Two-dimensional bipyramid plasmonic nanoparticle liquid crystalline superstructure with four distinct orientational packing orders

Qianqian Shi, Kae Jye Si, Debabrata Sikdar, Lim Wei Yap, Malin Premaratne, Wenlong Cheng

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Anisotropic plasmonic nanoparticles have been successfully used as constituent elements for growing ordered nanoparticle arrays. However, orientational control over their spatial ordering remains challenging. Here, we report on a self-assembled two-dimensional (2D) nanoparticle liquid crystalline superstructure (NLCS) from bipyramid gold nanoparticles (BNPs), which showed four distinct orientational packing orders, corresponding to horizontal alignment (H-NLCS), circular arrangement (C-NLCS), slanted alignment (S-NLCS), and vertical alignment (V-NLCS) of constituent particle building elements. These packing orders are characteristic of the unique shape of BNPs because all four packing modes were observed for particles with various sizes. Nevertheless, only H-NLCS and V-NLCS packing orders were observed for the free-standing ordered array nanosheets formed from a drying-mediated self-assembly at the air/water interface of a sessile droplet. This is due to strong surface tension and the absence of particle-substrate interaction. In addition, we found the collective plasmonic coupling properties mainly depend on the packing type, and characteristic coupling peak locations depend on particle sizes. Interestingly, surface-enhanced Raman scattering (SERS) enhancements were heavily dependent on the orientational packing ordering. In particular, V-NLCS showed the highest Raman enhancement factor, which was about 77-fold greater than the H-NLCS and about 19-fold greater than C-NLCS. The results presented here reveal the nature and significance of orientational ordering in controlling plasmonic coupling and SERS enhancements of ordered plasmonic nanoparticle arrays.

Original languageEnglish
Pages (from-to)967-976
Number of pages10
JournalACS Nano
Issue number1
Publication statusPublished - 26 Jan 2016


  • Bipyramid nanoparticles
  • Orientational packing
  • Plasmonic nanoparticle liquid crystalline superstructure
  • Self-assembly
  • SERS

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