Self-organized tubular structures as platforms for quantum dots.

The combination of top-down and bottom-up approaches offers great opportunities for the production of complex materials and devices. We demonstrate this approach by incorporating luminescent CdSe-ZnS nanoparticles into macroscopic tube structures that form as the result of externally controlled self-organization. The 1-2 mm wide hollow tubes consist of silica-supported zinc oxide/hydroxide and are formed by controlled injection of aqueous zinc sulfate into a sodium silicate solution. The primary growth region at the top of the tube is pinned to a robotic arm that moves upward at constant speed. Dispersed within the injected zinc solution are 3.4 nm CdSe-ZnS quantum dots (QDs) capped by DHLA-PEG-OCH3 ligands. Fluorescence measurements of the washed and dried tubes reveal the presence of trapped QDs at an estimated number density of 10(10) QDs per millimeter of tube length. The successful inclusion of the nanoparticles is further supported by electron microscopy and energy dispersive X-ray spectroscopy, with the latter suggesting a nearly homogeneous QD distribution across the tube wall. Exposure of the samples to copper sulfate solution induces quenching of about 90% of the tubes' fluorescence intensity. This quenching shows that the large majority of the QDs is chemically accessible within the microporous, about 15-μm-wide tube wall. We suggest possible applications of such QD-hosting tube systems as convenient sensors in microfluidic and related applications.