science/ technology concentrates Space Flight Center, Greenbelt, Md., says in miniature electronic devices, Universithis is thefirsttime anyone has used an ty of Pittsburgh chemistry professor John X-ray signature to identify the composition T. Yates Jr. says. Both the defects and of an asteroid. Knowledge about Eros' ele- any fullerene end caps that may be Microcantilever senses mental makeup will help scientists under- present on the tubes are vulnerable to oxstand where the asteroid came from— idation, providing a means to study these traces of cesium whether ifs a chunkfromthe surface or sites. Yates, chemistry and physics proA new sensor consisting of a microcanti- the center of a larger body, for example.^ fessor Richard E. Smalley at Rice University, Houston, and four of their graduate lever coated with an ion-selective selfstudents have now designed an easy way assembled monolayer detects parts-perto oxidize nanotubes in situ with ozone at billion concentrations of cesium ions in Fluorescent probes 2+ the presence of high concentrations of could assay Zn in cells 25 °C [f. Am. Chem. Soc, 122, 2383 (2000)]. The reaction converts carbon atpotassium and sodium ions. Staff scientist Reza Dabestani, postdoctoral re- Fluorescent probes that are excited by oms adjacent to the defect sites and at the searcher Hai-Feng Ji, and coworkers at visible light have been shown to selec- end caps into surface-bound esters and quiOak Ridge National Laboratory coated a tively detect Zn2+ at physiological pH [An- nones, providing carbonyl sites for further commercially available microcantilever gew. Chem. Int. Ed., 39,1052 (2000)].Thefunctionalization of the tubes, if desired. with a cesium recognition agent—a thiol compounds are expected to offer a useful The oxidation can be reversed by raising derivative of a calix[4]benzocrown-6— tool for measuring Zn2+ concentration in the temperature to about 600 °C, releasand showed that the sensor detects nano- living cells. The azacrownfluorone probes ing C0 2 and CO. The researchers use molar concentrations of cesium ions (shown) were developed by a University of Fourier-transform infrared spectroscopy [Chem. Commun., 2000,457]. "The sen-Tokyo research team led by Tetsuo Naga- to track and measure the extent of oxidasitivity of the sensor is at least two orders no, professor of molecu- tion, which indicates the concentration of of magnitude better than currently availCH3 lar pharmaceutics and defects in the original nanotube.^ able ion-selective electrodes," Dabestani /^N-"X bioorganic chemistells C&EN. The coated microcantilever \ / try. Fluorescent bends when cesium ions complex with H3C-N N-CH3 probes for Zn2+ Electrodes grow forest the recognition agent. The bending is \^N^^ had previously of carbon 'trees' measured by monitoring the position of a been developed, laser beam reflected off the top of the mibut they are un- A micrometer-scale forest of carbon crocantilever onto a photodiode. The suitable for mea- "trees" (shown) grows up autocatalytically team suggests that the methodology can suring zinc con- from the surface of graphite electrodes be applied to the detection of a wide varicentrations in bi- treated only with methane using extreme ety of metal ions of chemical, biological, ological samples conditions of chemical vapor deposition, and environmental importance. "We are x = H or ci in vivo because according to Pulickel M. Ajayan, an assocurrently synthesizing molecular recogthey either must ciate professor in the department of matenition agents containing different size be excited at ultraviolet wavelengths rials science and engineering at Renscavities capable of complexing different (which can damage cells) or they operate selaer Polytechnic metal ions to measure low levels of these at a physiologically incompatible alkaline Institute, Troy, ions in groundwater and/or waste pH. To fashion the new probes, the team N.Y., and his colstreams," Dabestani says.^ designed and synthesized the fluorophore, leagues [Nature, coupling it directiy to a macrocyclic poly404,243(2000)]. amine. The fluorophore's 2,7-dichloro deThe newly deposNEAR receives an X-ray rivative also was prepared and similarly ited carbon surcoupled. In various experiments, the team bonus from solar flares faces restructure has shown that the fluorescence intensity to form narrow The fortuitous timing of two solar flares of both probes increases dramatically as cones of carbon has allowed NASA's Near Earth Asteroid the concentration of zinc is raised. Fluothat taper away affected by high concenRendezvous (NEAR) spacecraft to make rescence is not from the electrode surface when the + + 2+ 2 thefirst-everX-ray study of an asteroid. trations of Na , K , Ca , or Mg *, suggestteam treats graphite electrodes to a se2+ Theflares,which occurred on March 2, ing that the probes are specific for Zn .^ ries of rapid cycles of heating in a highproduced a blast of X rays that struck the pressure atmosphere of helium and surface of NEAR's destination, the asmethane. The cones get taller with each Opening a window on teroid Eros. At that time, NEAR was successive heating cycle until they reach 180 milesfromthe asteroid. The elements nanotube behavior a height of a few hundred micrometers, on Eros' surface produced a correspondwhen the tops of the cones take on a finer, ing excitation emission, which NEARs The ordered carbon structure of single- more treelike morphology. Optical microsX-ray/gamma ray spectrometer (XGRS) walled nanotubes (SWNTs) is marred by copy reveals that the structures are hollow, recorded. From the spectral fingerprint, defect sites of missing carbon atoms that especially near their bases. "Our results scientists identified magnesium, alumi- interfere with the nanotube's desired show that carbon surfaces can be tailored num, silicon, and iron. Calling the observa- electrical properties. Hence, the ability to while they are growing simply by controltion 'Very exciting," Jacob Trombka, XGRS detect and quantify the defects is crucial ling the rate of depositionfromthe vapor science team leader at NASA's Goddard to the design of nanotubes and their use phase," the researchers write.^
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