Isolated single-walled carbon nanotubes in a gel as a molecular reservoir and its application to controlled drug release triggered by near-IR laser irradiation

We describe the preparation of a single-walled carbon nanotube-based molecular container with a stimuli responsible releasable functionality. First, single-walled carbon nanotube (SWNT)-embedded composite gels are synthesized by the gelation of three different acrylamide derivatives including N-isopropylacrylamide (NIPAM), acrylamide and N,N-dimethylacrylamide (DMAAM) in the presence of individually dissolved SWNTs aided by aqueous micelles of sodium dodecylbenzenesulfonic acid (SDBS), and then the SDBS molecules were removed from the gels. The SWNTs remained isolated even after the removal of SDBS in the gel of NIPAM and copolymer gel of NIPAM and DMAAM, while the SWNTs dispersed in the gels of acrylamide and DMAAM formed bundle structures. The SWNT surfaces having large surface areas in the gel were thus obtained, then utilized as a scaffold for the adsorption of small hydrophilic molecules, such as an antineoplastic agent, doxorubicin hydrochloride (DOX). The SWNTs in the gel of NIPAM served as a molecular container to effectively hold the DOX molecules in basic aqueous media, and by lowering the pH, the DOX molecules on the SWNT surfaces were released into the bulk aqueous solution. Moreover, we have succeeded in the laser light-driven quick release of DOX molecules from the composite gel of NIPAM and DMAAM using a photothermal conversion effect of the SWNTs.