NEWS FROM MICRO-TAS Elizabeth Zubritsky reports from Banff, Alberta (Canada).
PCR or DNA digestion, and separates and detects products. No external lenses, heaters, or mechanical pumps are needed. All of the interconnections are standardized, and everything is microfabricated on a single glass and silicon substrate, except the excitation source, the pressure source, and the control circuitry. The device is able to meter small, accurate volumes (1-120 nL demonstrated) from a sample using injected air to move the fluid and hydrophobic patches to stop it. Reactions are performed on board in a temperature-controlled chamber, and separations are performed on electrophoretic gels that "look exactly like macrogels, ex-
controlled by regulating of the potential of the sample and reagent channels. If the potential of one channel was held constant Micro-TAS 1998 and the other changed, the reactants could Amid the mighty peaks of the Canadian be mixed in various ratios, permitting onRockies, researchers showed that the minboard calibration. iature world of micro-TAS (total analysis Tests of the self-calibration function systems) is climbing to new heights. At the using fluorescein-labeled bovine serum meeting in Banff, speakers presented sysalbumin (BSA) and an antibody against tems for tasks from sequencing to cell sortBSA yielded estimates of concentration ing and components for steps from mixing that were 98±6% of the known values, indito mass spectrometry. The talks revealed cating that the voltage-controlled mixing progress in many areas, including microwas accurate. More importantly, Attiya fabrication, for which new techniques were said, the results showed "that you can do a developed for photopolymers, Teflon, and whole immunoassay on a chip." plastics—including plastic films that come Still, integrated systems are not limin rolls. The integration of optics ited to liquids. One of the is also expanding, encompassing gas-phase systems was prestrategies such as stacked arrays sented by Greg Frye-Mason of microlenses and detectors and and colleagues at Sandia Nathe use of evanescent waves to tional Laboratories, who are selectively excite fluorophores developing it as part of an Work continues on techniques integrated laboratory for the for DNA extraction fluid mixing detection of chemical warand metering and product sepafare agents. The system uses rations Despite the focus on apa "cascade" approach: A plications several researchers small adsorbent sample colpresented talks on the theory lector/concentrator leads to a GC column that feeds a id roverine- the optimization surface acoustic (SAW) of on chip CE or the development of numerical methods to analvze detector fluid flo in c o m d e x micros A thermally isolated tems, for example. heater allows rapid desorption of the analyte from the Perhaps the best indication of Banff, Alberta, Canada: the setting for this year's Micro-TAS workshop. collection membrane. The the field's maturation, though, is separation is then performed the number of systems that intein a meter-long spiral channel that has grate a significant amount of sample prepa- cept they're tiny," Burns said in his talk. been cut in a cm2 area using deep ion ration, analysis, and detection on a single Separation can be achieved in 0.5-3 mm, etching. These "columns" have perdevice. "Two years ago, the promise [of an and the products are detected with microformed separations in about 30 seconds integrated device] was there. Now the fabricated fluorescence detectors. The depromise has been fulfilled," said Jed Harritection system, which uses an external blue with minimal pressure (4 psi). "We don't son this year's meeting chairman. He LED and an integrated photodiode and fil- get 100,000 theoretical plates as in the liquid phase," Frye-Mason said in his talk. noted that saying a device is integrated ter, has registered DNA concentrations as "But for our needs, the separation is does not necessarily mean that it is a stand- low as 10 ng/uL. alone microchip unit that's not appropriAnother device, made by Jed Harrison's good." group at the University of Alberta and decite in every case. What researchers have The last component, the SAW detector, shown he says is that they can miniaturize scribed by Said Attiya, was designed for is well-suited to micro-TAS because its immunoassays. Replacing a basic sample and integrate critical parts and get good mass sensitivity improves as the device inlet was a large port (300 um deep x 1 mm gets smaller, Frye-Mason said. Although performance A sampling of these intewide x 2 cm long) that could accommodate temperature sensitivity has always been an grated systems followed by two other seflow rates up to 5 cm/s without disrupting lections from the meeting are provided issue with SAW detectors, he notes that the other channels on the chip. This arbelow this application only requires stability over rangement permitted rapid sample exa matter of seconds. Nonetheless, future One system for DNA analysis was prechange and real-time monitoring. Downdevices probably will include temperaturesented by Mark Burns from the University control circuits, as well as modifications to of Michigan. He and his colleagues created stream were channels for mixing, for reaction of antigen and antibody, and for adapt the detectors to the low flow of the a 5 x 47 mm device that measures and separation of the product. The mixing was GC columns. mixes solutions, runs reactions such as Analytical Chemistry News & Features, December 1, 1998 775 A
