the DNA. What they discovered is that all three are quite similar, with sequence homology on the order of 99%. This suggests that all three samples contained a single strain of HIV-1. The three samples of BRU HIV-1 DNA, however, are quite different from LAV DNA and HTLV-IIIB DNA, with sequence homologies between BRU and LAV and between BRU and HTLV-IIIB on the order of only 90%. In other words, BRU clearly was infected with HIV-1, but he almost certainly wasn't infected with either the HTLV-IIIB or LAV strains of the virus. No one now knows the origin of either HTLV-IIIB or LAV. It is possible that Montagnier's BRU isolates became contaminated with HTLVIIIB samples provided by LTCB. It is also possible that the two laboratories received material from the same patient, and virus from that isolate contaminated the BRU isolate. Gallo and his NCI collaborators have been operating under the scrutiny of the National Institutes of Health's Office of Scientific Integrity, so, unless they are interested in committing collective professional suicide, it is hard to imagine that the present work is anything other than completely aboveboard. The presence of Chermann as a signatory to the present report presumably attests to the authenticity of the 1983 samples that have been reanalyzed. Clearly, a scientific mystery exists: What is the origin of HTLV-IIIB/ LAV? According to an NCI spokesman, Gallo's group is currently attempting to analyze DNA from all 10 isolates that Popovic pooled to first isolate HTLV-IIIB. Montagnier has told the New York Times that he plans to reexamine material from BRU to clear up the mystery of the origin of HTLV-IIIB/LAV, while rejecting the possibility that material in his lab could have been contaminated by virus sent from LTCB or some other source. Why? It is well known that cross contamination of samples is the bane of retrovirology* It happens all the time. It has already happened to other prominent AIDS researchers. And many observers inside and outside the AIDS research community (including Montagnier) have been
not yet discovered a likely candidate. Others still subscribed to other possibilities. In the spirit of cooperation that infused AIDS research in those early days, before visions of Nobel Prizes and patents on AIDS blood tests undermined collegiality, material was being sent from clinicians trying to treat AIDS patients to laboratories around the world. It's not surprising that the origin of the first sample of HIV-1 is a mystery. The point is, it doesn't matter. Two of the finest biomedical research organizations in the world have been wrangling over the origin of HIV-1 for almost six years. A cloud has been cast over the reputation of one of the most brilliant and productive AIDS researchers in the world. Meanwhile, more than 100,000 Americans have Gallo: viruses are distinct died of AIDS; well over a million more than willing to suggest that others are infected with HIV-1. The contamination of viral isolates at disease has cut a terrible swath of LTCB might be the cause of the sim- suffering and death across Africa and ilarity between HTLV-IIIB and LAV. threatens to do the same in Southeast It is not at all clear why the explana- Asia. The dispute over the origin of tion might not apply to isolates at HIV-1, a scientific and medical sideshow that has been a useless distracthe Pasteur Institute. People forget that in 1983 AIDS tion from the important work of batwas a terrifying new disease, and tling the AIDS epidemic, should now that no one knew its cause. Gallo, be turned over to the historians of Montagnier, and others strongly science. suspected a retrovirus, but they had Rudy Bourn
Electronic nose moves closer to reality Progress is being made toward development of an "electronic nose." A project moving in this direction was described in Chicago early this month at the Pittsburgh Conference & Exposition on Analytical Chemistry & Applied Spectroscopy by chemistry lecturer Philip N. Bartlett of the University of Warwick, Coventry, England. The rationale behind the project is the reliance that people have on their sense of smell to judge the quality of such products as beverages, foods, perfumes, and cosmetics. Thus, an artificial olfactory system might lend a new dimension to analyses of chemicals and mixtures of chemicals. It might also lead to improved understanding of the human sense of smell. In humans, odorant molecules interact with 50 million olfactory sensory cells in surface tissue called the
olfactory epithelium. Electrochemical signals from each receptor are transmitted through one of 50 million neurons, which in turn are collected into an average 10,000 bundles called glomeruli. Each glomerulus interfaces with one of 10,000 mitral cells, so called because they resemble a bishop's miter in shape. Sensory neurons are only weakly selective to odorants, while mitral cells respond selectively to such distinct odorant categories as "fruity" and "pungent." It is these preliminarily reduced data that are sent to the brain's olfactory lobe. Working with chemistry lecturer George H. Dodd, and engineering lecturers Julian W. Gardner and Harold V. Shurmer, Bartlett used an array of 12 tin oxide gas sensors to mimic the biological sensory cells. These connect to 12 analog-todigital converters (ADCs), which March 25, 1991 C&EN
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Science/Technology serve the function of neurons in generating and transmitting electrochemical impulses. The ADCs connect to a microcomputer, whose artificial neural network programing simulates the data processing of one mitral cell. The video display of the microcomputer corresponds to cognition in the olfactory lobe. In actual practice, the microcomputer program simulated five mitral cells, which were imagined to interact reciprocally with one another to analyze data from and distinguish among five vapors and to characterize mixtures of these. The vapors were methanol, ethanol, isopropanol, 1-butanol, and 2-methyl-l-butanol. The Coventry researchers injected 0.4-/*L samples of alcohols into a 20-L chamber containing the 12-sensor head and heated to 350 °C. The
vessel was purged with air and allowed to stand 45 minutes between injections. At these 5-ppm concentrations, electrical conductances of the sensors assumed a certain value after three minutes. These values were taken as the weighted average of individual partial conductances for each alcohol. In "training sessions/' the Warwick investigators "taught" the system what weight to assign to each partial conductance in working back from the total conductance. Results to date are encouraging, but further work is needed. The system sometimes comes up with a partial conductance considerably less than the ideal 1.000 w h e n an alcohol is present and somewhat greater than 0.000 when it is not. Stephen Stinson
New company launches STM instrument If ever a new instrument company appeared to be off to an auspicious start, TopoMetrix Corp., of Sunnyvale, Calif., would seem to be it. Visitors to the Pittsburgh Conference & Exposition on Analytical Chemistry & Applied Spectroscopy in Chicago early this month had a chance to view the company and its first product, a scanning probe microscope system. First the management. Founded last October to design, manufacture,
and market scanning probe microscopes worldwide, the company was started by Jack M. Gill, now chairman of TopoMetrix, a former director of research and engineering at Varian Aerograph, a senior executive at Spectra Physics, and founder of a leading venture capital firm; Paul E. West, now a vice president of TopoMetrix and chief technical officer, who built one of the world's first scanning tunneling microscopes during postdoctoral work un-
TopoMetrix's TMX 2000 scanning probe microscope system 24
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der California Institute of Technology chemistry professor John D. Baldeschwieler; and David J. Ray, now TopoMetrix's vice president of engineering, a 20-year career officer in the U.S. Air Force working in instrumentation development labs. Among those appointed to the board of directors is Robert Finnigan, founder and currently vice chairman and senior vice president of Finnigan Corp., and Klaus Derge, a senior vice president of Spectra Physics and currently responsible for all international operations, with headquarters in Darmstadt, Germany. Baldeschwieler will head a scientific advisory council. Second the product. The TMX 2000 scanning probe microscope system can create high-resolution, three-dimensional images of objects as small as individual atoms, under ambient, nondestructive conditions. The instrument is actually a product family with interchangeable stages to allow the analyst to change easily between analytical modes. The initial product includes three imaging modes: scanning force (SFM), scanning tunneling (STM), and large sample scanning tunneling (LSTM). The SFM stage, which is sometimes called an atomic force microscope, is used for images of either conductive or nonconductive surfaces; the STM stage is used for conducting and semiconducting surfaces; and the LSTM is used for samples up to 6 inches in diameter, such as semiconductor wafers. The TMX 2000 is priced at about $70,000. And third the market. Gill calls the existing market a "gee-whiz market" for R&D, with some 1000 instruments in existence worldwide, a third of them homemade. But a market is emerging for real applications and routine use in materials science and semiconductor work, he says. And he expects there to be a future market for quality control and routine analytical work. Putting numbers to these projections, Gill notes that the market in 1987 was perhaps $200,000. In 1990, it had grown to $20 million. By the late 1990s, Gill figures, the annual market will have grown to $500 million. SPM is a technique needed in more than 20,000 labs, he says. James Krieger
