Multimedia Gallery - Particle motion driven by light provides a theory for independent movement of nano-machines.

Two different particles engage in phototaxis predator-prey movement.

April 22, 2009

Particle motion driven by light provides a theory for independent movement of nano-machines.

The study of bacteria offers some intriguing theories for building autonomous nano-motors. One theory involves phototaxis--particle motion driven by light in which particles move towards or away from the region of highest light intensity. Movement depends on the nature of the ions given off by a lighted particle and the charge of the particle. The phenomenon can lead to biomimetic cooperative behavior, such as one in which some particles act as "predators" and others as "prey," very much like white blood cells chasing down a bacterium. The design of "smart" autonomous nano-robots could take on similar characteristics, moving independently in a needed direction by harvesting energy from light, glucose or other abundant fuels in biological or organic systems. Here, two different particles engage in phototaxis "predator-prey" movement. Dark silver chloride particles when stimulated by UV light emit positively charged ions. These ions propel the movement of the silver chloride particles, but they also cause attraction of the lighter colored silica particles. Consequently, the "prey" particles are eventually surrounded by "predators." The silver chloride particles are shown first in a neutral state, and then they are photographed after 20 seconds of exposure to UV light and again after 85 seconds of exposure. The exposure causes them to be surrounded by silica particles that are attracted by the ions. The results cause researchers to hypothesize that nano-engines using similar technologies may not be that far away.

Credit: Michael E. Ibele, Thomas E. Mallouk, and Ayusman Sen, Angew. Chem., in press

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