Fig. 7. (a) Asymmetric light-emitting electrochemical swimmer. Simultaneous reduction of H₂O at the cathodic pole (bottom of the bead) and oxidation of ECL reagents at the anodic pole (top of the bead) induce both motion and light emission from the bead in a glass capillary. P corresponds to a side product of the TPrA radicals formed during the ECL process. (b) Levitation of a light-emitting GC bead. Series of optical images showing a GC bead emitting ECL at different times during its motion. The bead was placed in a U-shaped cell, filled with 100 mm PBS buffer containing 0.5 mm Ru(bpy)₃²⁺, 100 mm TPrA, and a few drops of the surfactant. It was exposed to an external electric field of 25.5 V cm⁻¹. The left image was taken under white light and the other images were taken in the dark. Inset: plot showing the change in height h of the bead as a function of time t. Reproduced from ref. 76 with permission from Wiley-VCH, copyright [2012].