Hotspot-induced transformation of surface-enhanced Raman scattering fingerprints

Tao Chen, Hong Wang, Gang Chen, Yong Wang, Yuhua Feng, Wei Shan Teo, Tao Wu, Hongyu Chen*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

165 Scopus citations

Abstract

The most studied effect of surface-enhanced Raman scattering (SERS) hotspots is the enormous Raman enhancement of the analytes therein. A less known effect, though, is that the formation of hotspots may cause the trapped analytes to change molecular orientation, which in turn leads to pronounced changes in SERS fingerprints. Here, we demonstrate this effect by creating and characterizing hotspots in colloidal solutions. Anisotropically functionalized Au nanorods were synthesized, whereby the sides were specifically encapsulated by polystyrene-block-poly(acrylic acid), leaving the ends unencapsulated and functionalized by a SERS analyte, 4-mercaptobenzoic acid. Upon salt treatment, these nanorods assemble into linear chains, forming hotspots that incorporate the SERS analyte. Enormous SERS enhancement was observed, particularly for some weak/inactive SERS modes that were not present in the original spectrum before the hotspots formation. Detailed spectral analysis showed that the variations of the SERS fingerprint were consistent with the reorientation of analyte molecules from nearly upright to parallel/tilted conformation on the Au surface. We propose that the aggregation of Au nanorods exerts physical stress on the analytes in the hotspots, causing the molecular reorientation. Such a hotspot-induced variation of SERS fingerprints was also observed in several other systems using different analytes.

Original languageEnglish (US)
Pages (from-to)3087-3094
Number of pages8
JournalACS Nano
Volume4
Issue number6
DOIs
StatePublished - Jun 22 2010

Keywords

  • Au nanorod
  • Fingerprint
  • Hotspot
  • Linear aggregation
  • SERS

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

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