Rice scientists make breakthrough in single-molecu...( HOUSTON Feb. 6 2008 -- In a study th...)

HOUSTON, Feb. 6, 2008 -- In a study that could lay the foundation for mass-produced single-molecule sensors, physicists and engineers at Rice University have demonstrated a means of simultaneously making optical and electronic measurements of the same molecule.

The research, which is available online, is slated to appear in an upcoming issue of the journal Nano Letters. The experiments were performed on a nanoelectronic device consisting to two tiny electrodes separated by a molecule-sized gap. Using electric current, the researchers measured conduction through single molecules in the gap. In addition, light-focusing properties of the electrodes allowed the researchers to identify the molecule by a unique optical fingerprint.

"We can mass-produce these in known locations, and they have single-molecule sensitivity at room temperature in open air," said study co-author Douglas Natelson, associate professor of physics and astronomy and co-director of Rice's Quantum Magnetism Laboratory (QML). "In principle, we think the design may allow us to observe chemical reactions at the single-molecule level."

While scientists have used electronic and optical instruments to measure single molecules before, Rice's system is the first that allows both simultaneously -- a process known as "multimodal" sensing -- on a single small molecule.

The research sprang from a collaboration between Natelson's group -- where the electrodes were developed -- and Rice's Laboratory for Nanophotonics (LANP), where the simultaneous electronic and optical testing was performed. In research published last year, the two groups explained how the electrodes focus near-infrared light into the molecule-sized gap, increasing light intensity in the gap by as much as a million times. The increased intensity allows the team to collect unique optical signatures for molecules trapped there via a technique called surface enhanced Raman spectroscopy (SERS).

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