Formation of Self-Assembled Au Nanoparticles and the Study of Their Optical Properties by Steady-State and Time-Resolved Spectroscopies

Here, we report the formation of self-assembled Au nanoparticles using different capping agents and study their optical properties by steady-state and time-resolved spectroscopies. The generation of a second surface plasmon band at 680 nm, with increasing concentration of the capping agent, reveals the formation of the self-assembled structure of Au nanoparticles, which is further confirmed by TEM and time-resolved anisotropy studies. A mechanism for self-assembled Au nanoparticles is also proposed. Quenching efficiency of isolated Au nanoparticles is different from assembled Au nanoparticles, which varies with capping agent concentrations. The calculated energy transfer efficiencies from Rhodamine 6G to Au nanoparticles are 35.6, 21.7, and 10.1%, and the measured distances between the dye and Au nanoparticles are 91.7, 108.9, and 136.5 Å for 50 μM, 75 μM, and 125 μM concentrations of 3-mercaptopropionic acid, respectively, which are very nicely matched with the thickness of molecular coverage on Au nanoparticles.