Drastic Surface Plasmon Mode Shifts in Gold Nanorods Due to Electron Charging


The color of small gold rods changes dramatically when electrons are injected by chemical reductants. The longitudinal and transverse plasmon modes are both found to blue-shift, and the shift is larger for rods with larger aspect ratios. The color changes are visible to the eye for rods with aspect ratios around 2–3. It is found that the surface plasmon band is damped when charging becomes high. The effects are in qualitative agreement with a model in which the gold plasma frequency increases due to an increase in electron density.

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  1. 1.

    Mulvaney P (1996) Surface plasmon spectroscopy of nanosized metal particles. Langmuir 12:788

    Article  CAS  Google Scholar 

  2. 2.

    Henglein A, Mulvaney P, Linnert T (1991) Chemistry of Agn Aggregates in Aqueous-Solution—Nonmetallic Oligomeric Clusters and Metallic Particles. Faraday Discuss 92:31

    Article  CAS  Google Scholar 

  3. 3.

    Henglein A, Meisel D (1998) Radiolytic Control of the Size of Colloidal Gold Nanoparticles. Langmuir 14:7392

    Article  CAS  Google Scholar 

  4. 4.

    Ung T, Giersig M, Dunstan D, Mulvaney P (1997) Spectroelectrochemistry of Colloidal Silver. Langmuir 13:1773

    Article  CAS  Google Scholar 

  5. 5.

    Chapman R, Mulvaney P (2001) Electro-optical shifts in silver nanoparticle films. Chem Phys Lett 349:358

    Article  CAS  Google Scholar 

  6. 6.

    Toyota A, Nakashima N, Sagara T (2004) UV-visible transmission-absorption spectral study of Au nanoparticles on a modified ITO electrode at constant potentials and under potential modulation. J Electroanal Chem 565:335

    Article  CAS  Google Scholar 

  7. 7.

    Schmidt GM, Curley-Fiorino ME (1975) In: Bard AJ (ed) Encyclopaedia of Electrochemistry of the Elements. Dekker, New York

    Google Scholar 

  8. 8.

    Nikoobakht B, El-Sayed MA (2003) Preparation and growth mechanism of gold nanorods (NRs) using seed-mediated growth method. Chem Mater 15:1957

    Article  CAS  Google Scholar 

  9. 9.

    Pérez-Juste J, Liz-Marzán LM, Carnie S, Chan DYC, Mulvaney P (2004) Electric Field Directed Growth of Gold Nanorods in Aqueous Surfactant Solutions. Adv Funct Mater 14:571

    Article  Google Scholar 

  10. 10.

    Wang ZL, Mohamed MB, Link S, El-Sayed MA (1999) Surface reconstruction of the unstable {110} surface in gold nanorods. Surf Sci 440:L809

    Article  CAS  Google Scholar 

  11. 11.

    Sönnichsen C, Franzl T, Wilk T, von Plessen G, Feldmann J, Wilson O, Mulvaney P (2002) Drastic reduction of plasmon damping in gold nanorods. Phys Rev Lett 88:77402

    Article  Google Scholar 

  12. 12.

    Palik E (1985) Handbook of Optical Constants of Solids Academic Press, Orlando, FL

    Google Scholar 

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P.M. wishes to thank the Humboldt Foundation for financial support and Stiftung Caesar. This work was supported through ARC Grant DP 0451651. LMLM acknowledges financial support from the Spanish Ministerio de Educación y Ciencia and FEDER (project # MAT2004-02991).

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Correspondence to Paul Mulvaney.



Calculation of the Spectra in Figure 6

To calculate the spectrum of polydisperse, charged gold nanorods within the dipole approximation, we first decompose the complex dielectric function [12] into an interband component, which is independent of size, shape, and charge, and a free electron or Drude component,

$$ \varepsilon {\left( \omega \right)} = \varepsilon _{{\operatorname{int} }} {\left( \omega \right)} + \varepsilon _{{{\text{free}}}} {\left( \omega \right)} $$

We then subtract the free electron contribution and add a modified Drude function in which the plasma frequency is modified by an amount \(\omega ^{{\text{2}}}_{{\text{p}}} = {\left( {1 + \Delta N} \right)}{Ne^{2} } \mathord{\left/ {\vphantom {{Ne^{2} } {m\varepsilon _{0} }}} \right. \kern-\nulldelimiterspace} {m\varepsilon _{0} }\)and recalculate the new dielectric function. This enables us to calculate the entire spectrum of the charged gold rods, not just the region around the plasmon modes.

$$ \varepsilon {\left( {\omega ,\Delta N} \right)} = \varepsilon _{{\operatorname{int} }} {\left( \omega \right)} - \varepsilon _{{{\text{free}}}} {\left( \omega \right)} + \varepsilon _{{{\text{free}}}} {\left( {\omega ,\Delta N} \right)} $$

The Drude term becomes:

$$\varepsilon _{{{\text{free}}}} {\left( {\omega ,\Delta N} \right)} = \frac{{N{\left( {1 + \Delta N} \right)}{e^{2} } \mathord{\left/ {\vphantom {{e^{2} } {m\varepsilon _{0} }}} \right. \kern-\nulldelimiterspace} {m\varepsilon _{0} }}}{{\omega ^{2} + i\omega \gamma }}$$

The uncharged metal has ΔN = 0. In an aqueous environment, the metal particles may be cathodically or anodically charged causing electron density changes of up to 10–15%. This modified dielectric function is used in the standard equations for absorption of light by ellipsoids within the dipole approximation and numerically integrated over the size distribution.

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Mulvaney, P., Pérez-Juste, J., Giersig, M. et al. Drastic Surface Plasmon Mode Shifts in Gold Nanorods Due to Electron Charging. Plasmonics 1, 61–66 (2006). https://doi.org/10.1007/s11468-005-9005-0

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  • Gold rods
  • Surface plasmon band
  • Electron density
  • Plasmon band shift
  • Color changes