Metallic nanoparticles have been the subject of intense research recently because of their catalytic properties, which may differ considerably from the bulk metal. As the free nanoparticles tend to aggregate and are difficult to handle in catalytic applications, colloidal carrier systems have been developed that encapsulate and stabilize the particles. More recently, so-called smart carrier systems, such as thermosensitive microgels, [8] have become the focus of research. These hybrids react on external stimuli and allow the catalytic properties to be altered accordingly. Thus, thermosensitive polystyrene (PS)-poly(N-isopropylacrylamide) (PNIPA) core-shell microgels were applied as the active nanoreactor for the immobilization of metal nanoparticles. [10] The catalytic activity of immobilized metal nanoparticles can be tuned by the swelling and shrinking of the microgels. [11] Liz-Marzµn et al. have developed a Au-PNIPA core-shell colloidal system. They found that the thermoresponsive PNIPA shell with limited cross-linking allows for particularly efficient control of the catalysis of encapsulated Au nanoparticles. Recently, yolk-shell structures that consist of a single metal nanoparticle within an inorganic [15] or polymeric shell have become the subject of intense research. These systems can be used to tune the catalytic activity of the enclosed nanoparticle by a suitable architecture of the shell. Yolk-shell structures have the clear advantages in that individual metal nanoparticles are enclosed in a compartment that prevents aggregation with other nanoparticles. Furthermore, the embedded gold nanoparticle has a free surface that