According to a report in the journal New Scientist, the new method of delivery involves enclosing the drug in special polymer capsules that are full of gold nanoparticles and attached to tumour-seeking antibodies.

When these capsules are injected into the bloodstream the capsules will concentrate inside tumours. After enough capsules have gathered in the target region, a pulse from a "near-infrared" laser will melt the gold. As a result the plastic capsules are ruptured and the contents released in a specific location.

The capsules are invisible to the eye without the aid of a powerful electron microscope. Researchers make them by repeatedly adding the polymer to a suspension of drug particles that are roughly one thousandth of a millimetre wide until the polymer forms tiny spheres containing the drug payload. Gold particles that are six nanometers, or six billionths of a metre in diameter, are then added to the mix, together with the antibodies which will target the tumour and a lipid polymer that forms an outer layer.

In laboratory tests the capsules were ruptured by a ten nanosecond pulse from a near-infrared laser.

Because of the nanostructure of the gold particles, the pulse is enough to melt them at a much lower temperature than normal, without damaging the precious drug payload.

The report said: "In clinical use, the laser would be able to penetrate a few millimetres of tissue. It could be shone through the skin, or be beamed inside the body through an endoscope."

Dr Caruso said he believed the key innovation of the research had been in making the particles react to a laser that is harmless to the body.

He told New Scientist: "The [amount of] infrared energy needed to rupture the capsules is well within safety limits and is way below that used to remove tattoos."

At present, chemotherapy is what is known as a systemic therapy, meaning the drugs affect the whole body by going through the bloodstream.

The treatment is effective against cancer cells because the drugs interfere with rapidly dividing cells. However, chemotherapy has side-effects because cancer cells are not the only rapidly dividing cells in the body. The treatment's systemic nature means the drugs have access to all such cells, even those necessary for the body's continued good functioning.

Nanoscale drug delivery could make the prospect of chemotherapy much less worrying to many cancer sufferers.

Is this still basically theoretical, or they in any phase of trials yet?