UV-Vis-NIR Laser Desorption/Ionization of Synthetic Polymers Assisted by Gold Nanospheres,Nanorods and Nanostars

The laser desorption/ionization (LDI) assisted by gold nanospheres, nanorods and nanostars has been investigated. Laser fluence thresholds for the appearance of cationized adducts of a polydispersed polyether standard (polyethylenglycol PEG600) have been determined at the near ultraviolet–visible–near infrared wavelengths delivered by a Nd:YAG laser (266, 355, 532, 1,064 nm). The results demonstrate the efficiency of surface plasmon excitation to assist laser desorption/ionizaton at laser wavelengths extending to the visible and near infrared, with advantages with respect to conventional LDI techniques using ultraviolet wavelengths. A close correlation is found between the optical absorbance of the nanoparticles and the LDI thresholds, although for the nanospheres plasmonic excitation in the visible appears to be more efficient than non-plasmonic excitation at shorter UV wavelengths. The recorded molecular weight distributions for the PEG600 standard show that the LDI process tends to be less efficient for the heavier components of the polymer mixture, presumably as a consequence of their stronger bonding to the nanoparticle substrate. The role of the coating agent of the nanoparticles in the observed LDI behavior is discussed.