Dodecanethiol-stabilized gold nanoparticles of different sizes were synthesized using Bi-phasic reduction method by varying the concentration of stabilizer. These particles were characterized using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). TEM images show the average particle size of different samples ranging from ~1.7 nm to 5.7 nm. FTIR study confirms the linkage of thiol group and their partial crystalline self assembly onto the surface of nano gold particles. From the UV-Vis spectra, it is noticed that absorption peak position is sensitive to the size of the particles. Theoretical fit for absorbance spectra was obtained using Mie theory and the deviation from experimental results demonstrates the large size and shape distribution. A linear relationship between logarithms of extinction coefficient and particle diameter is obtained, which explains the extinction coefficient dependence on the size of the particle
