Silicon Forests

In fact the success of MEMS may depend more on engineers being able to think up new uses for them than it does on the skill of microfabrication labs. Kurt Petersen, widely considered one of the fathers of MEMS because of a seminal paper he wrote in 1980 at IBM Research in San Jose, Calif., is, for one, focusing his energy on Cepheid, which he co-founded three years ago in Sunnyvale, Calif. “Our role in life is DNA analysis,” says Petersen. And he’s convinced MEMS are going to prove useful.

One of the most time-consuming and least automated tasks of DNA analysis is the preparation of specimens-extracting, concentrating and purifying the genetic material so that it can be copied and sequenced. “People have not been able to extract and purify DNA on a microscale,” points out Petersen. Enter MEMS. Using a technique called deep reactive ion etching, in which ions chew straight down into exposed areas of a silicon wafer (as opposed to the surface micromachining used to make Texas Instruments’ tiny micromirrors and Analog Devices’ accelerometers), Petersen and his colleagues have created microfluidic chambers to capture and concentrate DNA and RNA. One design consists of a square array of 1,600 pillars, each 10 micrometers in diameter and 10 micrometers from its neighbors; as biological samples flow through this forest of silicon, DNA (or RNA) sticks to the pillars. The captured nucleic acid can later be released by an appropriate buffer; once separated, DNA travels through an exit port to downstream modules for analysis.

Cepheid expects to market a handheld instrument that can accept virtually any biological sample, extract its DNA, and then amplify and detect nucleic acids previously identified to be of interest. Cancer screening, as well as detection of pathogens and biological warfare agents, is among the applications. Full commercialization is expected in several years.