We report the photodeposition of polymeric layers of nanometer scale thickness onto two nanoparticle substrates. This was accomplished by ultraviolet irradiation of a solution of functionalized diacetylene monomers in which the nanoparticles were suspended. Following photodeposition, the coated nanoparticles were analyzed using transmission electron microscopy and UV-visible spectroscopy. Highly regular polydiacetylene films with thicknesses from 2.5 - 25 nm were produced. The thickness measurements were facilitated by the attachment of small gold nanoparticles onto the surface of silica nanoparticle substrates prior to photodeposition, to provide contrast in the final TEM image. Deposition onto gold nanoshells was also demonstrated. Photodeposition onto these particles resulted in more individual coated particles. Furthermore, short irradiation times (approximately 5 minutes) yielded coated particles without the extra oligomeric contaminants usually found. This substantiates the idea that photodeposition occurs preferentially on a substrate material. UV-visible spectroscopy of the deposited films indicate that approximately 40% less conjugation is present relative to macroscopic polydiacetylene thin films grown with the same approach. This process yields a unique `nanolaminate' coating which may be useful in the modification of the physical, chemical, or optical properties of nanoparticles.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.