Heightened electromagnetic fields between metal nanoparticles: Surface enhanced raman scattering from metal - Cytochrome c-metal sandwiches

Christine Dolan Keating, Kenneth K. Kovaleski, Michael J. Natan

Research output: Contribution to journalArticle

103 Citations (Scopus)

Abstract

This manuscript reports the demonstration of strong interparticle electromagnetic coupling in nanoparticle: molecule:nanoparticle sandwiches. These assemblies were prepared by adsorption of cytochrome c (Cc)-coated colloidal Au nanoparticles onto aggregated colloidal Ag. Surface enhanced Raman scattering (SERS) spectra for the Cc:Au conjugates (Ag:Cc:Au) were compared to those obtained by direct adsorption of Cc (Ag:Cc) at several visible excitation wavelengths. The use of identically prepared samples with the same effective [Cc] and the same laser power allows the effects of sample geometry and interparticle coupling to be probed. As expected, at all excitation wavelengths, Ag:Cc:Au gave less intense spectra than Ag:Cc, because (i) only a small percentage of the Cc molecules were close to the more SERS-active metal (Ag), and (ii) the heme, from which all observed vibrations arise, was oriented toward the Au, not the Ag. Nonetheless, the ratio of Ag:Cc:Au to Ag:Cc SERS intensity varied significantly with excitation wavelength, a phenomenon that can be accounted for only by a wavelength-dependent electromagnetic field. This, in turn, results from wavelength-dependent electromagnetic coupling between closely spaced colloidal Ag and colloidal Au. In addition to wavelength-dependent SERS intensity ratios, three separate lines of evidence support the existence of strong electromagnetic coupling: (i) the presence of a wavelength-shifted single particle surface plasmon band for Cc:Au conjugates upon exposure to agggregated Ag, (ii) demonstration of excitation wavelength-dependent photodriven conformational changes in Ag:Cc:Au, and (iii) dramatic increases in SERS intensities from protein - colloid conjugates prepared with Ag in place of Au.

Original languageEnglish (US)
Pages (from-to)9414-9425
Number of pages12
JournalJournal of Physical Chemistry B
Volume102
Issue number47
StatePublished - Nov 19 1998

Fingerprint

Metal nanoparticles
cytochromes
Cytochromes c
Electromagnetic fields
Raman scattering
electromagnetic fields
Metals
Raman spectra
Proteins
nanoparticles
metals
Wavelength
Electromagnetic coupling
wavelengths
electromagnetic coupling
Nanoparticles
excitation
Demonstrations
Adsorption
Molecules

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

Cite this

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title = "Heightened electromagnetic fields between metal nanoparticles: Surface enhanced raman scattering from metal - Cytochrome c-metal sandwiches",
abstract = "This manuscript reports the demonstration of strong interparticle electromagnetic coupling in nanoparticle: molecule:nanoparticle sandwiches. These assemblies were prepared by adsorption of cytochrome c (Cc)-coated colloidal Au nanoparticles onto aggregated colloidal Ag. Surface enhanced Raman scattering (SERS) spectra for the Cc:Au conjugates (Ag:Cc:Au) were compared to those obtained by direct adsorption of Cc (Ag:Cc) at several visible excitation wavelengths. The use of identically prepared samples with the same effective [Cc] and the same laser power allows the effects of sample geometry and interparticle coupling to be probed. As expected, at all excitation wavelengths, Ag:Cc:Au gave less intense spectra than Ag:Cc, because (i) only a small percentage of the Cc molecules were close to the more SERS-active metal (Ag), and (ii) the heme, from which all observed vibrations arise, was oriented toward the Au, not the Ag. Nonetheless, the ratio of Ag:Cc:Au to Ag:Cc SERS intensity varied significantly with excitation wavelength, a phenomenon that can be accounted for only by a wavelength-dependent electromagnetic field. This, in turn, results from wavelength-dependent electromagnetic coupling between closely spaced colloidal Ag and colloidal Au. In addition to wavelength-dependent SERS intensity ratios, three separate lines of evidence support the existence of strong electromagnetic coupling: (i) the presence of a wavelength-shifted single particle surface plasmon band for Cc:Au conjugates upon exposure to agggregated Ag, (ii) demonstration of excitation wavelength-dependent photodriven conformational changes in Ag:Cc:Au, and (iii) dramatic increases in SERS intensities from protein - colloid conjugates prepared with Ag in place of Au.",
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Heightened electromagnetic fields between metal nanoparticles : Surface enhanced raman scattering from metal - Cytochrome c-metal sandwiches. / Keating, Christine Dolan; Kovaleski, Kenneth K.; Natan, Michael J.

In: Journal of Physical Chemistry B, Vol. 102, No. 47, 19.11.1998, p. 9414-9425.

Research output: Contribution to journalArticle

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T2 - Surface enhanced raman scattering from metal - Cytochrome c-metal sandwiches

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AU - Kovaleski, Kenneth K.

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AB - This manuscript reports the demonstration of strong interparticle electromagnetic coupling in nanoparticle: molecule:nanoparticle sandwiches. These assemblies were prepared by adsorption of cytochrome c (Cc)-coated colloidal Au nanoparticles onto aggregated colloidal Ag. Surface enhanced Raman scattering (SERS) spectra for the Cc:Au conjugates (Ag:Cc:Au) were compared to those obtained by direct adsorption of Cc (Ag:Cc) at several visible excitation wavelengths. The use of identically prepared samples with the same effective [Cc] and the same laser power allows the effects of sample geometry and interparticle coupling to be probed. As expected, at all excitation wavelengths, Ag:Cc:Au gave less intense spectra than Ag:Cc, because (i) only a small percentage of the Cc molecules were close to the more SERS-active metal (Ag), and (ii) the heme, from which all observed vibrations arise, was oriented toward the Au, not the Ag. Nonetheless, the ratio of Ag:Cc:Au to Ag:Cc SERS intensity varied significantly with excitation wavelength, a phenomenon that can be accounted for only by a wavelength-dependent electromagnetic field. This, in turn, results from wavelength-dependent electromagnetic coupling between closely spaced colloidal Ag and colloidal Au. In addition to wavelength-dependent SERS intensity ratios, three separate lines of evidence support the existence of strong electromagnetic coupling: (i) the presence of a wavelength-shifted single particle surface plasmon band for Cc:Au conjugates upon exposure to agggregated Ag, (ii) demonstration of excitation wavelength-dependent photodriven conformational changes in Ag:Cc:Au, and (iii) dramatic increases in SERS intensities from protein - colloid conjugates prepared with Ag in place of Au.

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