Test equipment suppliers like Cascade Microtech Inc. (Beaverton, Ore.), meanwhile, are retooling their electronics expertise for fluid processing, reasoning that the microfluidic lab-on-chip market will need high-precision metrology (see story, page 22). Cascade Microtech, which claims a 50 percent share in the wafer probe market, believes its new L-Series for testing microfluidic chips will elevate the company to similar status in bioengineering.
Labs-on-chip were the natural extension of a technology borrowed from semiconductor fabrication namely, the microarray. Microarrays, or chips with an ordered set of known molecules on the substrate, are employed in everything from medical diagnostics to law enforcement. Microarray nucleic-acid analysis enables the early detection of genetic diseases, fingers serial killers and helps in the design of new drugs. Down the road, microarrays of tissue proteins proteomics could one day reveal how to generate custom therapies by synthesizing the perfect building blocks to repair diseased organs, cells and tissues.
Detection using microarrays usually begins by amplifying a sample in order to expose the entire microarray to it at the same time and then checking to see which elements of the array emitted a response. This is usually done using fluorescent tags, although some microarrays use radioactive or chemiluminescent tagging and others rely on embedded electrodes, which detect electrical changes within the elements of the array when it reacts to a sample, thereby yielding real-time feedback.
Microarrays for drug discovery and medical diagnostics already harness MEMS for vast parallelism, but microfluidic chips will extend that utility to handheld instrumentation. Microfluidic chips will make it possible for handheld devices to perform ad hoc microarray assays, enabling microfluidic labs-on-chip that might range from one-function disposable field health tests say, to test a soldier for anthrax exposure to complete, reusable testers capable of amplifying samples for microarray analysis, electronically monitoring the results, self-cleaning and performing an entirely different experiment minutes later.
Engineers collaborating with chemists are now creating a vast array of these laboratory-on-chip devices for applications as diverse as homeland security, point-of-care medical diagnosis and environmental monitoring.