Harnessing Bio/Molecular Properties for Nanoelectronic Devices

2/13/2003 - 17-03r
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Developing nanosized electronic devices requires a comprehensive understanding of how electrical charges move across the molecules that make up the device. These molecules are clustered into small units. In order for such devices to work, these nanoscale clusters of molecules should "communicate" with each other at points known as junctions. This "communication" would occur through one or both sides of a metal contact, using an electronic signal that is transmitted from the molecule to the metal or vice versa. Consequently, the role of the metal-molecule contact can drastically affect the way device functions. The situation becomes even more complex if the molecules are in contact with two different kinds of metals, one on each side.

To study the electrical behavior of these metal-molecule contacts, scientists at the Naval Research Laboratory's Center for Bio/Molecular Science and Engineering in Washington, DC, have used a technique called a crossed-wire tunnel junction, which was specially designed to vary the nature of the metal-molecule contact at the two ends of the molecule. This approach demonstrated that a molecule can behave like a molecular diode when it is chemically linked at one end, while it exhibits the characteristics of a molecular wire when linked at both ends. These results show that the design features of a nanoelectronic device must carefully take into account how contact is made between the molecule and the metal surface.

An important but unresolved question related to nanoscale electronic devices is the amount of intermolecular coupling within a self-assembled, one-molecule-thick layer (monolayer) of molecular wires and what effect, if any, this coupling has on junction conductance. NRL scientists have studied charge transport across a metal-molecule-metal junction, consisting of molecular wires in a densely packed monolayer. The current-voltage characteristics in this study demonstrated that molecular wires connected in parallel act as separate, non-interacting conductance channels. These results indicate that it should be possible to make a nanoelectronic device using a very small number of molecules and the function of such a device would still be representative of the function of a single molecule. For instance, if a molecule shows memory or bistable states, the nanoelectronic device made from such molecules would also exhibit the same behavior.

Hybrid nanoelectronic devices consisting of biological components combine the superb molecular recognition properties and complex activities of biomolecules with the power of existing electrochemical, optical, magnetic, or mechanical technologies. Central to the development of such devices is the construction of interfaces that convert bio-molecular events into electronic signals.

Molecular recognition, signal transduction and detection of the signal are all necessary components of a biomolecular interface. The major obstacle to developing families of interfaces is the difficulty in identifying biomolecules in which these three functions are sufficiently independent to attain a high diversity in molecular recognition while keeping signal transduction and detection mechanisms constant.

Work at NRL has recently demonstrated that a peptide suitably attached to a surface via an electrochemically active molecule, exhibits a large change in potential when a chemical analyte binds to the peptide. These results could lead to the development of a bioelectronic sensor where binding a chemical agent on a molecular level can lead to an electronic signature. The development of high sensitivity, high density, nanoelectronic sensors using these principles is a distinct possibility.

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The U.S. Naval Research Laboratory provides the advanced scientific capabilities required to bolster our country's position of global naval leadership. The Laboratory, with a total complement of approximately 2,500 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 90 years and continues to advance research further than you can imagine. For more information, visit the NRL website or join the conversation on Twitter, Facebook, and YouTube.

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