ULTRASENSITIVE SERS FLOW DETECTOR

• US 20150338348A1
• Filed: 05/26/2015
• Published: 11/26/2015
• Est. Priority Date: 05/23/2014
• Status: Active Grant

• Current Assignee: University of Notre DAME Du Lac
• Original Assignee: University of Notre DAME Du Lac
• Inventors: Schultz, Zachary, Dada, Oluwatosin, Negri, Pierre, Jacobs, Kevin
• Granted Patent: US 9,804,093 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01N 15/1404 Handling flow, e.g. hydrodynamic focusing
• CPC Class Codes: G01N 15/1429 Signal processing
• CPC Class Codes: G01N 15/1434 Optical arrangements
• CPC Class Codes: G01N 2015/0053 in liquids, e.g. trouble
• CPC Class Codes: G01N 2015/1006 for cytology
• CPC Class Codes: G01N 2015/1413 Hydrodynamic focussing
• CPC Class Codes: G01N 2021/058 Flat flow cell
• CPC Class Codes: G01N 21/05 Flow-through cuvettes G01N21/09 takes precedence; handling fluid samples G01N1/10
• CPC Class Codes: G01N 21/658 enhancement Raman, e.g. surface plasmons

Abstract

The invention provides an apparatus and methods for label-free, chemical specific detection in flow for high throughput characterization of analytes in applications such as flow injection analysis, electrophoresis, and chromatography. A surface-enhanced Raman scattering (SERS) flow detector capable of ultrasensitive optical detection on the millisecond time scale has been developed. The device employs hydrodynamic focusing to improve SERS detection in a flow channel where a sheath flow confines analyte molecules eluted from a capillary over a planar SERS-active substrate. Increased analyte interactions with the SERS substrate significantly improve detection sensitivity. Raman experiments at different sheath flow rates showed increased sensitivity compared with the modeling predictions, indicating increased adsorption. At low analyte concentrations, rapid analyte desorption is observed, enabling repeated and high-throughput SERS detection. The flow detector offers substantial advantages over conventional SERS-based assays such as minimal sample volumes and high detection efficiency.

Claims

1. An apparatus for performing surface-enhanced Raman scattering (SERS) comprising:

a Raman microscope,

a flow cell,

an apparatus for supplying a sheath flow fluid to the flow cell,

a pressure source to pump fluid through a capillary,

a capillary leading from the pressure source to the flow cell, and

a detector for detecting light scattered by an analyte in solution,

wherein the pressure source is configured to transport an analyte in solution through the capillary to the flow cell, wherein the flow cell comprises;

an inlet port and an outlet port for a sheath flow fluid,

a planar noble metal SERS-active substrate,

the capillary that connects the pressure source to the SERS-active substrate of the flow cell, wherein the end of the capillary terminates at an analyte analysis zone accessible to a laser,

a flow channel extending from the end of the capillary to the analyte analysis zone for analysis by a laser, and which concurrently define a flow path between the inlet port and the outlet port, and

a flow cell cover through which a laser can be directed, which flow cell cover seals the flow cell to prevent fluid from escaping the flow cell except through the outlet port;

wherein the terminal end of the capillary is directed toward the surface of the SERS-active substrate and the flow cell is configured to perform hydrodynamic focusing on an analyte in solution.

2. The apparatus of claim 1 wherein the SERS-active substrate comprises a thin film of silver metal or gold metal.

3. The apparatus of claim 1 wherein the capillary leading to the flow cell is a fused silica capillary.

4. The apparatus of claim 1 wherein the capillary has an outer diameter of about 40 μ

m to about 300 μ

m.

5. The apparatus of claim 1 wherein the capillary has an outer diameter of about 50 μ

m to about 150 μ

m.

6. The apparatus of claim 1 wherein the capillary has an inner diameter of about 4 μ

m to about 100 μ

m.

7. The apparatus of claim 1 wherein the capillary has an inner diameter of about 10 μ

m to about 50 μ

m.

8. The apparatus of claim 1 wherein the Raman microscope includes a single longitudinal mode laser with a wavelength between about 632 nm and about 670 nm.

9. The apparatus of claim 1 wherein the sample capillary is connected to a direct output of a chemical separation for repeated analysis.

10. A method of detecting or characterizing an analyte in solution using the surface-enhanced Raman scattering (SERS) flow detector of claim 1, the method comprising:

contacting an analyte solution and a SERS-active substrate using hydrodynamic focusing to co-locate the analyte on the SERS-active substrate;

wherein the hydrodynamic focusing comprises passing a sheath fluid over the analyte in solution, wherein the ratio of the sheath flow rate to the capillary flow rate is at least 2;

1, thereby increasing the adsorption of analytes in the detection area of the SERS-active substrate;

conducting laser excitation of the analyte on the SERS-active substrate; and

detecting light scattered by the analyte in solution;

wherein the hydrodynamic focusing on the analyte solution confines the analyte at the SERS substrate, thereby increasing the frequency of interactions between the analyte and nanostructures of the SERS-active substrate, and improves the limit of detection for SERS detection.

11. The method of claim 10 wherein the ratio of the sheath flow rate to the capillary flow rate is about 2:

1 to about 70;

1.

12. The method of claim 10 wherein the ratio of the sheath flow rate to the capillary flow rate is about 12:

1 to about 50;

1.

13. The method of claim 10 wherein the ratio of the sheath flow rate to the capillary flow rate is about 25:

1 to about 45;

1.

14. The method of claim 10 wherein the sheath flow rate is about 50μ

L/min to about 360 μ

L/min.

15. The method of claim 10 wherein the sheath flow rate is about 150μ

L/min to about 200 μ

L/min.

16. The method of claim 10 wherein the range of particle size detection of the flow detector is about 3000 nm to about 50 nm.

17. The method of claim 10 wherein the lower detection limit of the flow detector for solutions is about 100 picomolar.

18. The method of claim 10 wherein the signal of the Raman spectra collected is enhanced by about 10⁶ to about 10⁸ compared to a corresponding spontaneous Raman analysis that does not employ hydrodynamic focusing and SERS.

19. The method of claim 10 wherein the signal of the Raman spectra collected is enhanced by about 10³ to 10⁴ compared to a corresponding SERS analysis that does not employ hydrodynamic focusing.

20. The method of claim 10 wherein the SERS-active substrate comprises a thin film of silver metal and the surface of the substrate resists fouling and lacks a memory effect of the analyte.