COLLOIDAL GOLD NANOPARTICLE SOLUTIONS FOR SURFACE ENHANCED RAMAN SCATTERING

1 . A method of surface-enhanced Raman scattering testing for 1 to 10 ppm analyte using refrigerated 1 mL solutions of prepared colloidal gold nanoparticles having a position of the surface plasmon peak at 540 nm in a vial comprising:

sonicate said colloidal gold nanoparticles for 5 minutes in said vial and bring said colloidal gold nanoparticles to room temperature;

add 40 to 100 μL of said analyte that is dissolved in a solvent and an aggregating agent to said vial;

shake said vial to mix said colloidal gold nanoparticles, said analyte, and said aggregating agent together; and,

measure said vial containing said colloidal gold nanoparticles, said analyte, and said aggregating agent immediately with the Raman instrumentation configured for 785 nm laser excitation.

2 . The method of claim 1 for less than 1 ppm analyte wherein said colloidal gold nanoparticles are mixed with said analyte at a 1:4 colloidal gold nanoparticles:analyte ratio.

3 . The method of claim 1 wherein said aggregating agent is 2 to 10 μL of hydrochloric acid (HCl).

4 . The method of claim 1 wherein the synthesis of said prepared colloidal gold nanoparticles is tailored to achieve maximum enhancement from analytes with 785 nm laser excitation comprising: soaking A 250 mL Erlenmeyer flask in a base bath solution overnight;

thoroughly rinsing said flask with purified water and creating a solution by adding 200-300 mL of purified water and 0.05 to 0.06 grams HAuCl 4 ;

turn off any lights to prevent any interaction with gold salt;

bringing said solution to a boil with moderate magnetic stirring on a hot plate;

once boiling, the stirring is increased until a vortex is achieved in said solution;

then rapidly adding 0.05 to 0.06 grams sodium citrate to said solution, and continue boiling with rapid stirring for 14 minutes;

removing said flask from the hot plate and cooling said solution to room temperature;

cooling said resulting solution containing colloidal gold nanoparticles in a refrigerator; and,

once cooled, measuring said colloidal gold nanoparticles solution with absorption spectroscopy to confirm the position of the surface plasmon peak at 540 nm.

5 . The method of claim 4 for less than 1 ppm analyte wherein said colloidal gold nanoparticles are mixed with said analyte at a 1:4 colloidal gold nanoparticles:analyte ratio.

6 . The method of claim 4 wherein said aggregating agent is 2 to 10 μL of hydrochloric acid (HCl).