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Nanotechnology has been harnessed to kill cancer cells without harming healthy tissue.
The technique works by inserting microscopic synthetic rods called carbon nanotubules into cancer cells.
When the rods are exposed to near-infra red light from a laser they heat up, killing the cell, while cells without rods are left unscathed.
Details of the Stanford University work are published by Proceedings of the National Academy of Sciences.
Researcher Dr Hongjie Dai said: "One of the longstanding problems in medicine is how to cure cancer without harming normal body tissue.
"Standard chemotherapy destroys cancer cells and normal cells alike.
"That's why patients often lose their hair and suffer numerous other side effects.
"For us, the Holy Grail would be finding a way to selectively kill cancer cells and not damage healthy ones."
Many in cell
The carbon nanotubules used by the Stanford team are only half the width of a DNA molecule, and thousands can easily fit inside a typical cell.
Under normal circumstances near-infra red light passes through the body harmlessly.
But the Stanford team found that if they placed a solution of carbon nanotubules under a near-infra red laser beam, the solution heated up to about 70C in two minutes.
They then placed the tubules inside cells, and found they were quickly destroyed by the heat generated by the laser beam.
Dr Dai said: "It's actually quite simple and amazing. We're using an intrinsic property of nanotubes to develop a weapon that kills cancer."
The next step was to find a way to introduce the nantubules into cancer cells, but not healthy cells.
The researchers did this by taking advantage of the fact that, unlike normal cells, the surface of cancer cells is covered with receptors for a vitamin known as folate.
They coated the nanotubules with folate molecules, making it easy for them to pass into cancer cells, but unable to bind with their healthy cousins.
Exposure to the laser duly killed off the diseased cells, but left the healthy ones untouched.
Refined technique
The researchers believe it should be possible to refine the technique still further, for instance by attaching an antibody to a nanotubule to target a particular kind of cancer cell.
They have already started work on tailoring the technique to target lymphoma in mice.
Dr Emma Knight, of the charity Cancer Research UK, said: "Nanotechnology has a lot to offer biomedical science, and the results of this paper suggest yet another way in which it may help in the fight against cancer.
"However, this work is still at a very early stage. The researchers have shown that near-infra red light can cause nanotubes to produce heat that can kill cancer cells.
"But their work so far has focused on cells that have been grown in culture in the laboratory.
"Further research will be crucial to see whether these effects can be reproduced in the more complex environment of a tumour and, ultimately, the human body."
