Stock in Nanogen Inc. soared 51 percent Wednesday after the San Diego biotechnology company announced that it had received what it described as a key U.S. patent in the emerging science of nanotechnology.

Nanogen stock rose $1.95 to close at $5.74.

However, a prominent biotechnology observer advised caution in evaluating the company's prospects.

The Nanogen patent, No. 6,652,808, covers methods of assembling DNA, the carrier of heredity, to create various types of electronic parts, such as very small, high-capacity data storage devices, light sources and biosensors.

Nanotechnology is the field of manufacturing at the molecular or atomic level. Its boldest advocates envision molecular machines swarming into cells to repair genetic damage, ultra-powerful miniature computers and other remarkable feats.

In Washington on Wednesday, President Bush signed a bill to spend $3.7 billion for nanotechnology research. The bill funds programs to find ways nanotechnology can detect and treat disease, monitor the environment, and produce and store energy.

At present, however, nanotechnology exists almost entirely in theory. While scientists such as nanotech pioneer Eric Drexler have described how molecular machines could function, the bottleneck has been in making these machines in the first place.

The Nanogen patent says it addresses that issue by describing how an electric field can be used to select the desired pieces of DNA and assemble them in the desired order.

John McCamant, editor of the Berkeley-based Medical Technology Stock Letter, said the Nanogen patent didn't justify the buying enthusiasm, because often technological advances in biotech fail to generate profitable products. For example, he said, most biotech companies that worked in the field of genomics failed to make money with he technology.

"I advice investors to be particular careful … and probably wait so this company shows us how it's going to deliver on some of this promise," McCamant said.

Nanogen's chairman and chief executive, Howard Birndorf, co-founded San Diego's first biotechnology company, Hybritech, about 25 years ago. The company was sold for $400 million in 1986.

Birndorf went on to co-found other successful biotech companies, including Idec Pharmaceuticals Corp. (now Biogen Idec), Ligand Pharmaceuticals Inc. and Gen-Probe Inc., before founding Nanogen in 1993.

The Associated Press contributed to this story.

Contact staff writer Bradley J. Fikes at (760) 739-6641 or bfikes@nctimes.com.