STOCKHOLM - Americans Eric Betzig and William Moerner and German scientist Stefan Hell won the Nobel Prize in chemistry on Wednesday for developing new methods that let microscopes see finer details than they could before.

The three scientists were cited for "the development of super-resolved fluorescence microscopy," which the Royal Swedish Academy of Sciences said had bypassed the maximum resolution of traditional optical microscopes.

"Their ground-breaking work has brought optical microscopy into the nanodimension," the academy said.

Betzig, 54, works at the Howard Hughes Medfical Institute in Ashburn, Virginia. Hell, 51, is director at the Max Planck Institute for Biophysical Chemistry in Goettingen, Germany. Moerner, 61, is a professor at Stanford University in California.

Last year's chemistry prize went to three US-based scientists who developed powerful computer models that researchers use to understand complex chemical interactions and create new drugs.

This year's Nobel announcements started Monday with US-British scientist John O'Keefe splitting the medicine award with Norwegian couple May-Britt Moser and Edvard Moser for breakthroughs in brain cell research that could pave the way for a better understanding of diseases like Alzheimer's.

On Tuesday, Isamu Akasaki and Hiroshi Amano of Japan and Japanese-born US scientist Shuji Nakamura won physics award for the invention of blue light-emitting diodes _ a breakthrough that spurred the development of LED technology that can be used to light up homes and offices and the screens of mobile phones, computers and TVs.

The Nobel Prize in literature will be announced Thursday, followed by the Nobel Peace Prize on Friday and the economics prize on Monday.

The prizes are always handed out in ceremonies on Dec. 10, the date that prize founder Alfred Nobel died in 1896. A wealthy Swedish industrialist who invented dynamite, Nobel wanted his awards to honor those who "have conferred the greatest benefit to mankind," but gave only vague instructions on how to select winners.