The study by researchers at Rice University could pave the way for mass produced single molecule sensors and could have significant applications in pharmaceutical lab-on-a-chip technologies.

"I would hope that this would be useful in small molecule assays and integrated into lab-on-a-chip devices. I think that this could be of real benefit in applications where extreme sensitivity of detection of well-known analytes is required," said Douglas Natelson, lead researcher and Professor of Physics and Astronomy at Rice University.

"In principle, we think the design may allow us to observe chemical reactions at the single-molecule level."

The experiment consisted of making measurements on a nanoelectronic device constructed from two small gold electrodes separated by a tiny gap. The researchers then used an electric current and measured conduction through the gap, which was built in such a way as to only allow one or two molecules to contribute to the conduction.

When this occurs, an "optical fingerprint" is associated with the molecule and the type of molecule can be identified. Other properties such as changes in position and rotation can also be measured.

"I estimate that it may be five years away from practical applications, though that could get shorter with sufficient investment of time and resources. The biggest hurdle to overcome right now is that our electrodes are made from gold."

Natelson said gold has benefits (it's relatively biocompatible, easy to pattern, has a very well studied surface chemistry), but also has drawbacks.

"At the atomic scale at room temperature gold is continually moving around and annealing, which is not so good for molecular scale devices' long-term stability. Other metals need to be examined, and we have some alternatives in mind," he said.

Other applications of the technology could be to get a clearer picture of nano-devices. They can currently only be seen with specially designed microscopes, but even they are still not sensitive enough to provide a clear picture of the object. The multimodal sensor developed at Rice would provide researchers with more information by combining optical and electrical measurements.

The single molecule sensor research was a result of collaboration between Professor Natelson's team, which specialises in observing the electronic and magnetic properties of nanoscale objects, and Rice's Laboratory for Nanophotonics (LANP), where the electronic and optical testing was performed. The results of the combined study is scheduled to appear in Nano Letters.

"Our latest results confirm that we have the sensitivity required to measure single molecules," said LANP Director Naomi Halas, Professor of Electrical and Computer Engineering and Professor of chemistry. "That sensitivity, and the multimodal capabilities of this system, gives us a great tool for fundamental science at the nanoscale."