Week of November 7, 2005

Holograms organize nanowires

During the past few years scientists have gotten good at using holograms to move and manipulate microscopic objects. The methods, however, are usually limited to spherical objects, which include cells and microbes.

Researchers from Harvard University and New York University have found a way to use holographic optical traps to move and manipulate long, thin semiconductor nanowires. Holographic optical traps are computer-controlled holograms focused through a microscope onto objects floating in liquid.

The method can be used to move, rotate, cut and fuse semiconductor nanowires. The researchers demonstrated the technique by constructing a rhombus from cadmium sulfide nanowires.

The work is a step toward a key ability: being able to assemble many complex, three-dimensional nanowire structures at once. This would enable the manufacturing of new forms of optical and electronic devices like fast, high-capacity computer memory chips.

(Manipulation and Assembly of Nanowires with Holographic Optical Traps, Optics Express, October 31, 2005)

DNA delivers anti-cancer drug

Nanotechnologies that tap DNA have heated up lately, especially in the drug delivery field.

Researchers from Harvard University and the Massachusetts Institute of Technology have reported the latest in a string of nanotech advances to fight cancer. The anti-cancer therapy combines polymer nanoparticles that contain an anti-cancer drug with short strands of DNA or RNA that bind to a protein found on the outside of prostate cancer cells.

The polymer is biocompatible and breaks down over a controllable amount of time to release the drug. The researchers tested the nanoparticle-DNA treatment on prostate cancer cells inside a microfluidic device designed to mimic conditions inside the body. They found that the anti-cancer drug was taken in by the cancer cells but not by surrounding healthy cells.

Other scientists have recently made RNA nanoparticles that deliver anti-cancer drugs to cancer cells, DNA-polystyrene spheres that could be used for drug delivery, and polymer nanoparticles that contain an anti-cancer drug and folic acid, which is readily absorbed by cancer cells.

(Cancer Nanotechnology: Drug Encapsulated Nanoparticle-Aptamer Bioconjugates for Targeted Delivery to Prostate Cancer Cells, 13th European Cancer Conference (ECCO), Paris, October 30-November 3, 2005)

Tiny sensors tracked

The continuing miniaturization of electronic devices has reached a point where tiny, inexpensive sensors scattered throughout an environment are becoming practical. Networks of sensors could be used to monitor aspects of the environment, collect data for scientific research and track troop and vehicle movements for military applications.

Finding ways for the diminutive devices to locate and communicate with each other efficiently is a particularly active area of study.

Researchers from Vanderbilt University have come up with a way to determine individual sensors' positions using the radiowaves sensors use to communicate with each other.

The method measures radio signal interference across several sensors in a network to determine the strength of a given sensors' signal. The method works in networks of as few as six sensors.

The researchers' prototype located sensors to within three centimeters at ranges of up to 160 meters.

(Radio Interferometric Positioning, 3rd ACM Conference on Embedded Networked Sensor Systems (SenSys), San Diego, November 2-4, 2005)

Sensors net tree data

Scientists are beginning to use networks of tiny sensors to collect data that would be impractical to gather using traditional methods.

Researchers from the University of California at Berkeley and Intel Research have deployed a sensor network around a 70-meter tall redwood tree to study the microclimate around the tree and evaluate real-world use of sensor networks.

The one-inch-diameter sensors took readings of temperature, humidity, barometric pressure, direct sunlight and ambient light every five minutes. Thirty-three sensors were deposited on the tree at 2-meter intervals. The "macroscope" experiment ran for 44 days, and yielded 820,700 pieces of information, which was 49 percent of the data points the network was set to try to measure.

The study yielded information about the spatial and temporal variations in the microclimate around the tree. It also brought to light some ongoing technical challenges: positioning the sensors, monitoring their status and analyzing large amounts of data.

(A Macroscope in the Redwoods, 3rd ACM Conference on Embedded Networked Sensor Systems (SenSys), San Diego, November 2-4, 2005)

Bits and pieces

A software system uses Web documents to sort out people who have the same common names; neural network software uses video images of reefs to automatically classify live coral, dead coral and non-coral areas; interferometric measurements provide a detailed view of slow light traveling through silicon photonic crystals.