gained Monday after the developer of diagnostic products said it was issued a patent for its apparatus for active biological sample preparation.

The San Diego-based company said the Patent and Trademark Office issued U.S. Patent No. 6,824,740, the company's 81st in the U.S.

The company said the patent allows for an integrated system in which some or all of the processes involved in sample preparation are performed together.

"The new patent expands Nanogen's intellectual property portfolio covering technologies involved in development of sample-to-answer molecular diagnostics," the company said.

Shares rose 48 cents, or 7.8%, to $6.46 in unusually heavy trading for the stock. Some 3.7 million shares changed hands, more than three times the daily average of almost 1.2 million shares.