- Number 340 |
- June 27, 2011
Sharpening the plasmon nanofocus
By placing a palladium
nanoparticle on the focusing tip
of a gold "nanoantenna," they
were able to clearly detect
changes in the palladium's
optical properties upon
exposure to hydrogen.
Plasmonics is one of the hottest fields in technology today. Electronic surface waves called plasmons can be generated by confining electromagnetic waves shorter than half the wavelength of incident light, for example at the interface between gold nanostructures and insulating air.
If the oscillation frequency of the plasmons and the electromagnetic waves matches, the electromagnetic field can be “nanofocused” within a few hundred cubic nanometers. Nanofocusing can be used with dark-field microscopy to detect low concentrations of biochemical agents, single catalysis in nanoreactors, and other processes. Plasmonic sensing is especially promising for detecting flammable gases like hydrogen, where electrical sensors pose safety issues because of possible sparking.
Researchers with DOE’s Lawrence Berkeley National Laboratory in collaboration with colleagues at the University of Stuttgart, Germany, reported the first experimental demonstration of nanofocusing to enhance gas sensing at the single-particle level in the journal Nature Materials. By placing a palladium nanoparticle on the focusing tip of a gold “nanoantenna,” they were able to clearly detect changes in the palladium’s optical properties upon exposure to hydrogen.
“Metallic nanostructures with sharp corners and edges that form a pointed tip are especially favorable for plasmonic sensing, because the field strengths of the electromagnetic waves are so strongly enhanced over such an extremely small sensing volume,” says Laura Na Liu, lead author of the Nature Materials paper, now at Rice University and formerly with the research group of Paul Alivisatos, Berkeley Lab’s Director, who led the work.“We have demonstrated resonant, antenna-enhanced, single-particle hydrogen sensing in the visible region and presented a fabrication approach to the positioning of a single palladium nanoparticle in the nanofocus of a gold nanoantenna,” says Alivisatos. “Our concept provides a general blueprint for amplifying plasmonic-sensing signals at the single-particle level and should pave the road for the optical observation of chemical reactions and catalytic activities in nanoreactors and for local biosensing.”
[Paul Preuss, 510.486.6249,