Magnetic nanoparticles can be used to control human behavior.

From PopSci:

Researchers in Buffalo are bringing us a step closer to being controlled by machines. Or magnetized nanoparticles, at least: Heated magnetic nanoparticles targeted to cell membranes could control your behavior, according to a new paper in Nature Nanotechnology.

The researchers, led by University of Buffalo physics professor Arnd Pralle, used magnetic fields to activate neurons in a cell culture and steer the movement of nematode worms.

The findings could lead to cancer treatments that remotely manipulate cells in certain tissues, or diabetes therapies that remotely stimulate pancreatic cells to release insulin, according to the University of Buffalo.

[...] Because the cells are not harmed, the method can be used in living animals, which opens the door for specialized pharmaceuticals or therapies. It can also illuminate the signaling networks that control animal behavior, Pralle says.