Design and simple assembly of gold nanostar bioconjugates for surface-enhanced raman spectroscopy immunoassays

Maria João Oliveira, Miguel P. de Almeida, Daniela Nunes, Elvira Fortunato, Rodrigo Martins, Eulália Pereira, Hugh J. Byrne, Hugo Águas, Ricardo Franco

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


Immunoassays using Surface-Enhanced Raman Spectroscopy are especially interesting on account not only of their increased sensitivity, but also due to its easy translation to point-of-care formats. The bases for these assays are bioconjugates of polyclonal antibodies and anisotropic gold nanoparticles functionalized with a Raman reporter. These bioconjugates, once loaded with the antigen analyte, can react on a sandwich format with the same antibodies immobilized on a surface. This surface can then be used for detection, on a microfluidics or immunochromatographic platform. Here, we have assembled bioconjugates of gold nanostars functionalized with 4-mercaptobenzoic acid, and anti-horseradish peroxidase antibodies. The assembly was by simple incubation, and agarose gel electrophoresis determined a high gold nanostar to antibody binding constant. The functionality of the bioconjugates is easy to determine since the respective antigen presents peroxidase enzymatic activity. Furthermore, the chosen antibody is a generic immunoglobulin G (IgG) antibody, opening the application of these principles to other antibody-antigen systems. Surface-Enhanced Raman Spectroscopy analysis of these bioconjugates indicated antigen detection down to 50 _U of peroxidase activity. All steps of conjugation were fully characterized by ultraviolet-visible spectroscopy, dynamic light scattering, ζ-Potential, scanning electron microscopy, and agarose gel electrophoresis. Based on the latter technique, a proof-of-concept was established for the proposed immunoassay.

Original languageEnglish
Article number1561
Issue number11
Publication statusPublished - 1 Nov 2019


  • Agarose gel electrophoresis
  • Dynamic light scattering
  • Enhanced Raman Spectroscopy
  • Gold nanoparticles
  • Gold nanostars
  • Horseradish peroxidase
  • Immunoassay
  • Immunoconjugates
  • Raman reporter
  • Surface enhanced Raman spectroscopy Surface


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