October 2005

Amazing nanotech in Boston: Weighing DNA, digital heat flow, electromechanical butterfly images

AVS press luncheon to feature latest breakthroughs in the world of small

How does a scientist weigh something as small and light as a DNA strand? What seldom used electro-mechanical property in biological tissue has enabled some of the best-ever submicroscopic images of butterfly wings? How does heat flow at the quantum scale?

These and other questions will be addressed on Monday, October 31, 2005, from 1-2 PM, at a press luncheon for the 52nd AVS International Symposium & Exhibition in Boston. The luncheon will take place in the Exhibitor Workshop area of Exhibit Hall D of the Hynes Convention Center (900 Boylston Street). The entire symposium takes place between October 30-November 4, 2005. The meeting will feature over 1300 papers and posters, with at least 3,000 expected attendees.

Reporters interested in attending the luncheon should fill out the registration form at http://www2.avs.org/symposium/boston/pressroom/regform.html . A web pressroom on the meeting is located at http://www2.avs.org/symposium/boston/pressroom.html

The following is a summary of some of the results to be discussed at the luncheon:

WEIGHING DNA AND OTHER NEW DEVELOPMENTS IN THE WORLD OF NANOSCALE DEVICES
Speaker: Harold Craighead, Cornell University

Nanoelectromechanical systems (NEMS) technology---electronic and mechanical devices with dimensions at the nanometer scale---is especially valuable for sensing single molecules. Using small NEMS detectors makes analysis or detection faster, and requires only tiny amounts of sample material to make good measurements. But the main motivation is NEMS's much greater sensitivity in locating and identifying single biomolecules by measuring their masses. A typical NEMS sensor consists of an oscillating slab so small in size and mass that even if a single DNA molecule were to alight on it, the slab's resonant frequency (the vibration rate it maintains once set in motion) would shift measurably, enabling the researchers to determine the mass of the DNA.

Researchers at Cornell's Nanoscale Facility are optimizing the NEMS biosensor. They aim to use their sensitive device to catalog the contents of strands of DNA with lengths of about 1500 base pairs. In addition to this work, Craighead will describe other activities in his research group, which is perhaps best known among the general public for designing a tiny guitar, around the size of a red blood cell.

ELECTROMECHANICAL IMAGING OF BUTTERFLY WINGS AND OTHER BIOLOGICAL TISSUE
Speaker: Sergei Kalinin, Oak Ridge National Laboratory

Applying state-of-the-art technology to a seldom-exploited electromechanical property in biomolecules, Sergei Kalinin and Brian Rodriguez of Oak Ridge National Laboratory and Alexei Gruverman of North Carolina State University have demonstrated a nanometer-scale version of Galvani's experiment, in which 18th-century Italian physician Luigi Galvani caused a frog's muscle to contract when he touched it with an electrically charged metal scalpel. The new, 21st-century demonstration promises to yield a host of previously unknown information in a variety of biological structures including cartilage, teeth, and even butterfly wings.

Employing a technique named Piezoresponse Force Microscopy (PFM), Kalinin and colleagues sent an electrical voltage through a tiny, nanometer-sized tip to induce mechanical motion along various points in a biological sample, such as a single fibril of the protein collagen. The electromechanical response at various points of the sample enabled the researchers to build up images of the collagen fibrils, with details less than 10 nanometers in size. This resolution surpasses the level of detail that can be gleaned on those biostructures by ordinary scanning-probe and electron microscopes. The PFM technique exploits the well-known but infrequently used fact that many biomolecules, especially those that are made of groups of proteins, are piezoelectric, or undergo mechanical deformations in the presence of an external electric field.

The researchers have used the PFM technique to produce images of cartilage as well as enamel and dentin (found inside teeth). Besides providing images of biostructures on a nanometer scale, the new technique yields information about the electromechanical properties and molecular orientation of biological tissue. In recent work, the researchers even found unexpected piezoelectric properties in butterfly wings which enabled them to yield molecular-level images of wing structures.

** For more information and images, a lay-language paper by Sergei Kalinin is available at http://www2.avs.org/symposium/boston/pressroom/Sergey-PFM-davide_svkv2_.pdf

EXPERIMENTAL OBSERVATION OF "DIGITAL" HEAT FLOW
Speaker: Marc Bockrath, Caltech

The first observation of "digital" or quantized heat flow in a nanostructure at ambient conditions has been made by Caltech researchers using carbon nanotubes suspended between two electrodes. A new experiment carried out at Caltech furthers the effort to employ nanotubes as a conduit for removing unwanted heat from microcircuits. Carbon nanotubes, nanometer-wide cylinders made from rolled-up sheets of graphite, have a versatile array of mechanical, electrical, and magnetic properties. Their thermal properties should be just as valuable. Because phonons (the particle manifestations of heat flow) can move so freely in nanotubes, even ballistically (meaning that they refrain from scattering and travel in straight lines), the flow of heat in nanotubes should have quantum properties.

Indeed, Caltech scientist Marc Bockrath ([email protected]) and his colleagues have observed that heat conductivity in nanotubes can reach an ultimate limit to heat flow where heat conduction occurs in multiples of a quantum unit of heat flow. Phonons seem to move nearly as far as hundreds of nanometers (a long distance for nanoscopically sized objects) even at temperatures of 600 C. The phonons' mean-free path (the average distance they travel between collisions) should be even larger at room temperature. This, says Bockrath, underscores the fantastic potential of nanotubes as thermal conduits.