Effect of Medium for Enhanced Nanosensing – DDA Theory vs Experimental Studies of Ag Nanoparticle Assemblies


  1. Wang, S.
  2. Pedersen, D.B.
Corporate Authors
Defence R&D Canada - Suffield, Ralston ALTA (CAN)
Gas-phase deposition has been used to assemble two-dimensional ensembles of strongly coupled 3.0 ± 0.5 nm diameter naked Ag nanoparticles. The coupling mechanism is found to be complex suggesting dipole-dipole coupling at relatively long distances but wave function overlap at center-to-center distances less than 25 nm. The coupled nanoparticles are found to display enhanced sensitivity to changes in the refractive index of the medium, relative to the isolated particle system, and the experiments confirm theoretical predictions of the enhancement effect. For the Ag nanoparticles considered, the enhancement effect is interesting as the coupling energy between particles is found to be remarkably insensitive to the medium and changing the surrounding material from air to hexane has no noticeable effect on this energy. At the same time, changing the medium from air to hexane always manifests a 0.14 eV shift (as for the individual nanoparticle) independent of interparticle coupling and distance. In noncoupled systems the SPR appears at shorter wavelength where the 0.14 eV energy amounts to a relatively small shift in the peak position wavelength. In coupled systems, however, the SPR is positioned at relatively long wavelengths and 0.14 eV is a large shift in wavelength units. As the enhancement is the wavelength change per refractive index unit, more coupled systems yield higher enhancement. The fact that enhanced sensitivity is observed in two-dimensional assemblies of nanopartic
Report Number
DRDC-SUFFIELD-SL-2009-172 — Scientific Literature
Date of publication
01 Nov 2009
Number of Pages
Reprinted from
J. Phys. Chem. C, vol 114, 2010, p 2861-2866
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