Photonic crystal fibers have been the subject of several studies for potential application in areas such as sensing, nonlinear optics, telecommunication and nanophotonics. Many applications are enabled by the possibility of selectively inserting gases, liquids, polymers and colloids into the internal microstructure, which results in efficient interaction with the guided light, allowing for the development of, e.g., sensitive chemical sensors also, the insertion of materials can be exploited to modify waveguide characteristics such as modal field distributions, the nonlinear coefficient and the chromatic dispersion. Experimentally, the insertion of liquids is particularly straightforward and enables many of the envisaged studies. However, evaporation is an important limiting issue, which ultimately prevents the realization long-term practical applications. Also, in some cases contact of the liquid with the external environment may degrade its properties. To address these issues, we experimentally demonstrate a new technique to selectively seal a liquid-filled hole of a photonic crystal fiber. The characteristics of the sealed fibers remained stable for at least a few weeks. Two experiments were, then, carried out to demonstrate the potential of the technique. In the first experiment, a water-core photonic crystal fiber was used for supercontinuum generation, with the generated spectrum not showing degradation over time. In the second experiment, a colloid of CdSe nanoparticles was inserted into the core of a fiber and stable photoluminescence was observed.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.