Original Paper

Analytical and Bioanalytical Chemistry

, Volume 394, Issue 7, pp 1819-1825

First online:

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

  • Jeffrey M. McMahonAffiliated withDepartment of Chemistry, Northwestern University
  • , Anne-Isabelle HenryAffiliated withDepartment of Chemistry, Northwestern University
  • , Kristin L. WustholzAffiliated withDepartment of Chemistry, Northwestern University
  • , Michael J. NatanAffiliated withOxonica Materials, Inc.
  • , R. Griffith FreemanAffiliated withOxonica Materials, Inc.
  • , Richard P. Van DuyneAffiliated withDepartment of Chemistry, Northwestern University
  • , George C. SchatzAffiliated withDepartment of Chemistry, Northwestern University Email author 

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access


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