Two Americans and a German won the 2014 Nobel Prize for Chemistry on Wednesday for laying the foundations of an ultra-powerful microscope that allows the study of tissue at the molecular level.

The tool has revolutionized research into disease and drug design, the Nobel jury said, as it lauded Americans Eric Betzig and William Moerner and ­Germany's Stefan Hell.

"Their ground-breaking work has brought optical ­microscopy into the nano-­dimension," it said.

"Today, nanoscopy is used worldwide and new ­knowledge of the greatest benefit to ­mankind is produced on a daily ­basis."

Working separately, the trio overcame a limit set in 1873 by microscopist Ernst Abbe, who said the resolution of an image would never be better than around 200 nanometers (200 billionths of a meter), which is half the wavelength of light.

Because of this so-called diffraction limit, it was thought that the inner workings of a cell would never be clearly observed, inhibiting our understanding of how cells function, reproduce or become infected.

The basis of the laureates' work, dating back to pioneering research by Hell in the 1990s, adds fluorescent molecules to a sample to be studied.

A laser beam is then directed at specific molecules on the fringes of the area of interest, so that they glow. The fluorescence is then filtered out so that, in the centre of the image, precise structures as small as 20 nanometers come into view.

"It's childish, but it still gives me great pleasure to see high-res pictures everyone told me would be impossible," Hell said in a 2009 interview with the British science journal Nature.

Medicine and biology have been the big winners from developments in ­nanoscopy.

The race for the Nobel peace prize, to be announced Friday, has rarely been so ­unpredictable, experts say, with the pope and Edward Snowden tipped as possible winners.

Snowden, the former intelligence analyst who revealed the extent of US global spying, was one of the joint winners of the "alternative Nobel peace prize" last month.

A hero to some and a traitor to others, he would be a highly controversial choice for the 878,000 euro ($1.11 million) award.

Pakistani girls' education campaigner Malala Yousafzai is also said to be in the running along with Pope Francis  and a Japanese pacifist group.