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A*STAR Singapore - Photonics as deconstructed nano-sensors light the way forward

DCN Corp - Electron microscope images of two different plasmonic structures that researchers can deconstruct into sub-units to determine optical properties.  Credit - © 2012 American Chemical SocietyA highly flexible approach has been designed for photonic nano-sensors and is now available, which could potentially overcome practicality and reliability issues.  As has been previously stated metallic nano-structures can act as tiny antennae to control light since they can focus and guide light on the smallest scales.  The fabricated size and shape of such antennae dictates the overall quality of the optical properties - making it very difficult to predict which shape to select for a desired optical effect without being over reliant on complex theoretical calculations.  Therefore, it is claimed by an international team of researchers in between A*STAR Data Storage Institute, Signapore, and Imperial College London (ICL), UK - led by Mohsen Rahmani, that they have developed a method, which enables for both the practical and reliable design of such nano-antennae.

The method is based on a new understanding of the optical resonance properties of a few 'standardised' building-blocks which give rise to surface plasmons.  Plasmons is the collective movement of electrons at a surface interface.  As stated by Rahmani - "our novel understanding captures aspects of device design that extend well beyond known optical interference mechanisms and significantly advances our understanding of the plasmonic resonance spectrum.  This could bring about new applications,"

Commercially the most useful properties of plasmonic antennae occur when the metal nano-structures are brought within close proximity to each other.  However, the proximity has to be of a homogeneous nature and not 'cluster-like' islands.  The closeness can lead to interference effects near their surface, which can cause sharp spectral features - dubbed Fano resonances.  Any alterations near the nano-structures, such as the introduction of a few molecules or fluctuations in temperature, can impact the sensitivity of the Fano resonances.  Such slight changes can be detected and employed for bio-sensing applications.

To understand the iterative nature - researchers typically employ computer models for the nano-structures, which enable for the optimisation of the plasmonic antennae design.  Interestingly Rahmani and co-workers simplified their approach by employing standardised sub-units of nanoparticles - called plasmonic oligomers.  Rahmani's team deconstructed a cross-shaped structure, which consists of 5 dots into 2 sub-units.  Subsequently they determined the plasmonic resonance of an entire array by simply combining the sub-units.

In seeking to stimulate the properties of the oligomers and comparing such results with measurements of an optical spectra, then Rahmani observed a systematic dependence of their optical resonances based on individual sub-units.  The team's observations suggested that the optical properties of various plasmonic antennae can be designed easily from just a few basic building blocks.  Rahmani concludes by stating "the possible combinations are almost endless and these structures could find many applications," from nano-scale lasers and optical switches for tele-communications to bio-sensing.  In conclusion, Rahmani stated their future plans are "we are now going to develop these oligomers as nano-sensing platforms for detecting the adsorption of chemical molecules and protein mono-layers."  Original article available here.

DCN Corp finds Rahmani's research and that of other A*STAR nanotechnology breakthroughs very promising - especially when considering that DCN Corp can also homogeneously fabricate nano-particulates leading to a novel reproducible/repeatable bio-sensor platform technology.  Moving forward - if you or your colleagues are interested in making the above a reality - please ensure to contact the company as soon as practicably possible.