Researchers have developed a device that uses 55,000 microscopic “pens” to write patterns with nanoscale features–and could even use biological molecules such as DNA or proteins as “ink.” The tool could someday lead to powerful new diagnostic tests and cancer therapies. Created by Northwestern University chemist Chad ­Mirkin, the device is a leap forward from earlier versions that had just one pen (see “Nanobiotech Makes the Diagnosis,” May 2002). The greater numbers translate to added speed, which could allow researchers to run thousands of experiments at once. For example, they could print nearly infinite combinations of proteins and test their effects on cells, a process that could lead to new drugs. The new nano machine is fast: as a demonstration, ­Mirkin printed 55,000 images of a nickel in an area smaller than a dime–and did it in less than half an hour.