Carboxyl-functionalized cross linked polymeric nanocapsules (PAA-CPS) with pH-responsive poly(acrylic acid) (PAA) brushes on the inner wall of the crosslinked polystyrene (CPS) shells have been prepared by the template-polymerization approach via combination of surface-initiated atom transfer radical polymerization (SI-ATRP) and ultraviolet-irradiated crosslinking techniques. The hollow structure of the crosslinked nanocapsules with an inner diameter of about 30-40 nm was confirmed by transmission electron microscopy (TEM). The adsorption experiments showed that the PAA-CPS nanocapsules possess a higher adsorption capacity towards the basic dye methylene blue (MB) than the PtBA-CPS nanocapsules. Furthermore, the MB-loaded PAA-CPS nanocapsules release the dye more rapidly in acidic medium than in a neutral medium. (C) 2010 Elsevier Ltd. All rights reserved.