An enzyme solution eats away the proteins in the cells, leaving the DNA and RNA intact. The resulting melange of molecules is then pumped out, and the genetic material is analyzed by another chip. The 25-electrode chip can also be used to separate cervical cancer cells from blood cells, Cheng and his colleagues report in the June 1 Analytical Chemistry. C hip makers have found that miniaturizing chemical processes results in a set of problems different from those routinely encountered in a conventional laboratory. Molecules or biological cells inside a chip so frequently encounter the material that contains them that they may undergo unwanted chemical reactions.
Many companies prefer to make microchips out of glass, which interacts the least with samples.
Plastic is cheap, which makes it a good choice for disposable chips, says Knapp, but it has more surface reactions and may not be as durable as other materials. Silicon dissipates heat better than glass, getting rid of temperature variations that can push cells where they are not supposed to go. To mask the reactivity of the silicon surface, researchers have developed various ways to put down barrier layers. At Nanogen, scientists deposit a gel on the walls that makes the silicon nonstick. A scientist could simply plug in a cartridge containing the chip appropriate for a test.