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Droplet-based microfluidics reveals dynamics of pancreatic islet secretion says. His team set out to build a simple cate the setup. The FluoZin-3 was imaged David Piston and his colleagues at quantitative microfluidic device with high using a confocal fluorescence microscope, Vanderbilt University Medical Center temporal resolution. though the researchers say a simpler optical have combined a microfluidic chip that scheme could have been used. uses droplet technology with The researchers fine-tuned fluorescence detection to many aspects of the device to achieve temporal resolution fast achieve the desired results. “A big enough to quantitatively meaissue was the quantitation of nasure zinc secretion from indinomolar zinc pulses in the presvidual pancreatic islets. This ence of trace impurities and milliinformation could be useful for molar levels of calcium and understanding what goes magnesium in the cell imaging wrong in the islets and leads to buffer, which was achieved using diabetes. The work is described the slow ligand transfer kinetics of in a new AC paper (2009, a saturated metal chelator,” Piston DOI 10.1021/ac9017692). says. A pancreatic islet is a group Landers comments, “The of cells that secrete insulin, and packaging of the secreted analytes when they stop working, diabeinto droplets, combined with tes can develop. “We have having control over the sampling wanted to measure single islet rateOusing the speed of droplet insulin secretion for a long The channel layout of the microchip is shown along with images of an formationOprovides a temporal time,” Piston says. “Most exislet (top left; scale bar ) 100 µm) and droplet formation (lower right; resolution that yields unprecperiments have been done on scale bar ) 500 µm). edented information about the large populations because difbiology of these cells.” fusion of the insulin into media Insulin secretion can be assayed by The researchers used the device’s tempomakes the concentration very low.” Unmeasuring the zinc ions co-secreted with ral resolution to identify two classes of oscilderstanding the process of insulin secreinsulin in the -cells of the islets. The milations in secreted zinc. They detected fast tion on the molecular level could reveal crofluidic device the researchers fabricated periods at ⬃20⫺40 seconds and slow ones more about how and why diabetes had PDMS channels and a glass coverslip at ⬃5⫺10 minutes, with the former matchdevelops. floor, and it measured zinc ions with the ing closely with intra-islet calcium oscilla“For normal insulin secretion, calcium FluoZin-3 fluorescence indicator. A single tions and the latter with insulin pulses typientry drives exocytosis, but in vivo activation islet was loaded onto the chip, which was cally measured from bulk islets. These of G-protein-coupled receptors can moduheld on a microscope stage. The secreted findings weren’t unexpected, but if the mealate secretion in the presence of normal calmolecules were stored in aqueous-in-oil surements can be definitively correlated, cium signals,” Piston says. “There are also droplets that were created on chip. The then Piston says they can explore more interpathologies where secretion is impaired, and ⬃0.47-nL droplets preserved the temporal esting questions about biological function, some of those are thought to be caused chemical information, allowing reconsuch as the specific molecular mechanisms at downstream of calcium signals. Until now, struction of the secretion timing from a play in a zinc transporter defect linked to there has not been a simple way to assay single islet. diabetes risk. changes in this part of the pathway directly.” James Landers from the University of Mike Roper of Florida State University Because all the cells in the islet secrete Virginia says that unlike some macroscale says, “The use of a single syringe to drive all insulin in synchrony, Piston points out that methods, the Vanderbilt method doesn’t the flows in the device and to create the waexamining secretion from single islets allows dilute the zinc. This allows sensitive detecter droplets is a good example of how a the study of physiological modulations or tion, a high sampling rate, and unpreccomplete microfluidic system can be driven pathological defects in secretion that might edented temporal resolution. with very simple controlsOwhich will be occur downstream of calcium entry. The channel flow is controlled passively needed to move microfluidic devices from Other research groups have built devices by a constant vacuum applied to the chip’s researchers’ labs into the hands of nonspefor measuring islet secretion, but those deoutlet by a single handheld syringe, eliminat- cialists.” vices were complex, had limited temporal —Nancy D. Lamontagne ing the need for syringe pumps or electrical resolution, or were unable to quantitatively components on the chip, which can complimeasure insulin secretion dynamics, Piston 10.1021/AC902380M 2009 AMERICAN CHEMICAL SOCIETY
Published on Web 10/27/2009
DECEMBER 1, 2009 / ANALYTICAL CHEMISTRY
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