Plasmonics

, Volume 8, Issue 1, pp 53–62 | Cite as

Comparative Study of Plasmonic Properties of Cysteine-Functionalized Gold and Silver Nanoparticle Aggregates

  • Anikó Szalai
  • Áron Sipos
  • Edit Csapó
  • László Tóth
  • Mária Csete
  • Imre Dékány
Article

Abstract

The absorptance spectra of gold and silver nanoparticle (NP) aqueous dispersions were measured by UV–visible spectroscopy and computed numerically by finite element method. Both NPs were functionalized by l-cysteine amino acid (Cys) in order to develop aggregate-based localized surface plasmon resonance biosensors. Absorptance spectra measured at an analogous pH value of ∼4.9 were compared, where Au-Cys conjugates have moderately split spectra with two commensurate maxima, while Ag-Cys conjugates exhibit the most pronounced secondary peak according to the highest degree of aggregation. The purpose of our theoretical study was to determine the simplest linear chain-like and wavy aggregate geometries, which result in maxima matching the measured peaks. The aggregates were characterized by N number and d diameter of NPs, g gap between the NPs, and t thickness of the l-cysteine covering. By tuning the angle of incidence and E-field oscillation direction in p-polarized light with respect to the aggregates, the contribution of longitudinal and transversal modes was varied. The comparison of measurements and computations revealed that spectra measured on bioconjugate dispersions include effects of numerous aggregates with various geometries, illuminated from different directions and are influenced by inter-aggregate coupling. Inspecting the normalized E-field distribution surrounding the aggregates, it was shown that fundamentally different multipolar modes can be identified at primary and secondary absorptance maxima, due to coupled plasmonic resonances on NPs.

Keywords

Nanoparticle aggregates LSPR spectra Coupled plasmonic resonances Array effect 

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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  • Anikó Szalai
    • 1
  • Áron Sipos
    • 1
  • Edit Csapó
    • 2
  • László Tóth
    • 3
  • Mária Csete
    • 1
  • Imre Dékány
    • 2
    • 3
  1. 1.Department of Optics and Quantum ElectronicsUniversity of SzegedSzegedHungary
  2. 2.Supramolecular and Nanostructured Materials Research Group of the Hungarian Academy of SciencesUniversity of SzegedSzegedHungary
  3. 3.Department of Medical Chemistry, Faculty of MedicineUniversity of SzegedSzegedHungary

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