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MEETING NEWS Michael Felton reports from the 16th International Analysis (HPCE 2003)—San Diego, Calif.
Portable CE Portable analytical instruments could provide researchers with timely data in the field without having to preserve samples for the journey back to the lab. Sam F. Y. Li and colleagues at the National University of Singapore have developed a portable CE instrument and have produced a prototype that is about the size of a briefcase and weighs only 3.5 kg with the included power supply. “The instrument was shared between
Prototype of a portable CE instrument.
researchers and students in two labs and was carried around like a notebook computer,” says Li. The primary challenge building a portable CE unit was constructing an integrated detection system, because the typical detection methods, such as UV, are difficult to miniaturize, he adds. Instead, Li chose a potential gradient detector, which generates an electropherogram on the basis of the voltage change along a small segment at the end of the capillary. When a more conductive ion passes through the detection zone, a positive signal is recorded, and the reverse occurs when a negative ion goes through. The device was demonstrated by determining chlorophenoxy acid herbicides in the lab, yielding detection limits for 144 A
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various species from 0.62 to 1.2 µg/mL. However, much better detection limits, between 0.021 and 0.035 ng/mL, were achieved using solid-phase extraction to collect herbicides from water samples and using field-amplified sample stacking, which is a CE preconcentration technique. Li says that the detection limits are good enough for environmental applications.
panded, stretching the PDMS cover, which blocked the sample fluid channel. When the hydrogel was heated, it contracted, opening the channel. “The response times became quicker with the addition of linear polymers to form semi-interpenetrating hydrogel networks,” says Harmon. “It can be anywhere from 10 minutes to 10 seconds.” The more linear polymers that are present, the faster the response.
Isolated hydrogel valves Making valves in microfluidic devices has proven difficult because of the unique interactions of forces at the nanoscale level. One possible solution is to make valves from responsive hydrogel materials. Marianne Harmon at Stanford University presented a new strategy for creating valves in which the hydrogel valve remains isolated from the fluid. The sample fluid therefore had little effect on the hydrogel, and the analyte was not absorbed into the gel. Responsive hydrogels are crosslinked polymers that change size by absorbing fluid when exposed to a variation in the environment, such as changes in temperature, pH, or salt content. Previous hydrogel valves depended on changes in the sample fluid to open and close the valve. This approach requires that the sample fluid contain the activating condition, for example, the proper pH, to open the valve. Sample fluid or analyte can also be absorbed into the hydrogel when it expands to shut off flow, which can lead to trapped material when the hydrogel shrinks. Harmon and colleagues separated the hydrogel from the sample solution by a thin (15- to 40-µm) layer of poly(dimethylsiloxane) (PDMS). To activate the valves, the researchers incorporated resistive heaters and a heat sink. As the hydrogel was cooled by the heat sink, from 46° to 26° C, it absorbed water from a reservoir channel and ex-
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Brain chemistry with CE Although much is known about the chemistry of primary neurotransmitters in the brain, their breakdown products are not well understood. Jonathan Sweedler and colleagues at the University of Illinois–Urbana provide some new insights with their discovery of three new catabolites of serotonin and demonstrate the usefulness of CE combined with wavelength-resolved native fluorescence detection, a variation of CE-laser induced fluorescence. “This system allows us to inject a chemically complex sample such as a [single] cell, look for those compounds that have fluorescence properties like serotonin, but also have electrophoretic properties that indicate it is a different molecule, and then try to characterize only those molecules,” says Sweedler. Detection limits vary on the basis of the fluorescence of the compound being observed; for serotonin, they are typically in the low-attomole range. Other researchers have used components of this approach, like fluorescent detection, but according to Sweedler, his group is the only one obtaining spectra from the fluorescent molecules. Sweedler’s group exposed neurons of the sea slug (Aplysia californica) to serotonin. Using their CE system, they found the previously unknown catabolites, which were identified by MS. Neurons incubated in high heat to denature enzymes and then exposed to serotonin
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failed to produce the three newly discovered catabolites, which indicates that enzymes drive these reactions. Sweedler’s original aim was to confirm what neurotransmitters were released from neurons in different parts
of the sea slug’s brain and to examine the differences between hungry and satiated animals. “We were trying to adapt the system to observe serotonin release and measure the transmitter levels near the release areas when we no-
ticed the unknown compounds,” says Sweedler. They did determine that neurons from different areas of the sea slug’s brain produced significantly different relative amounts of serotonin breakdown products.
GOVERNMENT AND SOCIETY Proteomic standards under way Several efforts are under way to create bioinformatics data standards for proteomics research. In January, the Human Proteome Organization’s (HUPO) Proteomic Standards Initiative (PSI) working group and the American Society for Testing and Materials (ASTM) agreed to collaborate on a generic format for MS data. Members of HUPO’s PSI and other organizations are also developing data standards for protein–protein interaction (PPI) databases, protein arrays, and other proteome technologies. “[The MS format is] something of value for more than just the proteomics community, but [it] has been very difficult [to create] without a user community to help specify what is really needed,” says Randall Julian, chair of ASTM E01.25, which has been developing MS standards as part of the Analytical Data Interchange (ANDI) effort. “Many of the analytical methods used are multidimensional, and their data cannot be represented using the current ANDI standards.” HUPO (www.hupo.org) is an international scientific organization formed in October 2001, which advocates a global proteomics effort. In addition to
bioinformatics, HUPO is coordinating proteome projects on the human liver and plasma, comparing and developing new technologies, and developing projects and array platforms that use multiplexed antibody assays, says Emmanuel Petricoin of the U.S. Food and Drug
Administration (FDA)–National Cancer Institute Clinical Proteomics Program. PSI was born as part of the bioinformatics workshop at a HUPO meeting this past April. In addition to the ASTM collaboration, the MS workgroup has begun modeling a MS data repository for protein sequence information, which could be a central repository hosted either at
the European Bioinformatics Institute (EBI) or some other institute, says Weimin Zhu, of EBI and chair of the PSI MS group. The details, however, will need to be worked out. The MS group also hopes “to collaborate with [the Microarray Gene Expression Data Group (MGED)] in developing common guidelines for experiment description,” adds Zhu. The MGED is an international organization that is focused on establishing microarray data standards and is also interested in proteomics array information. “Several lessons learned during the creation of DNA microarray [bioinformatic] standards, such as object modeling, ontology, and organizing involvement of a wide range of interested academic and industry parties, can be used as a model for developing PSI standards,” says Ugis Sarkans, a member of both MGED and PSI. Zhu hopes to have a MS draft standard by the end of this year. Meanwhile, Henning Hermjakob, with EBI and chair of the PPI PSI group, reports that his workgroup wants to make PPI data compatible with the Biopathways Exchange (BioPAX) format. This would mean that the data would mesh with existing biological pathway databases, such as metabolic, signaling, and genetic regulatory, says Joanne Luciano of the Harvard Medical
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School. “The initial PPI work is helping catalyze future work,” adds Luciano. “We expect to publish XML format and accompanying controlled vocabularies by the summer of 2003,” says Hermjakob. Most of the currently available protein array data can use the first level of PSI PPI format, he adds. Several industry, government, and academic PPI data providers, such as UCLA’s Database of Interacting Proteins, the Samuel Lunenfeld Research Institute’s Biomolecular Interaction Network Database (Canada), the Molecular Interaction Database of the University of Rome, and the French proteomics company Hybrigenics have agreed to use the universal format. The PPI workgroup hopes to include other databases, such as the European proteomics company CellZome and the Gene Information
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Networks database at the Institute of Marseilles (France). According to Hermjakob, HUPO PSI plans to extend their initial efforts in MS and PPI data to general proteomics data, such as gel- and LC-based separation technologies, protein arrays, and isotope-coded affinity tags. Meanwhile, the U.K. Department of Trade and Industry’s National Measurement System is currently funding a project at LGC, the country’s largest independent analytical laboratory, to compare protein array technologies, 2-D chips, and 3-D beads to more standard ELISA plate technologies. According to LGC’s Carole Foy, this work is not currently related to any other protein standards initiatives. “Protein arrays have tremendous potential to impact research and clinical
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diagnostics, but today, there is still little consensus on how to best analyze the data,” says Jeet Mahal of Lumicyte. “The HUPO standards may affect our discovery research by giving us a standard way to compare our results with other MS-based proteomics technologies and possibly integrate data from multiple technologies. However, on the diagnostic side of the equation, we believe that the FDA will approach these technologies on a one-by-one basis and allow the sponsoring company to make the case on appropriate standards.” Mahal therefore concludes, “The industry and the FDA have to work together to define what is a significant result, because in the end, earlier, more accurate disease diagnosis is the real measure of success.” —Laura Ruth
