mately 500-1000 times more sensitive than ple extracted from sheeptissue,for examprevious tests. ple, the immunocomplex peak is reduced. The amount of prion protein that can be Most of the work characterizing prions detected with this technique is in the femhas been done with scrapie (TSE in sheep) tomole range or —100 pg. The assay takes introduced into mice or hamsters. How~ 2 min. Its sensitivity has allowed testing ever, because the prions found in different species could differ in subtle ways, the pro- of real samples and tissues witii low concentrations of prion protein, including teins are best characterized directly from lymph nodes and blood. infected animals. Before die development of CE techniques, the characterization of Another analysis method for prions inPrP from sheep was difficult because of the volvestime-resolvedfluorescence. The Dislow amounts of the prion protein. sociation Enhanced Lanthanide Fluoroimmunoassay (DELFIA) system, developed At die 2nd International Conference on by Ilkka Hemmila at Wallac (Turku, FinTransmissible Spongiform Encephalopathies, held in Washington, DC, last Novem- land), can be used to run assays of prion ber, Mary Jo Schmerr of the National Animal protein from animal tissue samples. Disease Center in Ames, IA described a The prion analysis application of capillary immunoaffinity electrophoresis DELFIA was developed by Geoff Barnard, metiiod for prions. Five peptides from the a biochemist at the Institute for Animal prion protein are synthesized witii a fluores- Health (Compton, U.K.), and is based on a cein attached through a y-butyric acid link to capture antibody that can bind PrP in the the N-terminus of each peptide. An antibody presence of a small amount of guanidine specific for each peptide is produced in rabhydrochloride, which solubilizes the prion bits and affinity-purified. After an incubation protein from brain homogenate. The signal of the fluorescein-labeled peptide with the antibody, which binds to the captured antibody, the peptide is injected into a 20-um prion protein, is labeled with an Eu(III) i.d. capillary and run at 30 kV. chelate so that die prion will fluoresce and can be analyzed. Frey Lindqvist of EG&G When die antibody is present, two fluo^^allac Inc saystiiatSm(III), Dy(III), and rescence peaks are observed—one for the Tb(III) chelates also could be used as lafree peptide and one for the immunocombels in protein analyses. plexed peptide. If PrP is present in a sam-
Field analysts keep up the pace "Faster, better, and cheaper chemical analyses" are what Albert Robbat, Jr., director of the Center for Field Analytical Studies and Technology at Tufts University, strives for. "The key to being able to go out into the field and provide cost-effective hazardous waste site cleanup is the ability to analyze samples quickly." To better match the rate at which samples can be analyzed with the speed at which they can be collected, you need to be able to analyze a wide range of environmental contaminants all at the same time, he emphasizes. To provide near real-time chemical measurements, Robbat and his colleagues have set out to simultaneously analyze the full range of organics targeted by die Environmental Protection Agency (e.g., polychlorinated biphenyls, pesticides, polycyclic aromatic hydrocarbons, and other contaminants that may be present in environmental samples). They created data-analysis software and built a thermal desorption sample introduction system, which together were
"This method offers a high degree of specificity and sensitivity," Barnard told the Fourth Annual Conference on Blood Safety and Screening, held in McLean, VA in late February. Barnard told Analytical Chemistry that detection to attomole levels is possible. Lindqvist and Barnard explaintiiatthe long emission decaytimesof the lanthanides permit the measurement window to be optimized by allowing the minimization of the background and the maximization of the signal. Typically, counting time starts 400 us after excitation and continues for 400 us; the initial 400-us delay eliminates noise from nonspecific fluorescence. Barnard and Lindqvist add that the large difference in excitation and emission wavelengths (almost 300 nm) further improves the signal-to-noise ratio At the conference Barnard expressed hope that the specificity of the DELFIA system could be applied to detecting minute amounts of PrP80 in samples derived from human and animal tissue and thereby help eliminate die risk of CJDfromthe use of such materials Botii of these new approaches could lead to die control of the disease in die animal populations of the world and could help die pharmaceutical industries ensuretiiatdie materials they produce are free of PrP50. Julian Josephson
able to quantitatively analyze a wide range of organic compounds in oilbased matrices in
