Zinc oxide (ZnO) nanoparticles were prepared in neat deionized water by laser ablation with various ablation times (10-40 min), fluences (50-130 mJ/pulse), and wavelengths (1064, 532, and 355 nm). The size and shape of the nanoparticles were affected only slightly by the ablation time and fluence at a wavelength of 1064 nm, which was explained by a dynamic formation mechanism with surface charge effects. The nanoparticles formed by ablation at 355 nm had a distinctive wire-shape with a small diameter, which was attributed to a continuous fragmentation and formation mechanism. (C) 2011 Elsevier B.V. All rights reserved.