Lying at the heart of the technique is a laser-irradiated metal nanosphere. The 60–80 nm diameter gold particle behaves as an optical antenna and provides enough field enhancement to detect the fluorescence from a single molecule.

The team's current set-up delivers a diffraction-unlimited spatial resolution of around 50 nm, which is sufficient to identify individual proteins. What's more, by replacing the spherical nanoparticle with a nanorod, it may be possible to push the optical resolution to less than 10 nm.

"This is in the works," Lukas Novotny of the University of Rochester's Institute of Optics told "We are able to fabricate gold-nanorod antennas and are performing first experiments."

The group's microscope design (see diagram) features an array of operating modes including near-field, wide-field and confocal imaging. In addition, the instrument can perform scanning force microscopy (SFM).

"One of the key advantages of our apparatus is that it provides simultaneous chemical and topological information," explained Novotny. "The high-resolution optical image allows us to identify individual constituents, such as proteins, while the SFM data can be used to investigate structural and mechanical properties of the membrane."

Novotny and his colleagues are interested in whether certain proteins act alone or require a "friend" to perform a given function. Using their instrument, the scientists perform so-called co-localization experiments – tagging two different proteins with different fluorescent labels and then imaging the membrane surface to determine any correlation between the distributions of the highlighted molecules.

The researchers presented their work in a special issue of Nanotechnology.