Chemotaxis of nonbiological colloidal rods

Chemotaxis is the movement of organisms toward or away from a chemical attractant or toxin by a biased random walk process. Here we describe the first experimental example of chemotaxis outside biological systems. Platinum-gold rods 2.0 mu m long exhibit directed movement toward higher hydrogen peroxide concentrations through active diffusion.'' Brownian dynamics simulations reveal that no temporal sensing'' algorithm, commonly attributed to bacteria, is necessary; rather, the observed chemotaxis can be explained by random walk physics in a gradient of the active diffusion coefficient.