Chinese scientists have folded DNA molecules in an origami-like process to make a nano "Trojan horse", which is thinner than 1/4000 of a hair and can release "killers" to fight cancer tumours.

Cancer cells need a lot of nutrition to multiply, but they do not produce nutrient substances, said lead researcher Nie Guangjun, from China's National Centre for Nanoscience and Technology (NCNST).

All the blood, oxygen and energy are conveyed to cancer cells through blood vessels, so many scientists are trying to create blocks on the blood vessels feeding tumours, Xinhua news agency reported.

Through precision control, researchers folded a single-strand DNA of a phage (a type of virus) into a rectangular sheet.

Then they put four "killers" -- molecules of thrombin (a clotting enzyme in blood plasma) -- on the sheet and rolled them up.

At the interface, "locks" made by fragments of nucleolin protein DNA were installed, forming a tube-shaped nano "Trojan horse" or nanorobot, which is 90 nanometers long and has a diameter of 19 nanometers.

After injection, the "Trojan horse" travels in blood vessels and only tumours have the "key" to open the "locks".

Once unlocked, the killer thrombin molecules are released, attracting platelets and fibrinogen protein to form a large thrombus, or clot, in the blood vessel within hours to cut off the blood supply and "starve" the tumour to death, Nie said.

The nanorobot can be cleared out of the body after it has finished its task.

Researchers have conducted controlled experiments on more than 200 mice with melanoma, breast cancer, ovarian cancer and primary lung cancer, and found the nanorobots are effective in strangling the tumours, Nie said.

In one experiment on eight mice with melanoma, the tumours in three mice totally disappeared. The average survival life of the mice was prolonged from 20.5 days to 45 days. No metastasis was found, Nie noted.