"Lab On A Chip" For DNA Testing

The device---a glass-and-silicon chip smaller than a child's pinky finger---is far less expensive than conventional methods of analyzing DNA (which require specialized laboratories, equipment, and personnel) yet just as quick and sensitive.

It is expected that the "lab on a chip" will be the key component in simple, low-cost, portable instruments that replace the current technology and make DNA analysis widely available.

The broad availability of simple DNA testing equipment should produce major benefits in many fields, including medical diagnostics, forensics, and agriculture. Among the potential applications are the diagnosis of infectious diseases in minutes rather than days, rapid identification of crime suspects, and on-the-spot categorization of endangered species in remote locations.

The invention is the product of five years of work by chemical engineering Prof. Mark A. Burns, along with Profs. David Burke (human genetics) and Carlos Mastrangelo (electrical engineering and computer science) and their colleagues. The work was funded by grants from the National Institutes of Health totaling nearly $3 million.

Their method of micro-fabricating a fluid and electronic chip capable of complex chemical analysis is detailed in the Oct. 16 issue of the journal Science, in an article by Burns titled "An Integrated Nanoliter DNA Analysis Device."

The chip includes systems for metering, measuring, and mixing microscopic liquid samples of DNA with reagents, moving the mixtures to an integrated, temperature-controlled reaction chamber, separating DNA molecules by size (through gel electrophoresis), and determining the results with an on-board fluorescence detector.

All components are contained on a single glass-and-silicon wafer, except for external light and air-pressure sources and a printed board containing control circuitry. One key to micro-fabricating the chip was the team's development of a photo-lithographic technique for etching precise hydrophobic regions in the injection channels of the silicon layer.

In contrast to DNA analysis in a standard laboratory---which relies on human intervention at several stages to manipulate or observe samples and record results---the self-contained "lab on a chip" represents an almost "hands free" technology.

The team's success with the DNA-testing chip suggests that similar integrated systems can be constructed at the nanoliter scale using sample and reagent volumes far smaller than those needed in typical human or robotic handling methods.

Cost savings should be a major byproduct because of increased processing speed; lower expenses for labor, equipment, and material; as well as inexpensive production through photolithography.

Preliminary estimates by Burns suggest that the cost of producing the DNA-testing chip in research-sized quantities may be approximately $6 per device. Mass production would lower that amount considerably.