Organisation of nanoparticles on structurally well-defined templates is a first step towards creating nanomachines. In this respect, nucleic acids are ideal structural templates and a variety of secondary structures realizable from DNA/RNA - e.g., duplexes, hairpins, triplexes, cruciforms, tetraplexes can be exploited to engineer nanoparticle organization at will. We have used oligonucleotides and their analogues such as phosphorothioates and peptide nucleic acids to electrostatically encapsulate cationic-capped gold nanoparticles. This article describes synthesis and characterization of DNA/PNA-gold nanoparticle composites using TEM and UV-T-m techniques. These types of assemblies may have potential for creating nanowires and lithographic circuits. (C) 2004 Elsevier B.V. All rights reserved.