Nano Lett.http://doi.org/hpx (2012)

The strong enhancement of light fields by surface plasmons in metallic nanostructures has been widely used for label-free molecular-sensing applications down to the single-molecule limit. A significant advance in the capability of such sensors has now been achieved by Carsten Sönnichsen and colleagues, who demonstrate single-molecule detection with high-temporal resolution by measuring small shifts in the plasmon resonance of a single gold nanorod when a protein binds to its surface. The experimental set-up is straightforward and involves measuring the light scattered by a gold nanorod. Because the nanorods are kept stationary within a glass capillary, any changes in plasmon resonance can be tracked on the millisecond scale. This way, the authors could conclusively identify several single-molecule binding incidents of the blood plasma protein fibronectin. By varying the nanorod size the sensitivity could be further enhanced towards the detection of smaller molecules. Even though the identification of proteins in mixed solutions has not been shown, such experiments could represent a valuable strategy towards resolving the dynamics of protein binding events on surfaces.