Nanotechnology - the science of tiny particles scientists have come up with a fast-acting treatment for impotence that could rival Viagra. According to researchers the drug's minute particles can be absorbed directly through the skin, causing a sexual response within minutes. The treatment has so far only been tested in animals but the researchers behind it say the same approach could also benefit humans.

Popular erection providing drugs like Cialis, Viagra and Levitra are taken orally, taking time to digest and have an effect. The nanoparticle approach, by contrast, worked in less than 10 minutes and its effects seem to be limited to the relevant parts of the body, according to the researchers.

Kelvin Davies of the Albert Einstein College of Medicine in New York, who oversaw the research, said the results showed the potential for "nano-medicines". He said the nanoparticles "can facilitate transport of erectogenic agents. It localises the therapeutic impact without the potential consequences due to systemic absorption". In the study, to be published today at the annual meeting of the American Urological Association, Davies and his colleagues loaded the nanoparticles with nitric oxide, a chemical that occurs naturally in the body where it makes blood vessels expand and fill with blood.

They applied the particles to the skin of rats bred to suffer from impotence. They observed a rapid and strong response. The potential market for such drugs is extensive. Viagra has become one of the world's most popular medicines with about 40m pills prescribed in Britain alone since its launch in 1998.