This isn’t the first time researchers have developed biomimicking particles, but self-propulsion has caused a problem in the past. To make these particles, the researchers wrapped hematite, an iron-based mineral, in a thin, pale polymer. Under regular conditions, the particles simply float when they’re in a solution. But if the particles are exposed to blue light, the hematite conducts electricity and, in a bath of hydrogen peroxide, starts splitting the oxygen from the hydrogen. The result is a chemical gradient on which the particle can flow, irrelevant of the direction the solution is moving, called persistent random walk. In the natural world, parasites and marine plankton move in the same way through the body and ocean respectively.