We report on a facile and reliable preparation of polypyrrole vessel structures modified with gold nanoparticles that are able to encapsulate organic molecules of biological importance. The polymer is coated onto the surface of aqueous droplets through photopolymerization of the monomer. When gold nanoparticles and/or biomolecules are contained in the droplets, these species become incorporated within the formed polymer microvessels. Herein, we provide thorough physicochemical characterization of the polymer structures including electron and optical microscopy, spectroscopy (steady state and time-resolved fluorescence, XPS, XRF) and other experimental techniques. Polymer microvessels are promising as smart drug carriers for new experimental therapies. As model drugs we use mRNA cap analogs which are nucleotide-derived compounds that have been shown to be potential anti-cancer agents. We demonstrate that embedding the metallic nanoparticles within the microvessels provides usefully high contrast in micro-computed tomography (microCT) which is promising from the standpoint of monitoring the fate of administered drug carriers inside the body. Moreover, our in vivo studies on rats demonstrate that intravenous administration of the microvessels does not evoke acute toxicity or death of the animals. (C) 2014 Elsevier Ltd. All rights reserved.