Synthesis and Analysis of Gold Nanoparticles by Citrate Reduction Experimental Objective: In this experiment, you will synthesize gold nanoparticles and explore the influence of the ratios of reactants and pH on the size of the nanoparticles as determined by transmission electron microscopy. You will also explore the influence of the size of the nanoparticles on the surface plasmon resonance measured using visible spectroscopy. Learning Objectives: Explain the basic red-ox chemistry of gold involved in nanoparticle synthesis. Explain the relationship between reaction conditions and nanoparticle size. Describe the relationship between the size of nanoparticles and their visual properties. Manipulate data sets in order to display them in relevant and meaningful ways. Collaborate with other groups to expand the context of your results. Theory: Most chemicals have properties determined almost entirely by their chemical composition. For example, elemental gold always has the same general properties. As the size of a solid decreases into the nanoscale regime, this can begin to change however. Many of the properties begin to depend on the size of the material, including the optical, electrical, chemical, and catalytic properties. Gold for example is typically a yellowish colored, lustrous material. As the size of a particle of gold shrinks below around 100 nm, it gives rise to blue to red solutions when suspended in water. The size and shape of the particle both influence the exact color which is observed. This is due to a phenomenon referred to as surface plasmon resonance. This basically refers to free electrons in the gold moving as a result of their interaction with the light shining on the particles. This leads to some of the wavelengths of light being absorbed while others are transmitted. The exact wavelengths which are absorbed are very sensitive to the exact size and shape of the particles. This effect is also highly dependent on what is surrounding the particles. Switching the solvent from water to something else like ethanol significantly alters the color of the particles. As a result, there is significant interest in using gold nanoparticles in sensing applications (among many others). In this lab, you will synthesize gold nanoparticles and explore the relationship between reaction conditions and the size of the particles as well as the influence of the size of the particles on the absorbance of light.