The polymer-modified colloidosomes were then washed thoroughly in deionized water before redispersion in a phosphate-buffered saline (PBS) pH 7.0 suspension containing the functional metal-oxide nanoparticles (TiO 2 P-25 (Sigma Aldrich, 21 nm primary size), Fe 2 O 3 (Sigma Aldrich, ¡50 nm primary size)). After gentle mixing overnight, the nanoparticlefunctionalised colloidosomes were collected by filtration and the wax was finally removed with chloroform to obtain the asymmetrically modified Janus microswimmers.