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The effects of Au aggregate morphology on surface-enhanced Raman scattering enhancement.
J Chem Phys. 2006 Sep 28; 125(12):124707.JC

Abstract

We have identified empirically a relationship between the surface morphology of small individual aggregates (<100 Au nanoparticles) and surface-enhanced Raman scattering (SERS) enhancement. We have found that multilayer aggregates generated greater SERS enhancement than aggregates limited to two-dimensional (2D) or one-dimensional structures, independent of the number of particles. SERS intensity was measured using the 730 cm(-1) vibrational mode of the adsorbed adenine molecule on 75 nm Au particles, at an excitation wavelength of 632.8 nm. To gain insight into these relationships and its mechanism, we developed a qualitative model that considers the collections of interacting Au nanoparticles of an individual aggregate as a continuous single entity that retains its salient features. We found the dimensions of the modeled surface features to be comparable with those found in rough metal surfaces, known to sustain surface plasmon resonance and generate strong SERS enhancement. Among the aggregates that we have characterized, a three 75 nm nanoparticle system was the smallest to generate strong SERS enhancement. However, we also identified single individual Au nanoparticles as SERS active at the same wavelength, but with a diameter twice in size. For example, we observed a symmetric SERS-active particle of 180 nm in diameter. Such individual nanoparticles generated SERS enhancement on the same order of magnitude as the small monolayer Au aggregates, an intensity value significantly stronger than predicted in recent theoretical studies. We also found that an aspect of our model that relates the dimensions of its features to SERS enhancement is also applicable to single individual Au particles. We conclude that the size of the nanoparticle itself, or the size of a protrusion of an irregularly shaped single Au particle, will contribute to SERS enhancement provided that its dimensions satisfy the conditions for plasmon resonance. In addition, by considering the ratio of the generated intensities of typical 2D Au aggregates to the enhancement of individual SERS-active particles, a value of approximately 2 is determined. Its moderate value suggests that it is not the aggregation effect that is responsible for much of the observed SERS enhancement but the surface region associated with the SERS-active site.

Authors+Show Affiliations

Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA. isaac@otto.harvard.edu

Pub Type(s)

Journal Article

Language

eng

PubMed ID

17014200

Citation

Sztainbuch, Isaac W.. "The Effects of Au Aggregate Morphology On Surface-enhanced Raman Scattering Enhancement." The Journal of Chemical Physics, vol. 125, no. 12, 2006, p. 124707.
Sztainbuch IW. The effects of Au aggregate morphology on surface-enhanced Raman scattering enhancement. J Chem Phys. 2006;125(12):124707.
Sztainbuch, I. W. (2006). The effects of Au aggregate morphology on surface-enhanced Raman scattering enhancement. The Journal of Chemical Physics, 125(12), 124707.
Sztainbuch IW. The Effects of Au Aggregate Morphology On Surface-enhanced Raman Scattering Enhancement. J Chem Phys. 2006 Sep 28;125(12):124707. PubMed PMID: 17014200.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - The effects of Au aggregate morphology on surface-enhanced Raman scattering enhancement. A1 - Sztainbuch,Isaac W, PY - 2006/10/4/pubmed PY - 2006/10/4/medline PY - 2006/10/4/entrez SP - 124707 EP - 124707 JF - The Journal of chemical physics JO - J Chem Phys VL - 125 IS - 12 N2 - We have identified empirically a relationship between the surface morphology of small individual aggregates (<100 Au nanoparticles) and surface-enhanced Raman scattering (SERS) enhancement. We have found that multilayer aggregates generated greater SERS enhancement than aggregates limited to two-dimensional (2D) or one-dimensional structures, independent of the number of particles. SERS intensity was measured using the 730 cm(-1) vibrational mode of the adsorbed adenine molecule on 75 nm Au particles, at an excitation wavelength of 632.8 nm. To gain insight into these relationships and its mechanism, we developed a qualitative model that considers the collections of interacting Au nanoparticles of an individual aggregate as a continuous single entity that retains its salient features. We found the dimensions of the modeled surface features to be comparable with those found in rough metal surfaces, known to sustain surface plasmon resonance and generate strong SERS enhancement. Among the aggregates that we have characterized, a three 75 nm nanoparticle system was the smallest to generate strong SERS enhancement. However, we also identified single individual Au nanoparticles as SERS active at the same wavelength, but with a diameter twice in size. For example, we observed a symmetric SERS-active particle of 180 nm in diameter. Such individual nanoparticles generated SERS enhancement on the same order of magnitude as the small monolayer Au aggregates, an intensity value significantly stronger than predicted in recent theoretical studies. We also found that an aspect of our model that relates the dimensions of its features to SERS enhancement is also applicable to single individual Au particles. We conclude that the size of the nanoparticle itself, or the size of a protrusion of an irregularly shaped single Au particle, will contribute to SERS enhancement provided that its dimensions satisfy the conditions for plasmon resonance. In addition, by considering the ratio of the generated intensities of typical 2D Au aggregates to the enhancement of individual SERS-active particles, a value of approximately 2 is determined. Its moderate value suggests that it is not the aggregation effect that is responsible for much of the observed SERS enhancement but the surface region associated with the SERS-active site. SN - 0021-9606 UR - https://www.unboundmedicine.com/medline/citation/17014200/The_effects_of_Au_aggregate_morphology_on_surface_enhanced_Raman_scattering_enhancement_ L2 - https://doi.org/10.1063/1.2338029 DB - PRIME DP - Unbound Medicine ER -
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