Asymmetric platinum film growth on SiO 2 microparticles The washed SiO 2 -wax colloidosomes were dispersed in an aqueous NH 4 OH solution (100mL, 0.6 v/v %) under gentle agitation using an orbital shaker. 360 µL of APTES was then added dropwise to this suspension, and left for 1 hour under continued shaking (350 RPM). The APTES-modified SiO 2 -wax colloidosomes were then collected by vacuum filtration on ashless filter paper and washed with copious amounts of distilled water (300 mL). The collected colloidosomes were then left to dry in a vacuum oven at 40 • C, weighed, then dispersed in 50 mL CHCl 3 and left stirring for 1 hour to dissolve the wax. The Janus-modified APTES-SiO 2 microparticles were then collected by vacuum filtration on a PTFE filter membrane (pore size 1.5 µm) by copious washing first by CHCl 3 (150 mL) then EtOH (50 mL). The particles were again dried in a vacuum oven and weighed. The yield of Janus particles was typically on the order of 50% (125 mg). Pt films were then asymmetrically grown on the Janus APTES-SiO 2 microparticles as described above.