U.S. medical researchers are hoping that using magnetism and nanotechnology to harness a biological control system could become a noninvasive way to treat diseases.

The "nanomagnetic cellular switch" enabled the researchers to control living cells through magnetic forces rather than chemicals or hormones, said lead researcher Dr. Don Ingber, from Children's Hospital Boston.

"We can control it at will."

The research might be used to deliver drugs, detect problems or control processes such as heart rhythms and muscle contractions, they said in a release Wednesday.

The researchers got tiny beads 30 nanometres in diameter to bind to receptor molecules on the cell surface. When they turned on a magnetic field, the beads themselves become magnetized and pulled together, pulling the receptors with them.

"They became like little bar magnets," Ingber said.

When the receptors cluster because of the magnetic attraction, they become activated, and trigger the biochemical signals that influence cell functions.

It's the same process that occurs when doctors administer a hormone, but that is much slower because it doesn't start until the hormone gets enough receptors to cluster, and takes longer to stop, as the hormone slowly washes out of the cell, he said. Now, "we could just use a magnet to go on-off, on-off."

The researchers demonstrated the process using immune system mast cells, stimulating a flow of calcium into the cells after the beads were bound to cell receptors and exposed to a magnetic field. There was no effect when the magnetic field was used without the beads.

A calcium influx is a signal used by nerve cells to start an impulse along a nerve fibre, and by heart and muscle cells to stimulate contractions.

The 30-nanometre beads are too tiny to imagine.

"To give a sense of scale, one nanometre is to a metre [about a yard] as one blueberry is to the diameter of the Earth," the release said.

Inger worked with Robert Mannix from the Children's Hospital and physicist Mara Prentiss of Harvard University.

The study is in the January issue of Nature Nanotechnology.