Canadian researchers have created self propelled "nanobots" by coupling live, swimming bacteria to nano-sized beads. As Technology Review explains:
A team led by École Polytechnique de Montréal computer engineering professor Sylvain Martel ... is the first to show that such hybrids can be steered through the body using magnetic resonance imaging (MRI).
To do this, Martel used bacteria that naturally contain magnetic particles. In nature, these particles help the bacteria navigate toward deeper water, away from oxygen. "Those nanoparticles form a chain a bit like a magnetic compass needle," says Martel. But by changing the surrounding magnetic field using an extended set-up coupled to an MRI machine, Martel and his colleagues were able to make the bacteria propel themselves in any direction they wanted.
The bacteria swim using tiny corkscrewlike tails, or flagella, and these particular bacteria are faster and stronger than most, says Martel. What's more, they are just two microns in diameter--small enough to fit through the smallest blood vessels in the human body. The team treated the polymer beads roughly 150 nanometers in size with antibodies so that the bacteria would attach to them. Ultimately, the researchers plan to modify the beads so that they also carry cancer-killing drugs.