Gold Nano-Particles
To prepare the gold nano-particles for plating to the vials, they start as HAuCl₄ and are diluted to a 30% solution using DI water.  This solution must be kept in a refrigerator and in a black plastic bag to keep it from spoiling.  The solution is then added into a 4mm sodium citrate solution in a ratio of 13.3 mL sodium citrate to .602 mL of the gold solution.  The resulting solution is then sonicated under Nitrogen for 30 minutes to create the nano-particles.  These are then stored in a brown bottle to keep the gold from precipitating out, they should have a shelf life of 30 days.
We now think that the nano-particles must be made right before they are used, we don’t think that they have any kind of a shelf life.  We also think that they can’t scale up well, the color of the final product changes as the volume of the reaction increases and that might be changing their physical properties.

APTES Vials

1. Clean three times with ETOH with soication for 5 minutes each time
2. Dry at 70 degrees Celsius for 2 hours
3. Immerse in 1% APTES solution in anhydrous ETOH at 70 degrees Celsius for 2 hours
4. Clean three times with ETOH with soication for 5 minutes each time
5. Dry at 70 degrees Celsius for 2 hours

Plating for Vials
After much consternation the plating process seems to be well honed now, but we are still working on figuring out how much of the nano-particles to use for plating so we get good signal but don’t waste gold.  Currently 1 mL of nano-particles per 4 mL vial seems to be our best bet.  We put 1mL AuNP in the vial, then put in rotator at 10 RPM for 24 hours then rinse in DI water three times before doing the surface enhancement with ligands.

Creating the Ligand Monolayer
This is super easy, but very important.  All that must be done is adding a dilute (1 to 10 mM) solution of something like thiophenol or decanethiol  to the plated vials and letting them it for 24 hours.  Rinse with DI water and they’re ready for Surface Enhanced Raman Spectroscopy.

Taking a Raman Reading
After rinsing out the excess ligand mixture and taking a baseline shot with a Raman Spectrometer, a sample is put into the vial and shaken.  The sample water is then discarded an the vial is put into the Raman Spectrometer to take several readings.  The resulting spectra are then superimposed so as to see where the peaks have changed since the baseline, this gives the user a ‘fingerprint’ which can be matched to a known spectra to tell the user what contaminants are in the water sample.

Layer-By-Layer Coating

1. Clean vials 3x with ETOH, sonicating for 5 minutes each time
2. Oven dry / blow dry with nitrogen
3. Put polyethyleneimine in the vial, shake then let sit for 5 mins
4. Rinse with DI and blow dry with nitrogen
5. Put in AuNP for 10 mins on rotator
6. Rinse with DI then dry with nitrogen
7. Repeat steps 3-6 X times

Silver Dendrites (AgD)

1. Cut piece of zinc, clean with 20 mM HCl, dry
2. cover Zn with .2 M AgNO₃
3. Let sit 1 min
4. Scrape dendrites off zinc with a knife

A video of the reaction can be found here