Controlling the size of electrostatically self-assembled nanoparticles with cyclodextrin as external trigger

Abstract

This study shows how electrostatic self-assembly of polyelectrolytes and organic counterions can be combined with cyclodextrin host–guest chemistry into a novel route to size-controllable supramolecular nanoparticles in aqueous solution. Nanoparticles are formed from fourth generation polyamidoamine dendrimers (PAMAM G4) as positively charged macroions and an excess of the oppositely charged anionic diazo dye Acid Yellow 38 (Ay38), yielding negatively charged supramolecular particles with hydrodynamic radii of 30–60 nm. Stepwise complexation of the dye by α-cyclodextrin leads to a decreasing charge density and thereby caused stepwise size increase up to particles with a hydrodynamic radius of 240 nm. Dynamic light scattering and ζ-potential measurements were used to elucidate assembly size and stabilization and isothermal titration calorimetry to determine association stoichiometry, enthalpies and equilibrium constants.