NanoLett.http://doi.org/tzx(2014)

Credit: © AMERICAN CHEMICAL SOCIETY

A widely used technique to enhance the spatial resolution in fluorescence microscopy relies on the simultaneous use of a primary laser beam, which excites the fluorescent object to be imaged, and a secondary doughnut-shaped beam, which inhibits the emission of the object far from the point excited by the primary laser. This approach, which is named stimulated emission depletion microscopy, has a resolution limit that improves with the intensity of the secondary beam; hence very intense lasers are usually required to achieve the best performance. Yannick Sonnefraud and colleagues now show that plasmonics can help to overcome this constraint. The plasmon resonance generated in a thin gold coating surrounding silica spheres doped with fluorescent dyes is used to locally enhance the intensity of the secondary laser. The power density of this beam can be reduced by a factor of four with respect to that used with non-coated spheres, while obtaining a similar inhibition effect on the dye emission — that is, a similar spatial resolution.