The nanoscale system we will be studying in lab is a silver colloid. A very similar
procedure can be used for gold nanoparticles, but only silver will be described here. The
colloid is made of nanoscale silver particles suspended in an aqueous solution. The
particles are negatively charged and in the solution and they remain suspended due to the
repulsion of the negative charges between the particles. If we add an electrolyte to our
colloid solution, we can aggregate the colloidal particles into clusters and even form a
monolayer of silver particles. This monolayer will sink to the bottom of the vial. As this
occurs, the optical properties of the colloid are changing. We will use visible absorption
spectroscopy to measure the changes in the colloid by measuring the absorbed
wavelengths (color change of the colloid) as the silver precipitates out of the solution.