The one-step electrostatic complexation, reduction of aqueous chloroplatinate ions, and capping of the platinum nanoparticles thus formed by hexadecylaniline Langmuir monolayers is described. The capping of the platinum nanoparticles formed spontaneously at the air-water interface by hexadecylaniline enables their facile transfer as multilayers onto suitable solid substrates by the Langmuir-Blodgett technique. The real-time reduction of the aqueous chloroplatinate ions at the air-water interface was followed by measurement of the pressure-area isotherms. while the multilayer Langmuir-Blodgett films were characterized by quartz crystal microgravimetry, transmission electron microscopy, electron diffraction, and X-ray photoemission spectroscopy. (C) 2003 Elsevier Inc. All rights reserved.