Platinum Nanoparticles Prepared by Laser Ablation in Aqueous Solutions: Fabrication and Application to Laser Desorption Ionization

Abstract

Aqueous suspensions of platinum colloidal nanoparticles of varying size and polydispersity have been produced by ablation of a platinum target with a nanosecond Q-switched Nd:YAG laser. Several laser wavelengths (1064, 532, and 266 nm) and stabilizing agents (citrate and polymers PEG, PVA, and PVP) were employed. Laser ablation with the infrared and visible wavelengths leads to spherical amorphous nanoparticles with a bimodal distribution of diameters, featuring a global maximum in the range 5–10 nm and a shoulder extending to 25 nm. Such bimodal distributions plausibly arise from thermal and explosive vaporization mechanisms occurring in different time scales, as proposed in earlier studies. Ultraviolet ablation of Pt at 266 nm, reported here for the first time, produces crystalline nanoparticles of small size (1–4 nm diameter), with a weak onset of larger particles (6–8 nm). The ablation at 266 nm also produced an appreciable yield of large rodlike particles of size ∼10 × 70 nm2, especially in the presence of PEG and PVA. The Pt nanoparticles served to fabricate films capable of assisting the laser desorption ionization (LDI) of a model peptide. The best analytical performance for LDI mass spectrometric detection was obtained with Pt nanoparticles surface-functionalized with citrate and PVA.