Shedding Light on a Mystery of Raman Signal Enhancement
Led by the Molecular Foundry's Jeff Neaton, researchers have unraveled a mystery behind surface-enhanced Raman spectroscopy---a detection method useful for analyzing artwork and anthrax alike.
Raman spectroscopy uses light scattered by vibrations from atoms to provide scientists with a unique signal for a given molecule. For isolated molecules or nanoscale materials, this signal is usually too weak to be detected. Surface-enhanced Raman spectroscopy capitalizes on the enhancement of a Raman signal from a molecule placed on a rough metal surface. Like an array of antennas, the metal amplifies a signal billions of times or more, enabling single-molecule detection.
In this study, the team developed quantum-mechanical calculations to study changes in Raman signal intensity caused by the chemical binding of benzene thiol on a gold surface. Vibrations from this molecule cause electrical charge to "slosh" from a molecule to the metal, triggering signal enhancement.
Using this model, other researchers can interpret chemical contributions to signal enhancement in their own experimental data. This strategy can be extended to other interfaces involving a molecule and a metal, such the flow of electrical charge or heat through nanoscale interfaces and molecular junctions.