What do colloids do?

Hello, everyone! I don’t know if you remember but this summer I’m working in Professor Kristin Wustholz’s lab using Surface-Enhanced Raman Scattering (SERS) to identify dyes in paintings created by Charles Willson Peale. When I came in this summer I had an official list of things I wanted to get done and learn. They were:

  • Synthesize stable silver nanoparticles (colloids)
  • Create a library of known red colorants for later comparisons with the art samples
  • Take samples with Shelley, a conservator at the Colonial Williamsburg Foundation, from areas of interest in Peale’s paintings to test

If you have read Kate Nelsen’s blog post “Have you ever watched colloids dry?”, you probably know that we have had problems synthesizing stable colloids. However, we are improving on our synthesis with new cleaning methods and checking the intensity of the boiling. Boiling affects how well the silver nitrate and sodium citrate react to form a suspension of silver, sodium citrate, and water. Low boiling = poor suspension = bad colloids.

But why do we care so much about the colloids?

Answer: Because the dyes I’m working with (carmine lake, madder lake, etc.) are organic dye molecules. Because of this, they fluoresce. In order to quench the fluorescence and amplify the signal, we need good colloids. When the colloids are stable and energized by a light source, in this case a 633 nm laser, the colloids create an electronic field that amplifies the vibrational bonds around it. Hopefully, our art samples are within that electronic field so that we get a SERS spectrum instead of fluorescence.

With good colloids and good SERS spectrum of reference red colorants, such as carmine lake, madder lake, and others, I can turn my attention to art samples!