Engineers from the University of California San Diego have demonstrated a magnetically propelled, fish-like nano-swimmer that could be used to carry drugs to specific sites of the body. The artificial fish are 100 times smaller than grains of sand, and are made from gold and nickel segments linked by silver hinges. The two outer gold segments act as the head and tail fin, while the two inner nickel segments form the body. When an oscillating magnetic field is applied, the magnetic nickel parts move from side to side. This swings the head and the tail, creating a motion that pushes the nanofish forward. Speed and direction can be controlled by altering the strength and orientation of the magnetic field.