In this thesis an in depth analysis of nanoparticle synthesis utilizing carbon monoxide as a reducing agent is presented. Synthesized nanoparticle mono and polydispersity was examined via particle distribution profiles, statistical, and spectral analysis and compared against other reduction methods. The size and monodispersity of the gold nanoparticles produced with carbon monoxide were tunable by altering the concentration of HAuCl 4 and gas injection flow rates. The carbon monoxide based reduction method offered excellent tunability over a broad range of sizes while maintaining a high level of monodispersity when compared to the other reduction methods. The mechanisms involved in the size dependent optical response of the synthesized nanoparticles were identified. It was also found that speciation of aqueous HAuCl 4 influences the size, structure, and properties of Au colloids. Ensemble extinction spectra and TEM images provide clear evidence that CO reduction offers a high level of tunability compared to other synthesis methods.