Effect of Picosecond Postirradiation on Colloidal Suspensions of Differently Capped AuNPs

Fifth generation ethylendiamine-core poly(amidoamine) (PAMAM-G5) and poly(ethyleneimine) capped gold nanopartides were prepared by picosecond laser ablation in water, by using the fundamental wavelength of a picosecond Nd:YAG laser. The role of PAMAM-G5 inner cavities in the processes of photofragmentation of the nanoparticles by postirradiation with the second or third harmonic from the same laser is assessed through comparison of the experimental results obtained with the two stabilizers and the shot-by-shot theoretical modeling of the photo-bleaching process. We also show how thorough bleaching of the suspensions by postirradiation with 532 nm causes a strong increase of their fluorescence emission. Such fluorescence, which cannot be attributed to new fluorescent species, such as gold quantum dots, is due to a strong enhancement of the Intrinsic emission bands of both stabilizers and is related to formation of gold subnanometer fragments and their subsequent interactions with the molecular compounds.