Week of August 29, 2005

DNA buckyballs

Drug delivery -- the ability to target drugs to specific parts of the body -- is a major focus of nanotechnology research. The goal is to increase the effectiveness and decrease the toxicity of drugs used to treat diseases like cancer. One approach is to create nanoscale containers that carry minuscule amounts of substances.

Researchers from Cornell University have created branched molecules that combine DNA, which is attracted to water, and polystyrene, which is repelled by water. They found that in water the molecules assemble into buckyballs -- hollow spheres made up of hexagons and pentagons. The spheres measure 400 nanometers in diameter.

In addition to delivering drugs, the DNA buckyballs could be used as nanoscale test tubes to study minute amounts of substances.

(Self-Assembly of Nanobuckyballs from Dendrimer-like-DNA-Polystyrene Amphiphiles, American Chemical Society 2005 annual meeting, Washington DC, August 28, 2005)

Using light to measure force

Micromechanical sensors that measure physical forces like acceleration usually require that electronic circuits read what microscopic mechanical devices are doing. Researchers from Rensselaer Polytechnic Institute and Translume Inc. have made a displacement sensor that uses light rather than electricity to keep tabs on microscopic movements.

The prototype sensor is made from a single piece of glass and can detect movements as small as 50 nanometers, which is more than a thousand times smaller than the width of a human hair.

Sensors that transmit their signals using light could be used in environments that usually damage electronics, including space, where high levels of radiation can interfere with readings and degrade electronic equipment.

(Integrating Optics and Micro-Mechanics in a Single Substrate: a Step toward Monolithic Integration in Diffuse Silica, Optics Express, August 22, 2005)

Observing neurons in their natural habitat

Researchers from Stanford University have produced a very small version of the endoscope, a common medical device used for probing inside the body. The handheld device makes it possible to see individual nerve cells at work inside living brains.

The portable microendoscope produces clear images at the cellular level using two-photon fluorescence, a technique normally used by scientists to study the molecular makeup of materials.

The device can be used to study how diseases like Alzheimer's affect nerve cells and how the actions of individual nerve cells contribute to an animal's behavior.

(In Vivo Brain Imaging Using a Portable 3.9-Gram Two-Photon Fluorescence Microendoscope, Optics Letters, September 1, 2005)

Small-world thresholds by the numbers

Not only is it a small world, but many small worlds. In recent years scientists have figured out much of the mathematics underpinning network phenomena like six degrees of separation. All manner of networks, from the Internet to social networks to cellular interactions, exhibit small world behavior, meaning that any one node can reach any other node through a relatively small number of others.

Researchers from the Catholic University of Leuven in Belgium, Kings College London in England, the Institute for Scientific Interchange in Italy, and the University of Hasselt in Belgium have put together a network model that shows critical thresholds in these networks. A critical network threshold is a level of connectivity that causes a network's behavior to change abruptly, like when a disease becomes an epidemic or a power grid is overloaded and shuts down. The key to finding the critical thresholds is examining the strength of the connections to big hubs relative to the connections among smaller nodes.

The model could be used to study and better control natural network phenomena like diseases and artificial networks like the Internet and power grids.

(Trading Interactions for Topology in Scale-Free Networks, slated for publication in Physical Review Letters)

Bits and pieces

An image processing technique sorts out images from a set of tumbling, spinning, shaking cameras in real-time; a light-sensitive surface changes at the molecular scale to allow move droplets uphill; a hologram replaces several components of liquid crystal displays.

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