Analytical and Bioanalytical Chemistry

, Volume 394, Issue 7, pp 1819–1825 | Cite as

Gold nanoparticle dimer plasmonics: finite element method calculations of the electromagnetic enhancement to surface-enhanced Raman spectroscopy

  • Jeffrey M. McMahon
  • Anne-Isabelle Henry
  • Kristin L. Wustholz
  • Michael J. Natan
  • R. Griffith Freeman
  • Richard P. Van Duyne
  • George C. Schatz
Original Paper


Finite element method calculations were carried out to determine extinction spectra and the electromagnetic (EM) contributions to surface-enhanced Raman spectroscopy (SERS) for 90-nm Au nanoparticle dimers modeled after experimental nanotags. The calculations revealed that the EM properties depend significantly on the junction region, specifically the distance between the nanoparticles for spacings of less than 1 nm. For extinction spectra, spacings below 1 nm lead to maxima that are strongly red-shifted from the 600-nm plasmon maximum associated with an isolated nanoparticle. This result agrees qualitatively well with experimental transmission electron microscopy images and localized surface plasmon resonance spectra that are also presented. The calculations further revealed that spacings below 0.5 nm, and especially a slight fusing of the nanoparticles to give tiny crevices, leads to EM enhancements of 1010 or greater. Assuming a uniform coating of SERS molecules around both nanoparticles, we determined that regardless of the separation, the highest EM fields always dominate the SERS signal. In addition, we determined that for small separations less than 3% of the molecules always contribute to greater than 90% of the signal.


Finite element method Surface-enhanced Raman spectroscopy Electromagnetic field enhancement Nanoparticle dimer 



This research was supported by the NSF (CHE-0414554), AFOSR/DARPA Project BAA07-61 (FA9550-08-1-0221), and NSF MRSEC (DMR-0520513) at the Materials Research Center of Northwestern University. We thank the NUANCE Center at Northwestern University for providing access to the TEM equipment.

Supplementary material

216_2009_2738_MOESM1_ESM.pdf (196 kb)
ESM 1 Probability distributions of electromagnetic enhancements for nanoparticle separations from 5 to −20 nm; Percentage and number of molecules that contribute to the SERS signal for particle separations of 5 to −20 nm and molecular diameters of 0.25 to 2 nm (PDF 195 kb).


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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Jeffrey M. McMahon
    • 1
  • Anne-Isabelle Henry
    • 1
  • Kristin L. Wustholz
    • 1
  • Michael J. Natan
    • 2
  • R. Griffith Freeman
    • 2
  • Richard P. Van Duyne
    • 1
  • George C. Schatz
    • 1
  1. 1.Department of ChemistryNorthwestern UniversityEvanstonUSA
  2. 2.Oxonica Materials, Inc.Mountain ViewUSA

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