Meeting Briefs

More than 9,000 papers were presented at last month's American Chemical Society national meeting in San Diego. Here are some highlights.

Pushing bacteria around

Bacterial cells are an appropriate size for use as templates for nanoscale structures, but first they must be made easily manipulable. Using Bacillus mycoides, a rod-shaped bacterium, postdoc Joseph D. Beck, chemistry professor Robert J. Hamers, and coworkers at the University of Wisconsin, Madison, have shown that they can controllably and reversibly manipulate live bacterial cells into a micrometer-scale gap between electrodes and detect them through changes in the electrical response (Nano Lett., published online March 17, http://dx.doi.org/10.1021/nl047861g). At sufficiently low voltages, the bacteria are captured gently enough that individual cells can be propelled along the electrode surface by liquid flow--all the way along the electrode and into the gap between two electrodes (shown). With a small electrode tapered to a point, individual cells can be captured and electrically characterized. The bacteria so manipulated are unharmed, as indicated by the presence of intact cell walls and active metabolic processes.

Videos of this process at http://www.news.wisc.edu/newsphotos/hamers.html.

Composite membrane for fuel cell

The fuel-cell design considered to be most promising for use in future zero-emissions vehicles is the proton-exchange membrane (PEM) fuel cell, which currently operates in the 60–80 °C range. Unfortunately, this cell is poisoned by trace amounts of carbon monoxide (about 10 ppm) that are inevitably present in the fossil-fuel-derived H₂ used as the cell's fuel. But there may be a way around that problem, according to chemistry professor Andrew B. Bocarsly of Princeton University and his colleagues. Operating the PEM cell at higher temperatures (120–150 °C) would help, but the proton-conducting polymer membrane at the heart of the cell has difficulty retaining water at these temperatures, and water retention is essential for good performance, he said. Bocarsly's solution is to use a modified membrane containing metal oxide particles such as TiO₂ that help the material retain water. The team showed that, with this composite membrane installed, the fuel cell performs better at 130 °C than at 80 °C, even when the hydrogen fuel is loaded with 500 ppm of CO.

DNA turned on by light

Support for the feasibility of using light to trigger DNA or RNA action with simultaneous spatial and temporal control comes from Alexander Heckel of the University of Bonn, in Germany. He and coworkers have shown that DNA that is nonfunctioning--because it incorporates nucleobases that have been modified with photolabile protecting groups--becomes functional when irradiated with light. According to Heckel, thymidine and deoxyguanosine modified with a photolabile group are unable to pair properly with their base complements. In one example, transcription of DNA that incorporates even one such thymidine is impaired because of the mismatch. Irradiation of that DNA, which cleaves the protecting group, repairs the mismatch and allows transcription to proceed. In another example, a short single-strand DNA that binds to and inactivates ∝-thrombin, a key player in blood clotting, is unable to do so when the protected thymidine is installed at positions involved in the binding. The DNA's activity is restored by irradiation. The use of light to control DNA function is not new, but here the modifications to DNA are at specific sites, ensuring binary behavior--on or off--Heckel told C&EN.

Nanofiber blood vessels

Each year, Americans undergo 1.4 million arterial bypass surgeries, wherein a doctor detours blood flow around a blocked blood vessel using a healthy vein taken from elsewhere in the body. But many bypass patients don't have veins hardy enough to withstand the procedure. A group led by Anthony Atala of Wake Forest University's Institute for Regenerative Medicine, Winston-Salem, N.C., has been working to create artificial blood vessels that are biomechanically similar to natural veins. Atala's group makes artificial veins by electrospinning polymer blends of collagen type I, elastin, and poly(D,L-lactide-co-glycolide) into nanofiber scaffolds. Not only does the electrospinning process allow the researchers to control the length and diameter of the artificial vein, but it also lets them add functional nanomaterials to the scaffold. Collaborator Richard Czerw has added a gadolinium magnetic resonance imaging contrast agent for in vivo monitoring of grafts. And coworker Grace Lim incorporated a light-activated anticoagulant into the scaffold using quantum dots that are covalently linked to heparin. The group is testing the electrospun blood vessels in animals.

X-ray vision aids fingerprint analysis

An X-ray fluorescence technique that can be used to image fingerprints based on elemental analysis of print residues is expected to become a valuable tool to complement traditional fingerprinting, according to Los Alamos National Laboratory chemists who developed the process. The method also can reveal chemical clues about food, explosives, and other materials recently handled by the person who left the prints. Traditional "dusting" for prints includes treating surfaces with powders, liquids, or vapors so that prints can be photographed. However, adding chemicals can sometimes alter prints and damage prospects for further analysis. The LANL team, led by Christopher G. Worley, developed the nondestructive X-ray method to scan surfaces and image fingerprints using, for example, sodium, potassium, and chlorine from salt in perspiration. Chemical treatment can still be used to enhance an image, Worley noted, such as the print shown, which was dusted with iron-containing powder. Prints can be detected by the method even when the prints result from lotion, soil, or saliva on the hands.