Giant electromagnetic (EM) field enhancement via specifically designed metal nanostructures plays a key role in SERS. The local EM field enhancement is strongly related to the collective oscillations of the conduction electrons in the nanostructures – or the localized surface plasmon resonances (LSPRs) – that can be excited by external light irradiation. The field enhancement is obtained by the sharp features of the metastructures through the "lightning rod" effect.

Star benefits

Advantageous properties include the possibility of resonance tuning with respect to the available laser sources, light polarization sensitivity and control on the spatial positions of the hot spots. The star shape is a very appealing geometry in this respect because it provides multiple sharp edges that produce electric field hot spots and it allows for the precise tuning of the resonance energy by varying the overall star size.

Star fabrication

The research group at the Italian Institute of Technology (IIT) fabricates gold nanostar arrays using electron beam lithography and metal evaporation. They are used for chemical sensing of different organic and biomolecules via SERS. The detailed experimental and theoretical study of the optical properties of nanostar arrays with different size demonstrates good wavelength tunability to standard laser sources at 630 and 830 nm. There are also very high SERS enhancement factors that allow to clearly resolve the characteristic Raman bands of the analyte molecules.

More information about the research can be found in the journal Nanotechnology 25 235303.

Further reading

Biocompatible plasmonic substrates assembled for single-molecule detection (Jan 2012)
Hexagon-like nanopattern amplifies virus fingerprint (May 2011)
Understanding the physics of SERS (Sept 2010)