Light-responsive aggregation of β-cyclodextrin covered silica nanoparticles

In this article, we report a tight-responsive supramolecular system based on the host guest interaction of beta-cyclodextrin covered silica nanoparticles and a bifunctional, noncovalent azobenzene linker in dilute aqueous solution. beta-Cyclodextrin was immobilized onto silica nanoparticles either by nucleophilic substitution or by thiol-ene click chemistry. Azobenzene has two isomers which can be converted into each other by alternating irradiation with visible light (lambda = 465 nm) and UV light (lambda = 350 nm). When using visible light, the trans isomer of the azobenzene moieties on the linker bind to the beta-cyclodextrin cavities on the nanoparticle surface leading to aggregation of the nanoparticles. The aggregation is reversible, since irradiation with UV light leads to the formation of the cis isomer of the azobenzene linker, dissociation of the azobenzene and the cyclodextrin, and subsequent dispersion of the nanoparticles. The light-responsive supramolecular system is investigated by using optical density measurements (OD600), DLS and TEM measurements.