280 µL solutions of the Fe 2 O 3 -TiO 2 -SiO 2 in fuel-rich aqueous conditions (H 2 O 2 , 3 % v/v, diluted from a stock 30 % v/v solution (Acros Organics)) were prepared in a microscopy cell as previously described, and videos were taken at 10 FPS. To activate the TiO 2 photocatalyst and induce swimming, particles were illuminated with UV (340 nm), using a Lumencor SPECTRA X light engine as the excitation source through the objective (epifluorescence).