a 6-Watt UV light source for at least 40 minutes.
7. The method of claim 1 , wherein the flexible nanoscale polymer grating is between approximately 500 micrometers and 2 millimeters thick.
8. The method of claim 1 , wherein the fluorescence-enhancing reflective layer is a silver layer and is approximately 100 nanometers thick.
9. The method of claim 1 , comprising:
applying the flexible nanoscale polymer grating to a flexible media.
10. The method of claim 9 , wherein the flexible media comprises one of: a fiber optic cable, a polymer film, or a tape.
11. The method of claim 1 , comprising:
applying an additional adhesion layer to the flexible nanoscale polymer grating prior to coating the flexible nanoscale polymer grating in the fluorescence-enhancing reflective layer.
12. The method of claim 11 , wherein the additional adhesion layer comprises at least one of: chromium, chromia, germanium, titanium, or titania.
13. The method of claim 1 , wherein the protective capping layer comprises a non-reactive material that comprises at least one of: alumina, silica, or titania.
14. The method of claim 1 , wherein coating the fluorescence-enhancing reflective layer with the protective capping layer comprises:
pulsing water and trimethylaluminum over the fluorescence-enhancing reflective layer, the water and the trimethylaluminum forming an alumina capping layer, the alumina capping layer defining at least a portion of the protective capping layer comprising a non-reactive material.
15. The method of claim 1 , wherein the adhesion layer is between 0.1 and 20 nanometers thick, and wherein the adhesion layer comprises at least one of: a polymer, a two-dimensional material, or a nanoparticle material.
16. The method of claim 15 , wherein the adhesion layer comprises the polymer and wherein the polymer comprises polystyrene, and wherein the polymer comprises a thin film of from 1 to 5 nanometers thick.
17. The method of claim 15 , wherein the adhesion layer comprises the two-dimensional material and wherein the two-dimensional material comprises carboxylated graphene oxide.
18. The method of claim 15 , comprising:
subjecting the adhesion layer to a plasma treatment or an x-ray treatment.
19. The method of claim 15 , comprising:
applying a cross-linker to the adhesion layer.
20. The method of claim 1 , wherein the fluorescence-enhancing, flexible, nanoscale plasmonic grating enhances fluorescence by a factor of at least 100 as compared to a glass substrate.