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Nanostructures eyed to identify biomolecules

Posted: 23 Apr 2003 ?? ?Print Version ?Bookmark and Share

Keywords:semiconductor chips? biomolecules? bionems? nanoelectromechanical systems? ic?

Two research groups are collaborating on an attempt to find a general solution to the problem of identifying biomolecules.

Rather than looking at the specific biomolecular behavior of a given organism in the hope of finding a unique chemical response system, researchers at the California Institute of Technology and the Massachusetts Institute of Technology are taking a new approach that is based on arrays of nanometer-scale cantilevers.

The idea is to study the dynamics of the cantilevers when immersed in an aqueous solution containing biosystems. Through computer simulation and actual experiments, the researchers hope to identify a unique dynamic signature in the response of the cantilevers to a specific organism. The results of the project hopefully will be used to advance the emerging field of biofunctionalized nanoelectromechanical systems (BioNEMS).

MIT's Raul Radovitzky is working on numerical methods for simulating cantilever response on supercomputers, while Mark Paul and Michael Cross at Caltech are studying the interface between biological and physical systems as part of the Caltech Initiative in Computational Molecular Biology.

Researchers on the CMB project are evolving BioNEMS by studying the relation between theory and simulation on the one hand and laboratory research in molecular biology on the other. While that represents a common technique in the physical sciences, it is a novel approach in molecular biology.

Nanoelectromechanical systems, or NEMS, are a critical technology in this effort, since they can realize physical systems on the same scale as biological systems. While NEMS might be viewed as an evolution of MEMS technology, some fundamental differences stem from discontinuities created by physical scaling.

A typical MEMS component might be a micron-sized rotor or other scaled-down mechanical part. NEMS are being built with parts on the scale of around 100nm, which requires a good deal more engineering expertise. Physical systems on this scale are very different from micron-scaled MEMS parts. In particular, the mechanical response times of nanometer sensors and actuators are similar to that of electronic circuits. For example, nanometer-scale cantilevers vibrate at frequencies between 1- and 15GHz. That speed of response opens many new electromechanical possibilities.

So far, the most successful NEMS components in biological applications have been an adaptation of chemical-force probes that respond to specific chemicals in a solution. This type of component was adapted from atomic-force microscope probes, which are being used by nanotechnologists for inorganic molecular-scale system fabrication.

NEMS promise to make a contribution to RF circuit designs by offering high-quality resonator components that are difficult to attain with integrated circuits. However, there are some difficult hurdles that must be overcome before their performance levels can be realized in practical systems.

One built-in problem is the fact that thermal noise in the NEMS part itself-that is, the mechanical vibration of its constituent molecules-easily disturbs the small signal obtained from it. That makes the design of sensitive signal transducers highly challenging. Another difficult factor is getting reproducible and reliable parts at such small dimensions.

- Chappell Brown

EE Times

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