A team of scientists in South Korea has used a sol-gel process to fabricate color-tunable silica nanotubes that incorporate functional laser dyes. The investigators suggest that the one-dimensional structures may form the basis of new nanoscale emitters, with potential applications in optical sensing and displays.A sol-gel technique enables the synthesis of nanostructures loaded with laser dyes. Confocal laser scanning microscopy, performed at an excitation wavelength of 360 nm, suggests that the dye is covalently attached to the interior wall of the nanotubes (A). Electron microscope images show the tubular construction of the structures (B and C). Energy-dispersive x-ray spectroscopy reveals peaks for carbon, oxygen and silicon in the spectra of a nanotube loaded with anthracene (D). Courtesy of Jong Hwa Jung, Korea Basic Science Institute. The researchers from Korea Basic Science Institute and Korea Advanced Institute of Science and Technology, both in Taejon; Kangwon National University in Chun-cheon; and Chonbuk National University in Chonju, made nanotubes loaded with coumarin or anthracene dye. A cylindrical cholesterol-based gelator served as a template to which the dye anchored and around which the silica formed. A mixture of dye and tetraethoxysilane yielded tubes over a period of five days at room temperature.Photoluminescence measurements revealed that the response of the structures differed with their environment. When excited with 280-nm radiation from a Liconix HeCd laser, coumarin-loaded tubes produced 486-nm light when they were suspended in ethanol and 482-nm light when they were in the solid state. Anthracene-loaded tubes in ethanol and the solid state produced 465- and 483-nm light, respectively. The investigators attribute the shift in the response to an increased contribution from the nanotubes in the solid state.Jong Hwa Jung of Korea Basic Science Institute predicted that the synthesis technique will enable the production of luminescent nanostructures of various shapes and sizes. Given the proper gelator to serve as the desired template, he said, it should be possible to fabri-cate linear, helical, bundled, multilayered cigarlike and vesicular loaded structures.Potential applications of the loaded silica nanotubes are being considered, Jung said. With the correct choice of dyes, for example, red, green and blue tubes could be synthesized as nanosize emitters and assembled to produce a full-color display.