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APS physics tip sheet #57

News from the American Physical Society

American Physical Society

Catching the Flu - One Virus at a Time
F. V. Ignatovich and L. Novotny
Physical Review Letters (forthcoming article, available to journalists on request)

Even a single flu virus can't sneak by a new nanoparticle sensor developed at the University of Rochester in New York. Researchers at the university's Institute of Optics relied on a highly sensitive laser interferometer to detect individual flu viruses, 5 nanometer gold particles, and 10 nanometer polystyrene particles that were swept past a laser beam in a stream of water. Unlike conventional detection techniques, the laser interferometer sensor does not require that small particles be specially treated or immobilized on a surface for detection. It is also much faster than most other methods, detecting particles at rates of a thousand a second or more. The researchers expect that their detection scheme will lead to effective screening for microbes and biowarfare agents as well as methods for tracking particles inside cells and monitoring water and air contamination.

Narrow Channels Speed Drying, Even When it's Humid Out
J. C. T. Eijkel et al.
Physical Review Letters (forthcoming article, available to journalists on request)

Objects can dry hundreds of times faster than previously thought, even in humid conditions, with the help of thin grooves with sharp edges, according to a new report by researchers from the University of Twente in the Netherlands. They experimented with an array of trapezoid-shaped nanochannels (4 mm long, about 72 nm deep, and between 2 and 30 micrometers wide) etched in glass. The researchers found that the sharp corners of the grooves helped channel water quickly to the edges of the glass, enabling the glass to dry hundreds of times faster than without the sharp-cornered channels. The thinnest channels dried fastest, and relative humidity did not affect the drying rate, up to relative humidity of more than 90%. The results could be useful for designing more efficient heat pipes for cooling chips, or possibly in applications where rapid drying is desired, such as clothing.

Electronic Switches to get (nano)Tubular
Y.-W. Son et al.
Physical Review Letters 95, 216602 (2005)

Carbon nanotubes may make useful electrical switches, according to the theoretical predictions of a collaboration of American and Korean scientists. As the size of electronic devices continues to shrink and the importance of nanoscale technology grows, a top objective in research is to create nanoscale integrated circuits. Switches that regulate electrical signals are essential for this. Previous research showed that metallic carbon nanotubes would not make effective switches because their electrical properties could not be regulated with electrical fields, so they could not be turned on and off. According to the new study, however, adding impurities such as boron or nitrogen to a metallic carbon nanotube makes the electrical properties sensitive to electric fields. As a result, changing the fields near a nanotube can crank the resistance up a thousands times or more and switch an electrical signal off. The theory provides a strong impetus for research using carbon nanotubes as ultra-small electronic switching devices.

A Microscope that Sees without Looking
T. Kalkbrenner et al.
Physical Review Letters 95, 200801 (2005)

A new type of microscope overcomes some of the limitations of optical imaging techniques by looking at how samples affect a tiny antenna, rather than looking at the sample itself. Most optical microscopes create images by collecting photons reflected from a surface. But when samples get very small or have tiny features, the limitations of optics kick in and prevent the imaging of objects smaller than a micron or so across. Instead of shining a light on a sample, a team of Swiss and German researchers have found that they can take pictures of a small sample by illuminating a tiny, gold antenna placed near a surface. The antenna emits different signals depending on the sample structure. It's much like sweeping a metal detector over the ground to map out the location of a buried pipe - the rising and falling pitch of the metal detector results because the hidden metal changes the way the detector circuit reacts. Conventional optical microscopy, on the other hand, is more like radar, which would locate a buried pipe by bouncing radio waves off of it. The microscope in the new study consists of an antenna made from a single particle of gold, 100 nanometers in diameter or smaller, mounted on the tip of a glass fiber that is scanned over the sample at a height of 5 to 10 nanometers. The system provides detail of structures as small as a few hundred nanometers across, but the researchers believe the technique has the potential to be refined to image features a hundred times smaller.


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