Catch and Release Chemotaxis

Catch and release chemotaxis was studied by using a self-propelled 6-methylcoumarin (6-MC) disk floating on water. A tablet of Na3PO4 placed at the bottom of the water phase acted as a chemical stimulus. The repetition of catch and release chemotaxis, that is, the alternating inversion of the spatial gradient of surface tension, was realized using one 6-MC disk and one Na3PO4 tablet. Alternating catch and release chemotaxis was observed using two 6-MC disks and one Na3PO4 tablet. The mechanism of catch and release chemotaxis is discussed in relation to the change in the surface tension of the 6-MC aqueous phase following the addition of Na3PO4 as the driving force, the spatial concentration gradient of the base dissolved from the tablet in the water phase, and the chemical reaction between 6-MC and OH-. Understanding this type of chemotaxis system can elucidate the chemotaxis behaviors of living organisms.