News sor. Onefluorophoreis sensitive to the analyte, and it has a nanosecond decay time. A second fluorophore, which does not respond to the analyte and does display a longer decay lifetime, is included. The mixture of the two lifetime fluorophore determines the modulation of the fluorescence emission at low frequencies—1-10 MHz, which are even lower than radio frequencies. "The intensity of the sensing fluorophore with a short decay time is revealed by the modulated signal at low frequency," explains Lakowicz. The researchers determine the modulation, which is equal to the fractional fluorescence intensity of the sensing molecule. The analyte concentration can be calculated from the fractional fluorescence intensity The sensor's modulation response is independent of the total fluorescence signal. The only requirement is a fluorophore that changes intensity in response to changes in the analyte concentration. However, fluctuations in the total signal don't affect the results, because the most important factor is the relative amplitude of the sample and reference fluorophores, which are immediately adjacent in the sensor.
The team has tested the idea using two mixtures: a system containing 6-carboxyfluorescein acting as a pH sensor and the organometallic fluorophore [ruthenium 2,2'(bipyridyl)3]2+ as the modulator. A calcium probe was made by replacing the fluorescein with Ca2+-sensitive Fluo-3. The most important advantage of modulated sensing, however, may be the range of analytes that can be measured. Numerous sensingfluorophoresthat change intensity in response to analytes are known. The extension to immunoassays is also possible, adds Lakowicz. Aside from the fact that modulated sensing with such a system can be used with less than ideal samples, including living tissue, it is also unaffected by disturbances to the equipment itself such as fiber optics being bent or the sample being moved. "The availability of numerous fluorophores, which are sensitive to a wide variety of analytes, makes this approach widely applicable," adds Lakowicz. Commercialization of modulated sensors for industrial and clinical applications is likely in the near future, he says. David Bradley
Rapid angle on wood stiffness
ter and charge-coupled device (CCD) detector have opened new possibilities in wood fiber diffraction. With the help of physicist Ian Cave, the team has developed protocols for rapid measurement of a key parameter related to timber quality. The powerful data-acquisition and handling capabilities of the detector allow the angle of crystalline microfibrils in wood cell walls to be determined at a rate of one sample every few minutes. Robinson emphasizes that the same measurement can be made withfilmdetectors, although it requires several hours per wood sample. Traditional X-ray diffraction methodology is unsuited to large numbers of samples. The advantage of the area detector is its speed, making possible for thefirsttime the mass screening of microfibril angles (mfa) in plantation seedlings and trees. The wood of softwood species is made up predominantly of tracheids, which are the skeletons of dead cells. Highly ordered bundles of cellulose chains (microfibrils) are embedded in the amorphous matrix of the tracheid cell wall, giving strength and stiffness to the cell wall. The microfibrils form a right-handed spiral that makes an angle (mfa) with the cell axis. Wood cell
Modern array detectors have revolutionized single-crystal structure analysis, and they are now indispensable for protein crystallography. At the Asian Crystallographic Association Conference in Bangi, Malaysia, crystallographer Ward Robinson and co-workers from the University of Canterbury (New Zealand) described how their X-ray diffractome-
Orientation of the microfibrils in the S2 layer. 20 A
Analytical Chemistry News & Features, January 1, 1999
walls consist of several layers of different compositions, and the mfa of the tracheid S2 layer (the middle layer of the secondary cell wall) has the greatest impact on the mechanical properties of wood. Low values of mfa tend to give the best mechanical properties (10-20° is considered optimum) . The mechanical properties of wood determine its use and economic value— hence the interest in mfa measurements. In Robinson's laboratory it takes about one minute to mount each microtomed wood sample on the goniometer and to record the wide-angle X-ray diffraction pattern. Sample thicknesses up to approximately 16 mm can be probed, although the overall sample dimensions are not critical. The data analysis provides a frequency distribution of mfa in the 1-mm diameter cylin der of material sampled by the X-rays. Robinson points out that a considerable amount of work lies behind the data-analysis procedure. Compared with single-crystal diffraction patterns the wood patterns are "dirty" with contaminant reflections and they require sophisticated mathematical methods for analysis The methods were developed by co-worker Cave and are applied using commercial mathematical software packages Robinson became interested in applying modern X-ray diffraction instrumentation t< mfa measurements when he was approached by a multidisciplinary research team of foresters, engineers, and plant scientists. The team is studying aspects of mf; in Pinus radiata, which accounts for more than 90% of plantation forest area in New Zealand. This pine grows rapidly; however, its wood has poor mechanical properties, compared with wood from other softwood species. Modest gains in wood stiffness can yield significant economic benefits; this advantage suggests focusing breeding and silviculture methods on reducing mfa. The possibility of rapid and low-cost measurement of mfa in many samples is exciting foi the research team One study by the team has demonstrated that seedling clones that have the potential to produce stiffer wood can be identified by measuring the mfa of their first annular growth rings. Of more immediate importance, mfa surveys can also be used to increase the economic yield of existing forest stands. Wood stiffness can vary widely within a plantation, and measuring the mfa of individual trees during harvest could dramatically reduce waste by tailoring the use of the log to die wood stiffness.
Robinson envisions the possibility of participating in large-scale screening programs when interest in the facility spreads in New Zealand and overseas. Plant breeders at New Zealand's Forest Research Institute have recently provided 1400 samples for mfa measurement, and miscellaneous samples are arriving from around the world for preliminary study. A particularly rich and interesting diffraction pattern was collected from jute samples from Bangladesh and has led Robinson to think about the wider possibilities of fiber diffraction. He explains that initial surveys of materials such as cotton and wool were undertaken in the 1940s and 1950s however the diffraction patterns were difficult to interpret and little use has been made of the diffraction data Robinson believes that many potential applications of fiber diffraction exist and with the availability of modern area detectors and data handling techniques it may be time to re-investigate these materials Alison Downard
BUSINESS Dionex acquires Softron In October, Dionex (Sunnyvale, CA) announced that it had purchased Softron, a privately held German company specializing in HPLC systems. Softron's products are marketed predominantly in Europe and have generated annual revenues of $10 million in fiscal year 1997. Dionex reports that it expects an after-tax charge against earnings this year of between $6 and $8 million for the Softron acquisition.
Analect becomes part of Orbital Orbital Sciences (Dulles, VA) acquired Analect, a manufacturer of FT-IR and I'T-near IK analyzers for the process analytical market, in October. Orbital plans to merge the company into its Applied Instrument Technologies business based in Ponoma, CA. Orbital's business currently focuses on space, satellite, and Earth-imaging services. According to Orbital's management, the purchase of Analect will help the company gain entiy into the chemical and polymer markets.
PEOPLE
Therese M. Cotton 1939-1998 Therese M. Cotton passed away on October 26,1998, after a four-year battle with ovarian cancer. Therese received her A.B. from Bradley University in 1961. After starting a family and working for a few years as a research assistant at the USDA's Northern Research Laboratory in Illinois and at the Argonne National Laboratory, Therese began her graduate studies with Paul Loach at Northwestern University and Joseph Katz at Argonne She then began a postdoctoral stint with Rick Van Duyne and was awarded NSF IBM and NIH postdoctoral fellowships She su,bsequently held faculty appointments at the Illinois Institute of Technology the University of Nebraska-Lincoln and Iowa State University She served as a'member of the Analytical Chemistrv A-Page Advisory Panel from 1W to 1995 Her scientific achievements reside primarily in the development and application of resonance and surface-enhanced Raman spectroscopies as tools for the characterization of biological systems. She was the first to recognize and exploit the capabilities of this technique, and her numerous innovations are testimonies to her genius in experimental design. In particular, Therese's contributions to the electrochemistry, photochemistry, and photoelectrochemistry of biological molecules placed her as stated by Van Duyne, "without peer in this area of science". She publishep more than 150 papers and continued to work energetically during her couragtous struggle against this debilitating disease. In recognition of her research accomplishments, Therese rereivea numerous awards, including the Lester Strock Award, which is given by the Society of Applied Spectriscopy for seminal publication (s) ovec afive-yearperiod preceding the award. She was particularly proud of the Distinguished Alumnus Award she received recently from Bradley University. Therese is survived bl three children,
six grandchildren, and more than 60 past and present members of what is known around the Iowa State University campus as the "Cotton Club". Even while ill, Therese served as a role model for the members of her research group as well as her family and many friends. Richard Walsh, a graduate student in Cotton's group, said, "Dr. Cotton is going to live on in my mind, forever teaching me how to be a better person. This is the mark of a powerful teacher." Therese was a role model for us all. She was a unique mix of parent, scientist, teacher, mentor, colleague, and friend. Her courage, spirit, and intellect will be missed by all of us. Marc D. Porter and Edward S. Yeung
New Advisory Board and A-Page Advisory Panel members appointed Advisory Board
Six new members from government, academia, and industry have been selected to serve three-year terms on Analytical Chemistry's Ediiorial Adviiory Board. Each January, membership is rotated as new appointees replace members whose terms have expired. The chair of the ACS Division of Analytical Chemistry serves a one-year term as ex officio representative of the Division. Established in the 1940s to advise the Journal's editors, the board meets formally once a year at ACS headquarters. The board members are a vital link between the editors and the analytical chemistry community, providing guidance and advice on editorial content and policy. Luc Bousse, research director at Caliper Technologies, received an electrical engineering degree from Vrije Universiteit Brussel (Belgium) and his Ph.D. from Twente University (The Netherlands) . His research interests include systems-level analysis in microfluidic devices, microfluidics, microfabrication, electrokinetic transport, and chemical and biological sensors.
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