pH-controlled two dimensional gold nanoparticle aggregates for systematic study of local surface plasmon coupling

Xinheng Li, Kaoru Tamada, Baba Iakira, Masahiko Hara

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

We report a way of using citrates, ionic capping molecules on gold nanoparticles, as a 'tuner" to adjust the charge density on the particles by solution pH, in correlation with their association constants (pKa). We have synthesized 10% biotin-capped gold nanoparticles with 90% citrates covering on the remaining surfaces. The controlled electrostatic repulsion force between the particles determines the distance between the particles on substrate, i.e., the surface density of the particles, even for the case of immobilization via biotin-avidin reaction. Thus the density of gold nanoparticles on surface was varied in a wide range systematically, especially to high density, and the optical response of two dimensional particle aggregates was investigated to discuss the effect of local plasmon coupling. The UV-vis-Near-IR reflection absorption spectrum of the particle aggregates at low pH (pH <pKa2) appeared with a transverse resonance at ca. A = 520 nm and a longitudinal resonance widened and red-shifted to A = 680 nm. Surface plasmon resonance (SPR) curve of the aggregates exhibits a large shift of the minimum angle position together with a significant increase of the minimum intensity (dip-up), as opposed to a small angle shift and no dip-up for well-dispersed particles. The deviation from the SPR simulation curves based on the Maxwell-Garnett (MG) theory clearly indicates the effect of local plasmon coupling in aggregates. The Kramers-Kronig transformations of the UV-vis-Near-IR spectra and the SPR data analyses with Fresnel's equations state the increase of the effective dielectric constants of the particle layers with the density of the particles and the formation of aggregates.

Original languageEnglish
Pages (from-to)408-416
Number of pages9
JournalJournal of nanoscience and nanotechnology
Volume9
Issue number1
DOIs
Publication statusPublished - Jan 1 2009

Fingerprint

Surface Plasmon Resonance
Citrates
Gold
Nanoparticles
gold
Biotin
Surface plasmon resonance
nanoparticles
Avidin
Static Electricity
surface plasmon resonance
Immobilization
biotin
citrates
Charge density
Absorption spectra
Electrostatics
Permittivity
shift
Molecules

All Science Journal Classification (ASJC) codes

  • Bioengineering
  • Chemistry(all)
  • Biomedical Engineering
  • Materials Science(all)
  • Condensed Matter Physics

Cite this

pH-controlled two dimensional gold nanoparticle aggregates for systematic study of local surface plasmon coupling. / Li, Xinheng; Tamada, Kaoru; Iakira, Baba; Hara, Masahiko.

In: Journal of nanoscience and nanotechnology, Vol. 9, No. 1, 01.01.2009, p. 408-416.

Research output: Contribution to journalArticle

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