Week of October 31, 2005

Double-barreled nano printing

The ability to precisely position tiny amounts of DNA and other biological molecules is becoming increasingly important in studying diseases, finding new drugs and diagnosing illness. It is also key to the emerging practice of making nanoscale devices from biomolecules.

One challenge is figuring out how to rapidly deposit microscopic amounts of two or more substances in the same place.

Researchers from the University of Cambridge and Imperial College London in England have addressed the problem with an electrically controlled double-barreled nanopipette that can precisely place tiny amounts of two different biomolecules onto a surface.

They demonstrated the the device's fine control by making microscopic reproductions of paintings.

The barrel openings measure as small as 140 by 100 nanometers. Electrical voltage -- one barrel positive and the other negative -- causes biomolecules to flow out of one barrel. When the voltage is reversed biomolecules flow from the second barrel. The device deposits dots of material as small as 350 nanometers in diameter, which is about 15 times smaller than a red blood cell.

The advantage of the double barrels is being able to deliver two substances to the exact same spot, without having to precisely position a second nanopipette.

The technique could be used with more than two barrels; current fabrication methods make as many as seven.

(Two-Component Graded Deposition of Biomolecules with a Double-Barreled Nanopipette, Angewandte Chemie International Edition, published online October 25, 2005)

Security through obfuscation

In the world of computer security the name of the game is access, or more specifically preventing access. If you don't have the right password and/or certificate and/or token, you can't get in the door.

Researchers from the University of Texas at Austin are trying a different approach -- obfuscated databases and group privacy. Under their system, anyone can get in the door, but you can only get information that you already know something about.

A database query, for instance, consists of some piece of information unique to the record sought. For example, plugging in your name and frequent-flier number would allow you to retrieve a statement of your frequent-flier miles. But instead of using your name and number as part of an authentication scheme -- to prove that you are you -- they are simply part of the database record itself.

This removes the need for an authentication mechanism to maintain (and protect) every user's name and frequent-flier number. The system is secure because it is virtually impossible to guess the astronomical number of combinations of names and numbers, even with a very powerful computer.

(Obfuscated Databases and Group Privacy, 12th ACM Conference on Computer and Communications Security (CCS 2005), November 7-11, Alexandria, Virginia)

Better light switches

A pair of research papers promises improvements in optical modulators, the light switches that encode data into light beams for data communications. One could lead to a 100-fold speed up of telecommunications and the other provides a relatively inexpensive way of building optical modulators into silicon computer chips.

Researchers from the University of California at Santa Barbara, NASA and the Georgia Institute of Technology used a powerful electric field to push a quantum well optical modulator to nearly 4 terahertz, or trillion times per second. Quantum wells are made of extremely thin layers of semiconductor that confine electrons to a plane.

At such high frequencies relatively low-power communications-wavelength light beams can be used to control each other, opening the way for much faster data flow through fiber-optic communications lines.

Meanwhile, researchers from Stanford University and Hewlett-Packard Laboratories have made an optical modulator from a stack of multiple quantum wells made from relatively inexpensive silicon and germanium. Existing similar devices use more expensive compound semiconductors that are not easily integrated with silicon computer chips.

This second advance promises cheap, miniaturized communications devices like the switches that route traffic in telecommunications networks.

(Quantum Coherence in an Optical Modulator, Science, October 28, 2005 and Strong Quantum-Confined Find Stark Effect in Germanium Quantum-Well Structures on Silicon, Nature, October 27, 2005)

Molecule walks this way

Scientists making molecular-scale mechanical devices have been mining the past for ideas. This makes sense because things move much faster at the molecular scale. The enhanced speed opens up new possibilities for mechanical computation devices like the ancient abacus.

Researchers from the University of California at Riverside and Kansas State University have created a two-legged molecule that can walk in a straight line on a flat copper surface without a track.

The structure of the molecule ensures that only one leg at a time is in contact with a surface, and as the leading leg lands the trailing leg lifts from the surface and swings forward. Copper is a crystal, and a copper surface has three directions of symmetry, or orientations where copper atoms line up. Energy supplied by a heat source or a nudge from microscope probe starts the molecular walker (representing an abacus bead), which then follows one of these directions of symmetry (representing an abacus line).

Armies of the molecular walkers could be used to store large amounts of data in relatively small spaces or to do blazingly fast abacus-style computation.

(Unidirectional Adsorbate Motion on a High-Symmetry Surface: "Walking" Molecules Can Stay the Course, Physical Review Letters, October 14, 2005)

Bits and pieces

A study shows that attaching molecules to the outsides of single-walled carbon nanotubes make the tubes less toxic to cells; a molecular motor attached to a surface spins in only one direction; a carbon nanotube field-effect transistor brings spintronics a step forward.