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Emergency response personnel frequently face risks from hazardous chemicals in events such as tanker spills, pipeline ruptures, and industrial fires. Currently, unknown contaminants are typically identified through manual sample collection or short-range analysis. Such techniques, unfortunately, are both dangerous and time-consuming. Ming Wu, Arthur J. Sedlacek, III, and co-workers at Brookhaven National Laboratory are hoping to take some of the risk out of emergency response by applying the same remote sensing technology that is commonly used to study atmospheric gases. The Mobile Raman Lidar Van (MRLV) can investigate spills of many common solvents from distances of up to 500 m, with a ~500-g/m2 detection limit. The MRLV consists of a 266-nm Nd:YAG laser, a 40-cm Cassegrain telescope, and a spectrometer equipped with an intensified CCD detector. A van tows a diesel generator to power the system in the field. To avoid inter-
Catalytic chromatography Although affinity chromatography is widely used to purify biologically active molecules, it can have problems with enzymes. To improve enzyme purifications, Luis A. Jurado and Harry W. Jarrett of the University of Tennessee and James T. Drummond of Indiana University have turned to what they are calling “catalytic chromatography”, in which elution is based on enzyme catalysis. The technique is similar to affinity chromatography in that it involves an enzyme binding to a substrate, which is immobilized on a column support. Initially, the enzyme is present without a required cofactor, and the enzyme and substrate bind. The missing cofactor is then added, which converts the substrate to product and selectively elutes the enzyme from the column.
ference from ambient light during daytime operations, the researchers chose a laser frequency that falls in the solar blind portion of the spectrum—the frequency range filtered out of sunlight by the upper atmosphere. Range information is collected by varying the delay between a Prototype Raman lidar system in action. laser trigger pulse and a fast shutter in front of the detector. Field tests show that the MRLV FCS theory acquires remote Raman signatures, without prior information about tarSometimes experiments get ahead get substances, in 1 min or less. The of theory. Such is the case with group is also developing a smaller verfluorescence correlation specsion of the device that could be cartroscopy (FCS) of single immoried to an emergency site by hand. bilized molecules. Lars Edman The prototype portable device has of the Karolinska Institute (Swea range on the order of meters, but den) tackles the problem by deit is sensitive to lower contaminant riving autocorrelation functions quantities. (Appl. Spectrosc. 2000, that describe FCS with a single 54, 800–806) immobilized molecule in the presence of many freely diffusing molecules. The theory can help optimize measurements of single molecules, such as biomolecules, The researchers demonstrated the even when the background fluotechnique for the purification of Ecoresces as well. RI restriction endonuclease. In a sinFCS provides data on the temgle step, significantly higher yields poral fluorescence dynamics of and purity were obtained than with molecules, which can arise from affinity chromatography. In addition, such effects as Brownian mothey used the catalytic approach to tion, chemical reactions, or singlet–triplet interactions. In this purify multiple DNA polymerase actipaper, the theory connects “clasvities of Escherichia coli. Five well-resolved DNA polymerase activity peaks sic” FCS of freely diffusing molwere observed. ecules with FCS for a single molAlthough catalytic chromatography ecule. The relationship between should offer increased selectivity, it S/N and signal-to-background does have a few disadvantages. Puriis discussed, and Edman demonfied enzymes could be affected by strates that, under certain condithe reaction product, and because the tions, it is possible to make stasubstrate reacts completely with the tistically useful measurements of enzyme, the immobilized substrate single-molecule dynamics dein the column needs to be regenerspite poor signal-to-background ated or replaced after each use. (Anal. ratios. (J. Phys. Chem. A 2000, Biochem. 2000, 282, 39–45) 104, 6165–6170)
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BROOKHAVEN NATIONAL LABORATORY
Long-distance Raman
