Just Released! MATERIALS CHEMISTRY iBrgB^ Oiscîiîbae iscîiîbae iscîiîbae iscîiîbae iscîiîbae
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Materials Chemistry: A n Emerging Discipline
M
aterials science has been known as a discipline only for the past 40 years, yet its importance cannot be overstated. Now, this 21-chapter book provides an overview of the field and includes discussions of government, academic, industrial, and educational issues as well as reports of current research. Covering a range of materials types as well as various approaches to their preparation and study, Materials Chemistry examines key frontier areas of research, ranging from oxide superconductors to polymers and biomaterials and from chemical vapor deposition to scanning tunnelling microscopy.
Contributions from many of the leading scientists, engineers, eductors, and policy planners in the field, including D. Pravden Chaudhari, Dr. Mary Good, and Dr. Mark Wrighton, are present. Leonard V. Interrante, Rensslaer Polytechnic Institute, Editor Lawrence A. Casper, University of Wisconsin—Madison, Editor Arthur B. Ellis, University of Wisconsin—Madison, Editor Advances in Chemistry Series No. 245 400 pages (1995) Clothbound ISBN 0-8412-2809-4 $79.95 ORDER FROM American Chemical Society Distribution Office Dept. 74 1155 Sixteenth Street. N W Washington. DC 2 0 0 3 6 Or CALL TOLL FREE 1-800-227 5 5 5 8 (in Washington. DC 872-4363) and use your credit card! FAX: 202-872-6067. ACS Publications Catalog n o w available on internet: gopher acsinfo.acs.org
ACS PUBLICATIONS Essential Resources for the Chemical Sciences
Focus several water utilities in the United Kingdom with reported overall recoveries of ~ 30% for Cryptosporidium (10). Microbiologists worry that many of the oocysts detected in the above methods are not viable and that the numbers are therefore misleading. One method in development that does determine viability is based on a technique called FISH (fluorescent in situ hybridization), which labels a section of ribosomal RNA with a complementary RNA fluorescent probe. Ribosomal RNA degrades quickly in nonviable cysts or oocysts, leaving FISH RNA probes to mark primarily viable cells. FISH can be combined with confocal microscopy to look at samples simultaneously marked with multiple fluorochromes. For example, says Schaefer, it is possible to fluorescently label the surface of Giardia cysts and the ribosomal RNA. Identification and confirmation are thus combined in one step. Alteratively, FISH can be used with flow cytometry to select viable protozoa. Microscopy combined with imaging by a cooled, slow-scan charged coupled device provides another way to look at pathogens tagged with multiple fluorescing probes. This technique works with lower magnification microscopy, but the big limitation so far is the software, says Schaefer. In vitro cell culture is another route for detecting viable infectious forms of Cryptosporidium. Following a purification process such as that used in IFA, the sample would be exposed to chlorine to kill off everything but the tough oocysts and then prompted to begin its parasitic life cycle by introduction into a tissue cell line. Initial work indicates the method requires as few as 100 oocysts for a response. Other methods to test viability rely on the simultaneous exclusion and inclusion of certain dyes, or an enzyme test. Some scientists express high hopes for a method called electrorotation assay in which oocysts bind to the antibody-coated particles, which are then spun in a rotating ac electric field. Bound and free particles spin at different rates. The method reportedly also differentiates between viable and nonviable oocysts. Most research microbiologists are skeptical of these claims, however, pointing out that the procedure has not been published in the peer-reviewed literature or exhaustively
734 A Analytical Chemistry, December 1, 1995
tested. "It's an entirely new method and each step will need to be checked," says Schaefer. Nevertheless, Hach Chemical (Loveland, CO) plans to offer a reagent kit for the method early next year, according to company microbiologist Jill Plyter. "We feel very confident about the method," says Plyter. And, she confirms, it will discriminate among viable and nonviable pathogens. None of these analytical methods replaces turbidity as a real-time measure for pathogens. At best, the direct detection methods require 24 hours—too long for water utilities, which must keep treated water flowing. However, turbidity measurements do not protect against protozoa in lowturbidity waters. Although still an indirect indicator of pathogens, particle counting is currently under investigation as a better means of real-time analysis because the technique determines particle sizes and thus warns of particles in the size range of oocysts and cysts. Rose warns that other analytical issues need to be resolved, such as where to sample, how sensitive a method must be to provide meaningful data, and how often to sample. "I can measure log reductions [in Cryptosporidium concentration]," she says. "But are they real reductions?" Alan Newman References (1) Clancy, J. L.; Gollnitz, W. D.; Tabib, Z. J.Am. Water Works Assn. 1994,86(5), 89-97. (2) LeChevallier, M. W. et al. Appl. Environ. Microbiol. 1995, 61, 690-97. (3) Nieminski, E. C; Schaefer, F. W.; Ongerth, J. E. Appl. Environ. Microbiol. 1995,62,1714-19. (4) Fed. Regist. 1994, 59, 6332. (5) Fed. Regist. 1994, 59, 38832. (6) Fed. Regist. 1994,59, 38868. (7) Haas, C. N.; Rose, J. B.J. Am. Water Works Assn. 1995,87(9), 81-84. (8) Rodgers, M. R.; Bernardino, C. M.; Jakublowski, W. Water Sci. Technol. 1993,27,85-88. (9) Bifulco, J. M.; Schaefer, F. W. Appl. Environ. Microbiol. 1993,59, 772-76. (10) Watkins, J.; Kemp, P.; Shepard, K. In Protozoan Parasites and Water; Betts, W. B. et al., Eds.; Royal Society of Chemistry: Oxford, U.K., 1995; pp. 115-21. Suggested reading Protozoan Parasites and Water; Betts, W. B. et al., Eds.; Royal Society of Chemistry: Oxford, U.K., 1995.
